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The present study investigated the aerosol-radiation-cloud interaction of anthropogenic black carbon (BC) during a severe fog-haze event by utilizing WRF-Chem, multi-satellite and in-situ observations, reanalyses datasets, and HYSPLIT model. The WRF-Chem model adequately captured the regional distribution of aerosol, cloud, and meteorological variables over the study domain. The maximum BC surface concentration (≥7 μg m−3) was predominantly evident over densely populated central and lower Indo-Gangetic Plain (IGP) regions. Although smoke aerosols usually persisted within 4 km above the surface at daylight hours, they reached as high as 6 km during nighttime, specifically over the central IGP regions. The heavily influenced areas by BC aerosols expanded to almost the entire landmass and the continental outflow region upon doubling the anthropogenic emission. The geographical distribution of maximum perturbations in net shortwave radiation flux at the surface closely matched the spatial patterns of the highest BC concentration, indicating a crucial role of BC in directly preventing the incoming sunlight from reaching the surface. Consequently, the reduced solar radiation at the ground might result in substantial surface cooling (between −0.3 and −0.5 °C), eventually prohibiting surface evapotranspiration and diminishing the outgoing sensible and latent heat fluxes. Also, more amplified cooling in the polluted atmosphere can prevent further development of the planetary boundary layer (PBL), increasing particle entrapment near the surface via an 'aerosol-radiation-PBL' feedback loop. However, the most striking contrast between the two scenarios (typical and polluted) was the prolonged and intensified warming (0.5–0.8 °C) in the mid-troposphere, causing a remarkable drop in moisture (more than two to three times) and hence burn-off of liquid cloud droplets due to the semi-direct effect of increased BC aerosols. The intense mid-tropospheric heating could remarkably enhance the updraft velocity, supporting the vertical transport of the additional moisture to higher altitudes, forming more ice clouds at night. Therefore, the current study highlighted the urgency of mitigating anthropogenic BC emissions in highly polluted regions since increased emissions could considerably worsen severe fog-haze conditions and influence both liquid water and ice clouds, depending on the atmospheric conditions. • Maximum black carbon concentration is observed over the central and lower Indo-Gangetic Plain in the usual scenario. • Perturbation in surface fluxes due to near-surface cooling is more prominent in the polluted scenario. • Black carbon-induced prolonged and intense mid-tropospheric heating is more prominent than the near-surface cooling. • Stronger mid-tropospheric heating accelerates vertical moisture transport and promotes the formation of more ice clouds. [ABSTRACT FROM AUTHOR]

The SPRUCE-22 field campaign was conducted during July 2022 on a remote mountainous forested site in Greece to assess interactions of biogenic and anthropogenic pollutants in the Eastern Mediterranean. Particle chemical composition and size distributions along with concentrations of organic and inorganic gases were measured at high temporal resolution, while samples were collected and analyzed off-line. PM 1 had a surprisingly high average concentration of 13 μg m−3 consisting primarily of organics (57%), followed by sulfate (30%), ammonium (9%), and black carbon (2%). Nitrates (both inorganic and organic) were less than 1% of the PM 1 despite the relatively high NO x emissions in the Balkans. The PM 2.5 concentrations at this remote site were similar and even higher than those in major cities across Greece including Athens, indicating the importance of regional transport for summertime pollution in the Eastern Mediterranean. The relatively constant average diurnal profiles of major anthropogenic pollutants are consistent with only minimal effects from local sources. Sulfates are not any more the dominant component of fine PM in Greece due to the reduction of SO 2 emissions of coal-burning powerplants. The organic aerosol (OA) was quite oxidized with an average oxygen to carbon ratio (O:C) equal to 0.83. The average concentration of isoprene was 0.6 ppb, of monoterpenes 0.5 ppb, while the biogenic secondary organic aerosol factor (obtained through source apportionment analysis) was estimated to contribute 22% of the OA. Additional biogenic secondary organic aerosol (SOA) may be part of the two oxygenated OA (OOA) factors that were also identified. Radiocarbon analysis indicated that the non-fossil carbon was approximately equal to the sum of the biogenic and the more oxidized oxygenated OA, implying that the less oxidized OOA in this study was mostly associated to anthropogenic fossil fuel combustion. The biogenic SOA was quite aged (O:C equal to 0.63) and was also mostly transported to the site. Nearby new particle formation events occurred during 20 % of the days, with an average SO 2 concentration of 0.3 ppb. The oxidative potential of the PM per unit of mass was quite high. The source attribution of the fine PM and the interactions among its anthropogenic and biogenic components are also discussed. [Display omitted] • Organics and not sulfate were the dominant fine PM component. • PM 2.5 concentrations at this remote site were similar to those in Athens. • Highly oxygenated organic aerosol. • Non-fossil carbon equal to sum of biogenic plus more oxidized oxygenated OA. • Nearby new particle formation events occurred during 20% of the days. [ABSTRACT FROM AUTHOR]

The size distribution and hygroscopicity of the refractory black carbon (rBC) aerosol are critical properties for understanding its impact on human health, the extent to which the particles disperse through the atmosphere, and the effect that the particles have on clouds and the climate system. The hygroscopicity of black carbon is primarily controlled by the degree to which the black carbon cores are coated with other compounds. Here we show new measurements of rBC obtained from a single particle soot photometer at an urban location in Houston, TX, USA during the Department of Energy TRacking Aerosol Convection Interactions ExpeRiment (TRACER) campaign. We classified rBC particles into uncoated, thinly coated and thickly coated, where the latter is defined as the optical coating thickness exceeding 10 nm. To understand how aerosol aging and the prevailing winds interact to affect rBC coatings, a slice of the size distribution with rBC core diameter 143–166 nm is considered. For this slice, the average coating thickness of thickly coated particles was 29 ± 8 nm. The rBC number concentration, the fraction of thinly and thickly coated particles, and the average coating thickness strongly vary with the wind direction. We found that onshore flows are associated with lower number concentrations, more thinly coated particles, and thinner coatings when compared to offshore flows. Diurnal profiles show that the fraction of coated particles increases during daytime, likely due to photochemical aging. The estimated fraction of rBC particles that may activate into cloud droplets at 0.1% and 1% water supersaturation was generally ∼0.6% and ∼9%, respectively. This suggests that substantial further aging is needed to precondition the majority of rBC particles for incorporation into cloud droplets. • Onshore flows are associated with lower concentration and thinner coatings. • Photochemical aging increases the fraction of coated particles during daytime. • Fraction of black carbon particles that may activate into cloud droplets is <9%. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols are important absorbing components that can impact the regional climate and environment. To better understand the effects of BC, long-term variations in BC concentrations and the relationships between BC and other air pollutants were investigated in urban Nanjing in the Yangtze River Delta (YRD) based on near-nine-year observations using a seven-channel aethalometer (AE-31). The BC concentrations in YRD city had substantial seasonal and diurnal variations, which are higher in winter (rush hours) and lower in summer (at noon). They had a significant declining trend since 2013 when the Action Plan for Air Pollution Prevention and Control was carried out, which was reduced by at least 45% from 2013 to 2019, and the same applies to heavy pollution episodes. The aerosol absorption coefficient (AAC) had temporal variations similar to those of the BC concentration because BC was the dominant component of absorbing aerosols (>80% at 550 nm). Investigations also indicated that the average contributions of BC from biomass burning (BC bb) and fossil fuel (BC ff) to the total BCs concentration could be of equal importance. However, the ratios of BC bb to the total BCs in colder seasons were much higher than those in summer. Nevertheless, both BC bb and BC ff might significantly contribute to the high BC loadings during particulate pollution episodes. Further comparisons showed that BCs had substantial positive correlations with CO and PM 2.5. The relationships between BC and CO imply that the sources of fossil fuel BC aerosols in Nanjing might mainly came from the combustion of industrial coal and gasoline vehicles. An extremely high BC loading or higher BC/PM 2.5 ratio always corresponded to a lower O 3 concentration, implying that BC might have a substantial influence on O 3 formation. • The interannual variation trend of black carbon is revealed in an urban area of China. • BC from biomass and fossil fuel combustion in the Yangtze River Delta region are qualified. • BC might have a potential influence on tropospheric ozone formation. [ABSTRACT FROM AUTHOR]

Discriminating the absorption coefficients of aerosol mineral dust and black carbon (BC) in different aerosol size fractions is a challenge because of BC's large mass absorption cross-section compared to dust. Ambient aerosol wavelength dependent absorption coefficients (b a b s) in supermicron and submicron size fractions were determined with a high time resolution. The measurements were performed simultaneously using identical systems at an urban and a regional background site in Qatar. At each site, measurements were taken by co-located Aethalometers, one with a virtual impactor (VI) and the other with a PM1 cyclone to respectively collect super-micron-enhanced and submicron fractions. The combined measurement of aerosol absorption and scattering coefficients enabled the particles to be classified based on their optical properties' wavelength dependence. The classification reveals the presence of BC internally/externally mixed with different aerosols. Helium ion microscopy images provided information concerning the extent of mineral dust in the submicron fraction. The determination of absorption coefficients during dust storms and non-dust periods was used to establish the absorption Ångström exponent for dust and BC. Non-parametric wind regression, potential source contribution function and back-trajectory analysis reveal major regional sources of desert dust associated with north-westerly winds and a minor local dust contribution. In contrast, major BC sources found locally were associated with south-westerly winds with a smaller contribution made by offshore emissions transported by north-easterly and easterly winds. The use of a pair of Aethalometers with VI and PM1 inlets separates contributions of BC and dust to the aerosol absorption coefficient. The text discusses a study focused on discriminating between aerosol mineral dust and BC absorption coefficients in various aerosol size fractions. The key highlights from the text are as follows: • Collocated sites measurements: Measurements were conducted simultaneously at both an urban and a regional background site in Qatar using identical systems. Collocated Aethalometers were used, one with a virtual impactor and the other with a PM1 cyclone, to collect supermicron-enhanced and submicron aerosol fractions, respectively. • Classification based on Optical Properties: The combination of aerosol absorption and scattering coefficient measurements allowed for the classification of particles based on the wavelength dependence of their optical properties, revealing the presence of BC internal/external mixing with various aerosols. • Mineral Dust Contribution: HIM images provided information about the contribution of mineral dust in the submicron aerosol fraction. Absorption coefficients were determined during both dust storms and non-dust periods to calculate AAE for dust and BC. • Source apportionment: Back-trajectories, wind regression, and PSCF were used to identify major regional sources of desert dust associated with northwesterly winds and major local BC sources associated with southerly west winds, with some offshore emissions transported by northeasterly and easterly winds. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols directly influence the earth's climate system by absorbing the light intensity and indirectly by interacting with clouds. The microphysical properties of BC-containing aerosols were determined by their core diameter and shell thickness, which can be derived from the measurement of a single-particle soot photometer (SP2). Traditionally, a constant real part of the shell's refractive index (RRI) was employed to retrieve the shell thickness of BC-containing aerosols using the measured scattering signals from SP2. Recent field measurements in East China show that ambient aerosol RRI varies over a wide range between 1.36 and 1.56. The influences of aerosol RRI variation on the retrieving of BC-containing aerosol shell thickness from the measurements of SP2 are investigated with simulation studies. Results show that the variation in ambient aerosol RRI can lead to a variation in the coating thickness of BC-containing aerosols by 9.4%. The corresponding uncertainties in the light absorption enhancement reach up to 29% due to the influence of aerosol RRI. The critical mean supersaturation (SS) of the BC-containing aerosol varies significantly between 0.044% and 0.055% due to the uncertainties in the derived shell thickness using a constant RRI. This study highlights the demand for the real-time measurement of ambient aerosol RRI when deriving the microphysical properties of ambient BC-containing aerosols from the SP2 measurement. • Influence of the variation in aerosol refractive index on the microphysical properties of SP2-measured BC was estimated. • Coating thickness of BC would vary by 9.4% due to the variation in the black carbon coating's refractive index. • The light absorption ability would vary by 29% due to the influence of the aerosol coating's refractive index. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is known to absorb solar radiation and thus have a warming impact on climate. The atmospheric aging of fresh BC has been suggested to enhance BC's light absorption, but the extent of variation observed varies largely in field and laboratory measurements. Biogenic VOCs with much higher abundance than anthropogenic emissions are reactive towards atmospheric oxidants, and act as major sources of secondary organic aerosol (SOA) in the atmosphere. In this study, we performed experiments of BC aging in the presence of condensable organic vapors generated from the ozonolysis of α-pinene. Significant changes in the particle size, mass, effective density, morphology as well as optical properties are observed upon coating of BC by α-pinene ozonolysis products. While the BC aging rate depends on the initial concentrations of precursors forming condensable materials and the particle size, the extent of transformation of BC at a given size is mainly controlled by the volume equivalent coating thickness. The highly fractal BC core is converted to a more compact morphology for a coating thickness of ∼25–30 nm depending on the initial particle size. The absorption and scattering of light by BC also increase by more than 1.29- and 5.30- fold during the coating process. The enhancement of optical properties can be attributed to both formation of coatings and restructuring of the BC core, with the latter accounting for a large fraction of optical enhancement. Our results indicate that the ozonolysis of α-pinene has profound effects on the morphology and optical properties of BC, with a magnitude comparable to sulfuric acid and ammonium nitrate, but much higher than other reported anthropogenic hydrocarbons. Although present in relatively low concentrations, α-pinene oxidation reactions can considerably enhance the impacts of BC on air quality and climate forcing. [Display omitted] • The BC morphology and optical properties can be rapidly and significantly altered by α-pinene ozonolysis products. • The aging induced by α-pinene ozonolysis SOA is significantly greater than oxidation of other anthropogenic hydrocarbons. • The enhancement of absorption and scattering can be attributed to both coatings and restructuring of BC cores during aging. [ABSTRACT FROM AUTHOR]

The mixing state of refractory black carbon (rBC) aerosols is regarded as a major uncertainty in climate-forcing assessments. This study measured the size distribution and mixing state of rBC using a single-particle soot photometer in the winter of 2022 at an urban site in Beijing. During the campaign, the mean mass concentration of rBC was 0.79 ± 0.63 μg m−3, much lower than that observed in Beijing in the winter of 2013. The number and mass median diameter of the rBC cores were 97 and 200 nm, respectively. The average relative coating thicknesses (RCT) of rBC-containing particles was 1.45 ± 0.27 and average light absorption enhancement (Eabs) was 1.43 ± 0.22. Similar to Eabs, RCT and secondary inorganic aerosols (SIA), especially nitrate, increased with increasing relative humidity. This suggests that higher SIA mass fraction in aerosol with a higher relative humidity in the environment results in a thicker coating and black carbon ageing, thus enhancing light absorption. RCT and Eabs increased rapidly with the increase of PM 1 loading but increased slowly when the PM 1 mass concentration exceeded 60 μg m−3. This indicates that a further increase in the NR-PM 1 species at high PM loading does not increase the thickness of the coatings; therefore, there is no further increase in Eabs. The effects of the chemical composition of the Eabs obtained using the Lindeman, Merenda, and Gold method showed that nitrate plays a prominent role in the enhancement of light absorption, followed by SOA. The rBC mass concentration exhibited clear day-low and night-high patterns which were influenced by the synergetic effects of the boundary layer and emissions. RCT and Eabs presented similar diurnal variations, peaking in the afternoon, which was consistent with the pattern of SIA. This suggests that the SIA produced via photochemical reactions supports the ageing of black carbon-containing particles, leading to light-absorption enhancement. The back-trajectory analysis showed the highest values of rBC mass concentration, RCT, and Eabs appeared in the S cluster suggested that the rBC-containing particles transported from south Beijing were more aged with a thicker coating. While the rBC-containing particles from northern and northwestern Beijing had lower RCT and Eabs values. • Nitrate is the dominant contributor to the coatings on BC and prominent role in light-absorption enhancement. • RCT and Eabs increased rapidly as PM 1 loading increased, but slowly when the PM 1 mass concentration exceeded 60 μg m−3. • The rBC- containing particles transported from south Beijing are more aged with a thicker coating. • ∼15% of the NR-PM 1 mass was bound to BC particles. [ABSTRACT FROM AUTHOR]

Black carbon (BC) has been identified as one of the primary contributors to climate change, primarily due to its exceptional capacity to absorb solar radiation. This leads to a reduction in the albedo of ice and snow surfaces, consequently accelerating their melting. In this work, measurements of atmospheric BC are presented, carried out from October 2016 to December 2019 in Portillo, Chilean Central Andes, in the NUNATAK-1 laboratory refuge (3000 m.a.s.l). This site is close to the Chile-Argentina border and is situated along a heavily trafficked road connecting the two countries. Owing to weather conditions, this route operates on a seasonal schedule, remaining open 24 h during warmer months, while in winter, traffic is restricted to the hours between 8 a.m. and 8 p.m. Access to vehicles is prohibited during periods of heavy snowfall. BC concentrations were continuously monitored by a Multi-Angle Absorption Photometer (MAAP). The variability and temporal cycles of BC levels were investigated in relation to local vehicular activity and meteorological parameters, through multiple linear regression analysis. Results show that vehicular traffic variations led to a systematic pattern in the atmospheric BC measured, with a preponderant role of meteorological factors. During the summer months, BC levels reached their peak (mean of 0.77 μg m−3), with maximum values recorded during the nighttime and early morning hours. In line with this finding, summer counted the highest number of vehicles circulating in the area. In contrast, the winter months exhibited lower average BC atmospheric concentrations compared to summer months (0.35 μg m−3), characterized by a distinct hourly profile. In a complementary way, forward trajectories using the HYSPLIT model were performed for various meteorological conditions. The findings indicated that emissions from the study area had the potential to extend to neighboring glaciers. This impact on the basins' hydrology, vital and fragile components of the Andean region, magnifies climate change effects in these cryospheric zones. Notably, the latest IPCC report highlights limited research on aerosol effects on mountain snow and glaciers. This study also presents the first estimates of high-altitude BC source assessments in Chile and South America. These insights could enhance global atmospheric models in mountainous regions, enhancing their accuracy and utility. [Display omitted] • Long-term and high-resolution atmospheric BC was measured in the Chilean Andes. • Vehicular emissions were the primary local source of BC, with modeling suggesting potential impact on nearby glaciers. • Long-range transport was not a significant contribution to BC measured levels. [ABSTRACT FROM AUTHOR]

In this study, the evaluation of carbonaceous fine particulate matter (C-PM) was conducted using the SAFAR-India regional model. Two emission inventories were utilized: the newly developed SAFAR inventory and the global EDGAR-HTAP inventory, both for the year 2018. The simulation aimed to capture the seasonal and spatial patterns of black carbon (BC) and organic carbon (OC) concentrations. To validate model results, surface meteorological parameters, and C-PM concentrations were compared with the MERRA reanalysis data for the Indian region. Model simulated surface C-PM concentration with SAFAR emission inventory is found to be slightly overestimated (1.10), whereas simulated results with EDGAR emission inventory is significantly underestimated as compared to MERRA data. Model-simulated meteorological parameters showed a better correlation with MERRA reanalysis. Simulated geographical patterns of seasonal mean C-PM with SAFAR emission inventory exhibit quite a better comparison with MERRA reanalysis as against EDGAR simulated results. However, some differences in the present results are visible, particularly over the IGP region, as compared to MERRA data, but they are mainly attributed to a significant difference in the special resolution of present results (much finer) as compared to coarser MERRA data. In the Indo-Gangetic Plain (IGP) region, the concentration of BC SF and OC SF (BC and OC with SAFAR emission, respectively) show the peak during the winter, followed by the post-monsoon season. Although the correlation coefficients of hourly time series of surface BC SF and OC SF concentrations with MERRA over India are high (0.92 and 0.88), the poor RMSE, is attributed mainly to different scales of resolution. The model simulated BC, and OC concentrations with SAFAR emission input capture the pattern of spatial distribution reasonably well. The present evolution of BC and OC will help to better quantify their impact on climate and atmospheric conditions over the Indian region. [Display omitted] • C-PM from MERRA compares the simulations with SAFAR & EDGAR emission inventory. • Simulation provides the seasonal variations in BC and OC, with the highest concentrations in the winter at the IGP region. • Meteorology dominates the emissions during the monsoon season in BC and OC variation. • The study suggests that simulated C-PM using SAFAR capture hotspots regions across India as compared to other simulations. [ABSTRACT FROM AUTHOR]

Fires in waste facilities are a common occurrence. Since many waste facilities are located adjacent to densely populated areas, these fires could potentially expose large populations to the emitted pollutants. However, at the moment there are only few field studies investigating the impact of waste fire emissions on air quality since the unpredictable nature of these events makes them challenging to capture. This study investigated the impact of a large and persistent un-prescribed fire in a waste storage facility in Stockholm county, Sweden, on the local air quality of two residential areas in close proximity to the fire. In-situ measurements of particulate matter, black carbon and nitrogen oxide concentrations were conducted both during open burning and after the fire was fully covered. In addition, filter samples were collected for offline analysis of organic composition, metal content and toxicity. Strongly increased concentrations of PM 10 , PM 2.5 and black carbon were found during the open burning period, especially when the wind was coming from the direction of the fire. In addition, elevated concentrations of particulate heavy metals and polycyclic aromatic hydrocarbons were observed in the air during the open burning period. These results show that waste fires can have a strong impact on the air quality of nearby residential areas. • Increased PM 10 , PM 2.5 and black carbon when wind comes from direction of waste fire. • Elevated concentrations of particulate heavy metals and PAHs during open burning. • Waste fires can have a strong impact on air quality of nearby residential areas. [ABSTRACT FROM AUTHOR]

Reducing the uncertainty in aerosol radiative forcing requires a comprehensive understanding of the factors affecting black carbon (BC) light absorption. In this study, the characteristics and influencing factors of light absorption enhancement (E abs) of refractory BC (rBC) were investigated by conducting intensive measurements at an urban site in northwest China during the early summer of 2018. On average, the absorption of rBC was enhanced by 34% as a result of the internal mixing of rBC with other aerosol components. Secondary inorganic aerosols (SIAs) were found to have considerable effects on the E abs of rBC. The E abs showed a robust linear relationship with the bulk nitrate/rBC mass ratio in fine particles, with an increase of 3% per nitrate/rBC ratio unit. A notable increase in E abs from dusk to the next morning was observed, in accordance with the diurnal variations in nitrate and sulfate, indicating the excellent contribution of non-photochemical formation of SIAs to E abs. This fact was further supported by the positive correlation of the nitrate/rBC and sulfate/rBC ratios with relative humidity (RH) rather than photochemical indicators. This study indicates that the aqueous and/or heterogeneous formation of SIAs is likely the dominant aging pathway leading to the high E abs of rBC. • Light absorption enhancement (E abs) of BC by coating was observed in northwest China. • Nitrates and sulfates highly affected the E abs , especially nitrates. • The aqueous and/or heterogeneous formation of nitrates and sulfates played a dominant role in E abs. [ABSTRACT FROM AUTHOR]

The 2021 WHO guidelines recommend limits for black carbon (BC) due to its role in oxidative stress and inflammation. BC is highly light-absorbing and quickly undergoes coating by secondary organic aerosols (SOA), enhancing their toxicological and optical properties. Using a miniCAST, this study produced BC at six oxidation states. HPLC-DAD-QTOF-MS and LC-MS/MS technologies were employed to characterize the organic coatings on BC and investigate the associated chromophores and metabolomics effects on Hela cells. The chemical compositions of SOA organics resembled those in ambient air. Interestingly, greater BC maturity did not correlate with increased light absorption. Intermediate maturity showed the strongest absorption, with common chromophores but higher intensities. Aliphatic and polyaromatic compounds were the primary absorbers, with C 21 H 41 O 6 and C 24 H 50 N 2 O 4 as the strongest chromophores in ESI+ mode, and C 16 H 32 O 2 and C 10 H 7 NO 3 in ESI- mode. Metabonomics and pathway analysis revealed down-regulation of 13 metabolites involved in lipid synthesis in cells exposed to different SOA organics. Plasmalogen, triacylglycerol, and cardiolipin pathways were significantly influenced. Plasmalogens emerged as potential therapeutic targets for neurodegenerative and cardiometabolic diseases, and cardiolipin, a crucial mitochondrial phospholipid for cellular energy production, indicating that reduced metabolites due to SOA organics disrupt cellular lipid homeostasis and alter normal cellular functions. [Display omitted] • Coating components generated by miniCAST and real combustion exhibited similarity. • Aliphatic and polyaromatic compounds were identified as the primary absorbers. • Higher maturity of fresh BC does not link to increased light absorption. • BC coatings impact cellular lipid homeostasis and normal cellular functions. • Three biological pathways involved in lipid synthesis were significantly affected. [ABSTRACT FROM AUTHOR]

Light-absorbing carbonaceous aerosols primarily comprise black carbon (BC) and brown carbon (BrC), and they play a key role in atmospheric radiative forcing and global climate. Here, we present the light absorption, potential sources, and health risks of BC and BrC during the prescribed burning season at an urban background site in Brisbane based on the measurements with a seven-wavelength aethalometer. The enhancements in light absorption at 880 nm were potentially governed by the transport of prescribed burning emissions. Source apportionment results revealed that fossil-fuel (FF) combustion contributed more to the total equivalent BC (eBC) (67%) over the entire measurement period as compared to biomass burning (BB). The percentages of secondary BrC to BrC for BB- and FF-dominated periods were 60% and 21%, respectively, indicating the greater potential of BB emissions to form secondary BrC compared to FF emissions. The diurnal trend showed that the peaks of secondary BrC occurred at nighttime with high relative humidity, implying that the formation of secondary BrC was potentially associated with aqueous reactions. Potential source contribution function (PSCF) results suggested that air masses originating from southern and northern Brisbane were the potential pollution sources, where BB and traffic emissions were dominant. In addition, the health risks of eBC (based on equivalent numbers of passively smoked cigarettes) remarkably increased for periods with elevated eBC emissions, potentially originating from prescribed burns. These findings contribute to our understanding of the impact of BB on the light absorption properties of BC and BrC and could serve as a reference for government officials when performing prescribed burns with reduced environmental and health effects. • The light absorption of BC and BrC was studied during the prescribed burning season at an urban background site in Brisbane. • Primary BrC dominated the total light absorption of BrC in Brisbane. • Biomass burning emissions were associated with the light absorption of primary and secondary brown carbon. [ABSTRACT FROM AUTHOR]

Previous studies have revealed that the light absorption effect of black carbon (BC) aerosol could influence ozone concentrations via absorbing sunlight and modulating photolysis rates, the so-called aerosol-photolysis interaction (API). However, few studies have quantified the API effect of organic carbon (OC) aerosol, which has recently been found to contribute to about 10%–40% of the total light absorption at 300 nm wavelength. This study tried to quantify and compare the OC and BC aerosols' influence on ozone concentrations through a case study over North China Plain (NCP) in Oct. 2018. By modulating OC's absorption index based on field measurements, we quantified the OC and BC API effect on surface ozone by the WRF-Chem model. The API effect and its uncertainties of OC aerosols were evaluated using the high and low absorption values that have been reported in previous studies. Results showed that, in terms of the pollution periods in NCP, removing all the OC aerosol from the atmosphere could increase the daytime maximum daily average 8-h (MDA8) O 3. In this episode, the average (extreme) MDA8 O 3 increased by 0.7–2.4 ppb (1.1–3.7 ppb), accounting for 1.5%–5.3% (2.4%–8.8%) of ozone concentration, comparable to that by BC of 2.0 ppb (3.3 ppb), accounting for 4.4% (7.8%), which means the OC's API effect was 35%–120% of BC's API effect on surface ozone in this case. The results also indicated a fact that, though OC has a lower light absorption rate than BC, the API efficiency of OC on surface ozone when reducing aerosols could be compensated by a higher portion of OC aerosols and higher light absorption efficiency due to much more OC was distributed on higher altitude (especially 1–3 km) than BC aerosols, which result in larger ozone changes in both the low troposphere and surface. [Display omitted] • OC reduction led to ozone deterioration via aerosol-photolysis interaction (API). • OC's API effect on ozone is comparable to that of BC with large uncertainties. • OC at higher altitudes has higher efficiency in affecting surface ozone. [ABSTRACT FROM AUTHOR]

Volatility and effective density of aerosol particles are complicatedly linked properties, undergoing dynamic temporal evolution in the ambient environment. However, the simultaneous investigation of these physicochemical characteristics remains unexplored in roadside environments that exhibit a significant proportion of motorcycles in the vehicle fleet - a common scenario in Southeast Asia. As such, we deployed an innovative in-situ measurement technique, specifically the Volatile Tandem Differential Mobility Analyzer and Aerosol Particle Mass Analyzer (VT-DMA-APM) system, to investigate ultrafine particles (UFPs) in an urban region of northern Taiwan. Our findings revealed that the UFPs predominant in this study area were largely soot aggregates interspersed with condensable materials. Traffic-related air pollutants (TRAPs), specifically condensable organic substances, emerged as key determinants of particle effective density and volatility. Intriguingly, the peculiar interrelation between aerosol physicochemical properties and particle size suggests that UFPs may represent an amalgamation of black carbon (BC) coated with condensable substances and non-BC-containing particles. We observed an inverse relationship between effective density and volatility, indicative of atmospheric aging processes. Moreover, concurrent measurements of Absorption Angstrom Exponent (AAE) and shape factor (Ks) provided valuable insights into variations in optical properties and morphology during aging. Peak AAE and minimal Ks values consistently occurred at noon, implying heightened particle aging during this period due to coating and morphological alterations. [Display omitted] • Revealed traffic emissions as a key influencer on UFP's effective density. • Low-volatile compounds identified as aged materials, revealing aging degree. • Demonstrated correlation between particle aging and optical/morphological changes. • Linked UFP size-dependency in relation to volatility and density patterns. [ABSTRACT FROM AUTHOR]

The mass concentration, size distribution and mixing state of refractory black carbon (rBC) particles, together with other pollutants and meteorological variables, were observed at a station with a height of 528 m above ground to understand source of rBC particles over Beijing. Here we present observational evidences that regional transported rBC is an important source of rBC in high layer over Beijing. In our observations, the mass concentration of rBC increased from 1.0 μg m−3 to 4.6 μg m−3 during period with strong regional transport of pollutants, but decreased to 1.8 μg m−3 when regional transport weakened. Such trend was different with local emitted NO x , but consistent with regional transported SO 2. Further analyses indicated that the transported rBC particles were highly aged; the ratio of "thickly" coated rBC in total rBC (f BC) increased from 52.4% to 71.3% during period with strong regional transport, and then decreased slightly to 66.9% when regional transport weakened, likely caused by supplement of freshly emitted local BC particles. The aged rBC particles own enhanced light absorbing capacity, which may exert more important role in weakening atmospheric diffusion capacity and aggravating surface haze pollution, and hence should be concerned in future pollution mitigation. • Regional transported rBC is an important source of rBC in high layer over Beijing. • The transported rBC in high layer is highly aged. • The aged rBC owns enhanced light absorbing capacity. [ABSTRACT FROM AUTHOR]

Black carbon (BC) particles over the Qinghai-Tibet Plateau (Q-TP), whether suspended in the air or deposited on snow, can affect snow melt and accelerate glacier retreat. Since BC over the Q-TP may originate from different regions, it is necessary to understand the transport mechanism of BC and then provide concentrations and spatial-temporal distributions of BC over Q-TP, in order to study its radiative and climatic effects. In this study, Weather Research and Forecasting model with Chemistry (WRF-Chem), with MIX emission inventory (a mosaic Asian anthropogenic emission inventory for the MICS-Asia and the HTAP projects), was used to study the BC transport from South Asia, one of the major BC source regions, to Q-TP in April (pre-monsoon season), July (summer monsoon season) and December (winter monsoon season). The model's ability to simulate the BC transport from South Asia to the Q-TP was firstly evaluate using various reanalysis data, including 2 m temperature, precipitation, 10 m wind speed and direction and BC concentration at surface. The simulated meteorological fields and seasonal distribution and variation of BC are generally in good agreement with reanalysis data. The model showed good performance in simulating transport of BC as well. Our study showed that during pre-monsoon season, BC aerosols accumulated in the foothills of the Himalayas and were transported to southern Q-TP and even Southeast Asia via dry and wet deposition and westerly winds below 200hpa. Although the cyclonic airflow, which was favorable to transport, prevailed in South Asia, slight BC aerosols would be transported to Q-TP through wet deposition due to the efficient wet scavenging by abundant precipitation during summer monsoon season. During winter monsoon season, the prevailing westerly winds at 500hpa would transport BC aerosols from South Asia to Q-TP by dry deposition. A sensitivity simulation using PKU emission inventory (Peking University's global BC emission inventory) was then conducted to investigate the impact of different emission inventory on the modeling results. It is shown that the simulations using the different BC emission inventories overall did not have significant impacts on spatial distributions of surface concentration and column burden during three studies seasons. However, the simulated BC concentrations and burden based on PKU were overall higher than that based on MIX, that is, main differences were found in the southern part of Q-TP (i.e. adjacent to South Asia), especially during pre-monsoon and winter monsoon seasons. The differences of mean BC surface concentration ranging from 0.1 to 1 μg/m3, and burden ranging from 0.1 to 1 mg/m2 due to both higher dry and wet deposition (0.1–2 μg/m2/s for dry deposition flux, and 0.1–3 μg/m2/s for wet deposition flux) during pre-monsoon. During winter monsoon seasons, relatively large differences (0–3 μg/m3 for concentration, and 0–2 mg/m2 for burden, and 0.1–3 μg/m2/s for dry deposition flux) were found in southern Q-TP. • By using different emission inventories, MIX and PKU, WRF-Chem model is used to simulate transport of BC. • The simulations using the different BC emission inventories may not have significant impacts on spatial distributions of surface concentration and column burden. • The major differences of BC by using MIX and PKU are located in South Asia and Southeast Asia while relatively small over Q-TP. • The transmission of BC is mainly influenced by large-scale atmospheric circulation. [ABSTRACT FROM AUTHOR]

In the past few decades, forest fires have increased in number and severity, especially in the Mediterranean regions of Türkiye and Greece, where significant fires caused damage to thousands of hectares of land as well as wildlife. The main objective of the present study is to develop an emission estimation method with satellite-based burned area data from significant forest fire events in the Eastern Mediterranean in July–August 2021. In the first stage of this study, pre-fire and post-fire images of the study area acquired by the Sentinel-2 satellite were processed to calculate the normalized burn rate difference index (dNBR). Then, CORINE Land Cover (CLC) data were used for detecting land cover classes in the burned areas. Atmospheric emissions of NO x , CO, SO 2 , total suspended particulate matter (TSP), particulate matter with diameters that are equal to or smaller than 2.5 μm (PM 2.5), and black carbon (BC) were estimated using the EMEP/EEA Tier 2 - technology-specific approach method, in which burned area maps were retrieved using Sentinel-2 imageries and later combined with land cover type and burning efficiency to estimate the quantity of burning biomass emissions. Emission factors were then used to estimate the fires' trace gas and aerosol emissions. The results showed that the highest burned areas were found in the western Mediterranean region in Türkiye and Central Greece (⁓50,000 ha). The atmospheric emissions from these fires were calculated to be similar in both countries. Furthermore, emission amounts were compared with three different global fire emission inventories including GFAS, GFED, and FINN. The emissions obtained from the GFAS database were the highest emissions of the four emission estimation approaches and our estimated emissions were close to the GFAS. Emissions calculated from the other two databases (FINN and GFED) mostly provided underestimated emissions. The emission uncertainties in this study mainly originated from assumptions regarding the inclusion of burned area efficiency in emission calculations, the landcover dataset, and the emission factors used. Overall, this study is considered a new approach to emission calculations using Sentinel-2 data. This research provides further insight into the use of Sentinel-2 data in emission calculation applications at the local to regional scales. [Display omitted] • Emission estimations for catastrophic fires over the Eastern Mediterranean were developed. • The proposed new approach simultaneously uses fire severity and land cover data. • VIIRS and MODIS active fire data for the progression of individual fires are used. • The western Mediterranean region in Türkiye and Central Greece was mostly affected. • Calculated total emissions were close to the emissions from the GFAS, but significantly different from the GFED. [ABSTRACT FROM AUTHOR]

The complex microphysical characteristics of black carbon aerosol (BC) results in large uncertainties in the evaluation of BC's climatic and environmental effects. In this study, the microphysical properties were investigated in fresh BC emitted from traffic sources (gasoline vehicle and diesel) and aged BC emitted from solid fuel burning sources (coal, cotton stem, rice stem and mulberry). For the BC core size distribution, the number size distribution of traffic sources peaks at a lower value than that of aged solid fuel burning sources. Although traffic sources emit a greater number of small BC cores, traffic sources could also emit BC aerosols with large BC cores (diameter larger than 400 nm) not found in solid fuel sources. The coating thickness of BC from traffic sources is significantly lower than that of aged BC from solid fuel sources. Such differences in size distribution and coating thickness cause large variations in other microphysical parameters, such as light absorption and hygroscopicity, for these two types of BC. The mass absorption cross section (MAC) of aged BC from cotton stems reached 11.69 m2/g, nearly 2 times higher than the MAC (6.08 m2/g) of fresh BC from gasoline vehicles. The hygroscopicity of aged BC from solid fuel burning is also much higher than that of fresh BC from traffic. The critical supersaturation needed to activate BC to become cloud droplets is 0.03% for the former and 0.42% for the latter. This study reports the BC emission characteristics of traffic sources and emphasizes the large property difference between fresh traffic emission BC and aged solid fuel burning BC. The microphysical properties of BC should be carefully considered to better resolve BC concentrations and optical properties in climatic models. • BC number size distribution from traffic peaks at lower value than that from solid fuel burning. • The absorption ability of aged BC from solid fuel burning could be nearly two times higher than that from traffic. • The effective density of aged BC exhibited a unimodal pattern peaking at 0.9–1.4 g/cm3. [ABSTRACT FROM AUTHOR]

Due to the COVID-19 pandemic, lockdown restrictions were established around the world. Many studies have assessed whether these restrictions affected atmospheric pollution. Comparison between them is difficult as the periods of time considered are generally not the same and thus, different conclusions may be reached. Besides, most of them consider mean daily pollutant concentration, despite differences being observed according to the time of day. In this study, the hourly levels of PM10, PM2.5 and black carbon (BC) in an industrial suburban area in the north of Spain were analysed from May 2019 to June 2020 and compared with those from the literature, using the same period in each case. In general, the highest concentrations were reached when the wind direction came from the southwest (where a steelworks, a coal-fired power plant and other industries are located) and during the night-time, both before and during the lockdown. The highest concentrations of PM10, PM2.5 and BC were observed from December to February (on average: 45, 17 and 1.3 μg m−3, respectively). The decrease/increase in those pollutants levels during the lockdown were found to be highly dependent on the period considered. Indeed, PM10 can be found to decrease by up to 39% or increase by 12%; PM2.5 can decrease by 21% or increase by up to 36%; and BC, although it generally decreases (by up to 42%), can increase by 7.4%. [Display omitted] • Hourly levels of pollutants were jointly analysed with wind direction and speed. • The highest levels of PM and black carbon were found during night hours. • SW winds associated with high levels, pointing to industries in that direction. • The lockdown period considered affects the conclusions on the level variations. • PM10 may vary by −39% or 8.7%; PM2.5 by −21% or 31% and BC by −42% or 7.4%. [ABSTRACT FROM AUTHOR]

Analyses of black carbon (BC) data from three different environments in India - Delhi megacity, Srinagar metropolitan and Gulmarg hill station, showed that Delhi had the highest annual average BC concentration (12.3 ± 10.2 μg m−3), followed by Srinagar (4.3 ± 5 μg m−3) and Gulmarg (2.4 ± 2 μg m−3). The inflow of aerosols from the neighboring agricultural regions, notably during Winter, causes Delhi to have the highest seasonal average BC (16.8 μg m−3). Srinagar had the highest average seasonal BC during autumn (6.3 μg m−3) due to the burning of horticulture residue and hardwood for charcoal making and residential heating. At Gulmarg, on the other hand, the winter season's high BC (2.2 μg m−3) is due to the increased emissions from the tourist traffic, snowmobile/ATVs and wood burning for residential heating. BC concentrations in Delhi and Srinagar were roughly in line with their population size. However, compared to sites with the similar population, BC at Gulmarg was roughly twice higher than the other sites. There was a higher contribution to BC from fossil fuels than biomass burning at all three sites, which indicates that cars are the primary source of BC. Overall, values of BC aerosol optical properties in Delhi are much higher than those in Srinagar and Gulmarg. During the cold season, continental air masses transport BC from the neighboring areas to Delhi and westerlies enhance the local BC loading at Srinagar and Gulmarg. The predominant presence of absorbing aerosols, particularly BC, during late autumn and winter at all three sites leads to an increase in aerosol optical depth (AOD), a reduction in single scattering albedo (SSA) and an increase in asymmetry parameter (AP). As a result, there is a significant increase in the radiative forcing of the atmosphere (RF ATM), with the highest values observed in January in Delhi (+71.5 W m−2) and Srinagar (+56.05 W m−2), and in November at Gulmarg (+18.5 W m−2). These findings suggest that small rural towns that are affected by seasonal emissions, low planetary boundary layers, and frequent temperature inversions, can contribute to a substantial amount of radiative forcing. This study provides a larger perspective on increasing BC in Delhi, and urban-rural fringe areas in the Indian Himalayas, which is crucial for identifying what actions must be taken to control BC emissions to reduce impacts on cryosphere, human health and other sectors. [Display omitted] • Contrasting locations in urban-rural fringe areas of the Indian Himalayas and IGP – Delhi, Srinagar & Gulmarg. • Difference in seasonal and diurnal patterns was observed in BC between urban and rural sites. • The RF ATM in Srinagar comparable to metropolitan Delhi during winter due to biomass and coal burning. • BC concentrations in Gulmarg were twice those in other sites with the same population. • Significant contribution from rural town with seasonal emissions, low PBL, and frequent temperature inversions. [ABSTRACT FROM AUTHOR]

Atmospheric loading of black carbon aerosols influences air quality and visibility, and their mixing state and aerosol chemistry were sensitive to both emission scenarios and regional transport. In this study, the aerodynamic size-resolved mixing state of refractory black carbon aerosols (rBC) was investigated using a novel tandem system consisting of an aerodynamic aerosol classifier (AAC), a single particle soot photometer (SP2), and single-particle-aerosol mass spectrometry (SPA-MS) during the XXIV Olympic Winter Games (OWG) at an urban site in Beijing. Particles with aerodynamic diameter (D ae) of 200 nm and 300 nm were selected by AAC to focus on the effect of relative differences in morphology on the coating thickness, coating compositions, and optical properties of rBC particles. We found that rBC-containing particles with D ae of 300 nm were characterized by a rBC core with a count median diameter (CMD) of 108 ± 4 nm that typically have regular morphology (χ : m e a n ∼ 1) , higher relative coating thickness (RCT: mean ∼1.9), and strong light absorption enhancement (E abs : mean ∼1.5). The rBC-containing particles with D ae = 200 nm normally had irregular shapes (χ : m e a n ∼ 1.4) and weak E abs (E abs : mean ∼1.37). Classification based on air mass clustering and air pollution level revealed that the coating thickness of rBC particles only exhibited unimodal patterns under clean air conditions and distinct bimodal distributions under heavy pollution conditions, implying multiple origins of rBC particles, even during OWG periods. The coating thickness and E abs of rBC particles were greater when influenced by the higher RH air from east. Furthermore, the chemical compositions of the rBC coating quantitatively determined by SPA-MS were used to estimate the possible origins of the D ae = 300 nm, featured by a thicker coating thickness and stronger light absorption enhancement. Our results showed that rBC particles were primarily mixed with organics, nitrate, and sulfate during the XXIV OWG period. The organic components have a limited role in increasing rBC coatings under polluted conditions, while the alkali metal ions (K and Na) associated with traffic emissions and the secondary inorganic species favor the formation of thick coatings. Higher RH makes limited contributions to rBC mixed with sulfate and organics only (BCOC*_S) and pure BC. The relatively fresh BC could directly mix with organics and sulfate at low RH levels while evolving to mix with nitrate at high RH conditions. In addition to high concentrations of locally emitted precursors and high RH that tend to form thick coatings of nitrate-related rBC aerosols, secondary transport from the west and southwest also contributes to rBC aerosols mixed with nitrate with relatively thick coatings. • rBC with an aerodynamic diameter (D ae) of 300 nm typically have regular morphology. • rBC of regular shape(D ae = 300 nm)has thicker coatings and stronger absorption enhancement. • During the OWG, rBC particles were primarily mixed with organics, nitrate and sulfate. • rBC particles had multiple sources, even in the OWG periods. • The organic components have a limited role in increasing rBC coatings under polluted conditions. [ABSTRACT FROM AUTHOR]

Vehicles are a major source of anthropogenic emissions of carbon monoxide (CO), nitrogen oxides (NO x), and black carbon (BC). CO and NO x are known to be harmful to human health and contribute to ozone formation, while BC absorbs solar radiation that contributes to global warming and also has negative impacts on human health and visibility. Travel restrictions implemented during the COVID-19 pandemic provide researchers the opportunity to study the impact of large, on-road traffic reductions on local air quality. Traffic counts collected along Interstate-95, a major eight-lane highway in Maryland (US), reveal a 60% decrease in passenger car totals and an 8.6% (combination-unit) and 21% (single-unit) decrease in truck traffic counts in April 2020 relative to prior Aprils. The decrease in total on-road vehicles led to the near-elimination in stop-and-go traffic and a 14% increase in the mean vehicle speed during April 2020. Ambient near-road (NR) BC, CO, NO x , and carbon dioxide (CO 2) measurements were used to determine vehicular emission ratios (ΔBC/ΔCO, ΔBC/ΔCO 2 , ΔNO x /ΔCO, ΔNO x /ΔCO 2 , and ΔCO/ΔCO 2), with each ratio defined as the slope value of a linear regression performed on the concentrations of two pollutants within an hour. A decrease of up to a factor of two in ΔBC/ΔCO, ΔBC/ΔCO 2 , ΔNO x /ΔCO 2 , and in the fraction of on-road diesel vehicles from weekdays to weekends shows diesel vehicles to be the dominant source of BC and NO x emissions at this NR site. We estimate up to a 70% reduction in BC emissions in April 2020 compared to earlier years, and attribute much of this to lower diesel BC emissions resulting from improvements in traffic flow and fewer instances of acceleration and braking. Future efforts to reduce vehicular BC emissions should focus on improving traffic flow or turbocharger lag within diesel engines. Inferred BC emissions from the NR site also depend on ambient temperature, with an increase of 54% in ΔBC/ΔCO from −5 to 20 °C during the cold season, similar to previous studies that reported increasing BC emissions with rising temperature. The default setting of MOVES3, the current version of the mobile emission model used by the US EPA, does not adjust hot-running BC emissions for ambient temperature. Future work will focus on improving the accuracy of mobile emissions in air quality modeling by incorporating the effects of temperature and traffic flow in the system used to generate mobile emissions input for commonly used air quality models. • Diesel trucks are the dominant source of BC and NO x emissions in Maryland (US). • In April 2020, interstate highway car counts fell by ∼60% and trucks by ∼15%. • Mean vehicle speed increased by 14% and stop-and-go traffic was nearly eliminated. • Improved traffic flow reduced BC emissions from diesel trucks by about 70%. • BC emissions are also sensitive to temperature, increasing by ∼50% from −5 to 20 °C. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols emitted from incomplete combustion of fossil fuels, biofuels, and biomass have significant effects on the environment and human health. Combustion-derived BC aerosols are an important component in haze pollution. High concentrations of BC aerosols were found in fine particulate matter (PM 2.5) in China, and source apportionment was the strategy underpinning targeted mitigation actions. Here, we present a Bayesian statistical model, a three-dimensional array of a stable carbon isotope (δ13C) and the ratios of non-sea-salt K+ to BC (nss-K+/BC) and ΔBC/ΔCO that is a reasonably inexpensive and rapid way to constrain BC source apportionments. This study analyzed 551 daily PM 2.5 samples collected in January 2018 in 18 large cities and at 1 remote site scattered across China. The results show that BC concentrations were generally higher in cities in northern China than they were in cities in southern China. Source apportionments indicate that BC in 44% of cities was mainly from liquid fuel combustion. In other sites, including 39% of cities, one suburban site, and one remote site, BC was mainly from biomass burning. These findings suggest that to improve air quality, the Chinese government should further strengthen controls on liquid fuel combustion and consider controlling biomass burning. • Using δ13C, K+/BC, and ΔBC/ΔCO, to identify black carbon sources across China. • Black carbon was mainly from liquid fuel combustion in 44% of the large cities in China. • Biomass burning was also an important source of black carbon. [ABSTRACT FROM AUTHOR]

Aerosols over the Tibetan Plateau (TP) play an important role in the regional and global climate change and ecological environment. The Second Tibetan Plateau Scientific Expedition and Research Program (STEP) carried out observation experiment at the Nam Co Station for Multisphere Observation and Research, Chinese Academy of Sciences (Nam Co Station, 30°46′N, 90°59′E, 4730 m) in the central TP from August 5 to September 11, 2020. This paper investigated the aerosol optical properties and its potential sources over Nam Co region. The main results are as follow: the average aerosol optical depth was 0.025 during the observation period; the average black carbon (BC) concentration and aerosol number concentration was 37 ng/m3 and 129 N/cm3, respectively; the diurnal variation and vertical distribution of aerosol were affected by the local meteorological elements. Frequent southerly winds during the summer monsoon led to a certain contribution of South Asia to the BC concentration in Nam Co region. And particles from the Taklimakan Desert led to dramatic increasing of aerosol number concentration over Nam Co region. The aerosol optical characteristics and influencing factors over the central TP were analyzed, which is beneficial to further study the influence of aerosols over the TP on regional and global weather and climate. • Optical properties of aerosol over Nam Co station were observed by the STEP of China. • Nam Co region was generally influenced by BC from South Asia, local pollution emissions and north particles. • The average of AOD, depolarization ratio and BC over Nam Co station was 0.026, 0.033 and 37 ng/m3, respectively. [ABSTRACT FROM AUTHOR]

A mobile monitoring campaign was conducted (by bicycle) to assess the black carbon (BC) concentrations in Cluj-Napoca city, Romania, in 2020, before, during and after COVID-19 lock-down. Over the entire study period, the BC concentrations ranged between 1.0 and 25.9 μg/m³ (averaged per street section and period characterized by different traffic conditions). Marked spatial and temporal differences were observed. Observed differences in BC concentrations between locations are attributed to traffic intensities, with average BC concentrations, under normal circumstances, of 6.6–14.3 μg/m³ at roads with high to intense traffic, compared to 2.8–3.1 μg/m³ at areas with reduced traffic, such as residential areas, parks and pedestrian streets. The COVID-19 measures impacted traffic volumes, and hence average BC concentrations decreased from 5.9 μg/m³ to 3.0 μg/m³ during lock-down and in a lower extent to 3.4 μg/m³ and 4.4 μg/m³ in post-lockdown periods with reduced and more normalized traffic. Two approaches to account for variations in background concentrations when comparing different situations in time are assessed. Subtracting background concentrations that are measured at background sites along the monitoring route is an appropriate method to assess spatio-temporal differences in concentrations. A reduction of about 1–2 μg/m³ was observed for the streets with low to medium traffic, and up to 6 μg/m³ at high traffic locations under lockdown. The approach presented in this study, using mobile measurements, is useful to understand the personal exposure to BC along the roads in different seasons and the influence of traffic reduction on BC pollution during prolonged restrictions. All these will support policymakers to reduce pollution and achieve EU directives targets and WHO recommendations. [Display omitted] • Black Carbon (BC) concentration in Cluj-Napoca depend on the traffic intensity. • Traffic restriction due to COVID-19 pandemic reduced BC concentrations. • Mobile measurements can be used to assess spatial variability of BC. • Background corrections are needed to assess the impact of traffic measures on BC. • Traffic-free zones along the routes can be used for background corrections of BC. [ABSTRACT FROM AUTHOR]

Regional transport is deemed the key physical process affecting air pollution formation. Previous studies have indicated that black carbon (BC) is abundant and unevenly distributed over eastern China, but the details of its three-dimensional (3-D) distributions and sources are still lacking. In this study, based on vertical observations and by using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) coupled with the BC-tagging technique, we explored the 3-D distributions and sources of BC under two typical winter pollution events in eastern China, namely, one induced by cold front transport (TRAN) and another induced by stagnant weather (STAG). During TRAN, cold air can transport BC from upwind (North China Plain, NCP) to downwind (Yangtze River Delta, YRD) regions, thereby making the source region components of BC more diversified over the YRD than during STAG. It also significantly increased the proportion of BC residential sources in the YRD. The higher the altitude is, the higher the ratios of BC sources originating from long-range transport are. In TRAN, except for horizontal advection, which plays a key role in the distribution of BC, a stronger vertical advection changes the BC profiles and raises the boundary layer height as the cold front moves through. In particular, high-concentration BC from regional transport arrives earlier at the upper BL of downwind regions than at the surface, thus exerting a distinct positive vertical mixing effect on the surface BC. This study implies that regional transport can significantly impact BC evolution and further affect meteorology and climate on a large scale. • Regional transport was the key process of BC's 3-D structure over eastern China. • Regional transport modulated the sectoral source distribution of BC in the downwind region. • BC from regional transport arrived earlier at the upper BL of downwind regions than at the surface. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is one important component contributing to global warming and its climate-related impacts strongly depend on mixing state. Previous observations at ground level indicated BC aging was at a fast rate in daytime with efficient photochemical reactions, while BC aging significantly weakened at night. Here we present evidences that BC aging still occurs efficiently at night in the residual layer (RL). The ratio of "thickly" coated refractory BC (rBC) in total rBC (f BC) increased from 51.3% at 00:00 LST to 61.5% at 07:00 LST at the CITIC station, which located in the RL at night, with an increasing rate of 1.4% per hour. Such an increasing rate was even higher than that during noontime (11:00 to 15:00 LST, 0.7% per hour). Similar trend also reflected in the coating thickness (D p /D c) of rBC particles, which increased from 1.52 at 00:00 LST to 1.63 at 07:00 LST. The aging of rBC in the RL at night enhances light absorption of rBC particles correspondingly; calculated absorption enhancement (E abs) increased from 1.64 at 00:00 LST to 1.79 in at 07:00 LST. Further analysis indicated that the E abs depends not only on the D p /D c of rBC particles, but also on its size. An increase in the size of rBC particles in polluted episode can also enhance the E abs. Combined observations of development of boundary layer and pollutants at the CITIC station suggested that rBC particles were upwards transported in daytime and trapped in the RL at night, where they were aged efficiently. These results will improve our understanding on rBC aging in the atmosphere, and hence help to evaluate its radiative forcing. • We present evidences that BC aging still occurs efficiently at night in the residual layer. • The increasing rate of f BC in the RL at night (1.4% per hour) was higher than that in daytime (0.7% per hour). • The aging of rBC in the RL at night enhances its light absorption. [ABSTRACT FROM AUTHOR]

The aims of this review are: analyse the in-vehicle exposure determinants to traffic-related air pollutants (TRAPs); identify the lack of information in this field, providing suggestions for future surveys; discuss the applicability of innovative solutions for the reduction of in-vehicle exposure to TRAPs. outlined that route, traffic and time-related variables are closely related to each other and mainly affect the in-cabin black carbon, carbon monoxide, particulate matter and ultrafine particles exposure levels. Self-pollution plays an important role in defining the in-vehicle exposure especially to volatile organic compounds. Ventilation settings resulted to be the main determinants of in-vehicle exposure to TRAPs. One of the gaps of knowledge identified concerns the impact of leading vehicles on in-cabin TRAPs concentrations. The study of in-cabin exposure determinant factors is useful to implement effective measures to mitigate high exposures inside vehicles: the most promising seems to be the development of responsive ventilation systems. [Display omitted] • Route, time and traffic characteristics are closely related to each other. • Self-pollution plays a critical role in defining the in-cabin pollutants exposure. • Ventilation settings is the main determinants of in-vehicle exposure to TRAPs. • Gaps of knowledge: impact of leading vehicles on in-cabin TRAPs concentrations. • Gaps of knowledge: factors associated to in-vehicle exposure to VOCs. [ABSTRACT FROM AUTHOR]

This work use observed and modeled data to trace a basic model that describes how the bulk chemical composition can be used to determine the aerosol size-dependency of hygroscopicity inside the urban aerosol pollution plume from Manaus, Brazil. The procedure is then used to predict the Cloud Condensation Nuclei (CCN) concentration (N C C N) from the Aerosol Size Distribution (ASD). The work briefly described hourly averaged data of ASD, Black Carbon size distribution (BCSD), Black Carbon mass concentration (BC), N C C N , and aerosol size hygroscopicity (κ) observed about 70 km downwind of the City of Manaus, inside the amazon rain forest, during 60 days of 2014, in the course of the rainy season. It uses a description of aerosol chemical composition obtained previously in the city of São Paulo, Brazil, as starting point to formulate a model that describes how particles in the pollution plume act as CCN as a function of their sizes and bulk chemical composition. A parameterization based on a polynomial fitting is proposed to determine BCSD from the BC. The measured and parameterized BCSD agree very well with more than 98% of the observed BCSDs, presenting a correlation coefficient larger than 0.9 with observation. The parameterized BC number concentration is also very well represented, with a correlation coefficient of 0.91 and a slope of 0.99 in comparison with observations. This work also studies how soot particles are incorporated in the CCN population and propose a parameterization to represent it. Simulations suggest that the larger BC particles are only partially incorporated as CCN and BC is a constraint to the fraction of aerosols that can act as CCN in all size ranges. The simulations also suggest that the incorporation of BC as CCN is probably only effective through coagulation in the presence of the wet phase. In addition, the work compares different strategies to predict observed N C C N from ASD. It is shown that the strategy presented can substantially improve the results of comparison of modeled and measured data from as bad as 2.14 ± 0.65 to as good as 1.02 ± 0.17. This study shows that the knowledge of the bulk chemical composition can be used to predict both the size-resolved chemical composition and mixing state, reducing the number of parameters needed to predict N C C N. • Model to define CCN activity from aerosol size distribution and chemical composition. • How soot particles are incorporated in the CCN population. • Parameterization of black carbon size distribution from black carbon mass concentration. • Comparison of different strategies to predict observed CCN concentration. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is an important component of the brown clouds, contributing to climate and health effects of air pollution. In this work, we developed a new method for measuring BC concentrations and its radiocarbon isotope (14C) using quartz wool disk passive air samplers (Pas-QW). A field calibration study was conducted at two sampling sites (Guangzhou and Yantai), using an improved thermal/optical method to measure BC. Uptake profiles of Pas-QW were linear over the 77 days that the samplers were deployed, and the average sampling rate of BC measured was 1.1 ± 0.2 m3/day. The method was found to be reproducible with coefficients of variation as low as 17% for BC measured in ambient passive samples. Furthermore, passive sampling was carried out at six sites in the Indo-China Peninsula (ICP) from January to April and June to September of 2016. The high BC concentrations and the high fraction of modern carbon (f M) values emphasizes that ICP is still dominated by biomass burning emissions (residential cooking and agricultural burning), both in dry and wet seasons. This study provides a proof concept and methodology for the application of Pas-QW to cost-effectively expand measurements of BC at the global scale. [Display omitted] • A new method for measuring BC and its 14C using quartz wool disk passive samplers. • The method requires no sample processing and have good reproducibility for BC. • The relative contribution of biomass burning to BC can reach 67 ± 13% in ICP, with obvious spatiotemporal heterogeneity. [ABSTRACT FROM AUTHOR]

Black carbon plays an important role in climate change. Whereas, accurate measurement of black carbon (also known as elemental carbon (EC)) is still a challenging issue because portion of the pyrolytic carbon produced from the organic carbon (OC) can cause the overestimation of EC when measured by thermal-optical method. As one of the remote regions in the world, the Tibetan Plateau (TP) is characterized as high OC/EC ratio in its atmosphere. In this study, potential influence of relative high OC concentration to EC were investigated at three remote sites (Yaze, Everest and Nam Co) in the TP. The results showed that carbonaceous aerosols from different sources can affect the fraction of OC extracted by methanol. Concentration of OC extracted by methanol had a significantly positive correlation with the reduction of pyrolytic carbon and EC concentrations, indicating that part of OC extracted by methanol can decrease the production of pyrolytic carbon and then reduce the overestimation of EC. After considering this effect, it is shown in this study that actual EC concentration at Yaze, Everest and Nam Co were overestimated by approximately 40.0 ± 12.6%, 28.8 ± 9.1% and 24.8 ± 4.7%, respectively. Accordingly, combined with the overestimation of EC concentration by carbonates, actual ratios of solar energy absorbed by organic carbon to EC were 1.67, 2.33 and 2.78 times those of original ones at Yaze, Everest and Nam Co, respectively. Therefore, warming effect caused by EC on the TP should be lower than that previously estimated. This phenomenon needs to be considered for both in situ study and model simulation in the future. [Display omitted] • Overestimation of EC concentration by OC in aerosols of the TP were investigated. • Fraction of OC extracted by methanol was affected by the sources of aerosols. • EC concentration overestimated by OC of aerosols at Yaze was up to 40.0%. • Fraction of solar energy absorbed by OC relative to EC was underestimated. [ABSTRACT FROM AUTHOR]

Refractory Black carbon (rBC) emitted from the combustion of biomass and fossil fuels plays an important role in the climate system. In this study, we established a record of the rBC concentration spanning 1932–2013 from an ice core retrieved from the Chongce ice cap of the West Kunlun Mountains in the western Tibetan Plateau. The record showed an increasing trend since the 1980s. The mean concentration of rBC was 2.66 ng g−1 before 1980 and 5.33 ng g−1 since 1980. The significant increase since the 1980s was very different from similar records from European ice cores. An analysis of atmospheric circulation and backward trajectories suggested that former USSR, the Middle East, and South Asia were the most likely source regions for the rBC deposited at the Chongce ice cap. This conclusion was also supported by the historical emission data in these regions. Phase analysis indicated that high rBC concentrations were closely associated with drought-induced biomass burning in the rBC source regions at the decadal timescale. These findings suggested that anthropogenic emissions controlled the long-term rBC trend, while the peak phases were caused from an increase of biomass burning. •Anthropogenic activity and climate change play a critical role in the rBC variations over the northwestern Tibetan Plateau. • Anthropogenic emissions since 1960s contributed more to rBC deposition. • Droughts-induced biomass burning were responsible for high rBC concentration phases. [ABSTRACT FROM AUTHOR]

Myocardial infarction (MI) is a major global contributor to disability and death. Few studies have investigated the impacts of short-term exposure to particulate matter with an aerodynamic diameter ≤1 μm (PM 1) and ≤2.5 μm (PM 2.5) constituents on MI mortality. We aimed to estimate the risks of MI mortality related to short-term exposures to PM 1 , PM 2.5 , and PM 2.5 constituents. Daily MI deaths, daily concentrations of PM 1 , PM 2.5 , PM 2.5 chemical compositions, and meteorological data in Qingdao during 2015–2019 were collected. We used a time-stratified case-crossover design fitted with a conditional quasi-Poisson regression incorporated with distributed lag model to quantify the associations between PM 1 , PM 2.5 , and PM 2.5 chemical compositions and MI mortality. Subgroup analyses were further implemented based on sex, age, and season. There were 36,235 MI deaths in Qingdao during 2015–2019. The results of single-day lagged effects showed that PM 1 (lag0 and lag1 days), PM 2.5 (lag0 and lag1 days), sulfate (lag0 and lag1 days), nitrate (lag0 day), ammonium (lag0 and lag1 days), and black carbon (BC, lag0 and lag1 days) were positively related to an elevated risk of MI death. The cumulative effects of per interquartile range (IQR) rise in PM 1 , PM 2.5 , sulfate, nitrate, ammonium, and BC concentrations lasting for three days (lag02 day) were related to excess risks of 2.5% (95% confidence interval [CI]: 0.2%, 4.9%), 2.0% (0.1%, 3.9%), 2.2% (0.3%, 4.1%), 2.0% (0.1%, 3.9%), 2.0% (0.1%, 4.0%), and 2.1% (0.2%, 3.9%) for MI mortality, respectively. Significant effects of PM 1 , PM 2.5 , sulfate, and BC exposures on excess risks of MI mortality were observed in aging subpopulations or during the cold season. Short-term exposures to PM 1 , PM 2.5 , sulfate, nitrate, ammonium, and BC were linked to elevated risks of MI mortality. These results strengthen the case for implementing policies to reduce air pollution. • The effects of PM 1 on MI mortality may be slightly higher than that of PM 2.5. • Sulfate, nitrate, ammonium, and BC exposures may raise the risks of MI mortality. • Significant effects of PM and constituent exposures were observed in aging subgroup. • Clean heating policies should cover the scope of PM 2.5 constituents in Qingdao. [ABSTRACT FROM AUTHOR]

Atmospheric Black Carbon (BC) is one of the absorbing components of solar radiation which potentially affects human health and regional climate. In the current study, BC mass concentrations were regularly observed for pre-monsoon and monsoon seasons using the seven-channel aethalometer (AE-33) over Peshawar, Pakistan. The scarcity of BC measurement in this region is critical for air quality assessment, hence providing much importance to this article for control policy recommendations. The monthly mean BC showed a maximum value of 12.1 ± 5.4 μg/m3 during March and a minimum value of 6.4 ± 3.1 μg/m3 during July. The bimodal diurnal BC concentration was observed in between 05:00–08:00 and 20:00–24:00 LST having a maximum night/day ratio of 3.4 during April. Furthermore, the weekdays BC concentration was higher than weekend days having the highest weekdays concentration during March (12.9 ± 5.6 μg/m3) and the lowest concentration during July (6.9 ±0.9 μg/m3). Moreover, BC contributed maximum of 22% to PM 2.5 during April and minimum of 7% during June. The source apportionment of BC revealed that maximum value of BC emitted from fossil fuel (BC FF) and biomass burning (BC BB) were 9.90 ± 0.50 μg/m3 and 2.61 ± 0.49 μg/m3 during March showed a clear dominancy of BC FF over BC BB emission. Further the highest percentage contribution of BC FF and BC BB were found to be 80.45% and 22.27% to total BC during May and April, respectively. Finally, the cluster trajectory analysis showed that majority of the air pollutants were due to local emission rather than long range transport. [Display omitted] • Detailed temporal analysis of BC, BC FF and BC BB were carried out. • Dominant BC concentration were observed in pre-monsoon season than monsoon season. • Fossil fuel emission was about 3 times higher than biomass burning. • Major potential sources of BC were originated from local as well as neighbor regions. [ABSTRACT FROM AUTHOR]

Delhi's post-monsoon and winter haze reduces visibility, causes health hazards, and interrupts usual routines. Multiple source apportionment (SA) studies recently apportioned sources and discussed organic and elemental PM source characteristics independently. To design effective pollution control strategies, it's important to obtain a comprehensive picture of particulate matter (PM 2.5) sources by doing SA on consolidated data that combines organics, inorganics, black carbon (BC), and metals. In this study, we tried to improve the understanding of PM 2.5 sources by performing double-PMF (D-PMF) analysis on a consolidated dataset encompassing non-refractory PM 2.5 factors, elements, and BC. Real-time instrumentation (HR-ToF-AMS, Xact, and Aethalometer) were used at two urban sites (IITD and IITMD) in Delhi during post-monsoon and winter seasons. The hourly average C-PM 2.5 (Composition based PM 2.5 is sum of NR-PM 2.5 , BC and metals) at IITD for the overall study period (1st Oct 2019 to 8th Jan 2020) was 91.9 ± 56.5 μg m−3, while at IITMD for the overall sampling period (31st Oct 2019 to 31st Dec 2019) was 105.2 ± 61.2 μg m−3. The sources identified by the double-PMF at both sites were road dust, traffic, secondary nitrate, secondary sulfate, oxidized organic aerosol (OOA), biomass burning (BB), and industrial. In contrast, fireworks were only resolved at IITD, and secondary chloride at IITMD. At IITD, the temporal variation of sources was noted between the post-monsoon, Diwali, and winter seasons. The secondary nitrate (17%, 15.8 ± 9.4 μg m−3) and BB (39.4%, 36.6 ± 43.6 μg m−3) were dominant during winter suggest the rapid-nighttime oxidation with favourable low temperature condition and increased heating activities, while OOA (33.4%, 17.2 ± 8.0 μg m−3) and secondary sulfate (12.7%, 6.5 ± 4.4 μg m−3) were dominating during the post-monsoon at IITD due to the high photochemical oxidation and long-range transport. The fireworks (22.2%, 26.6 ± 43.8 μg m−3) contributed a major fraction of sources during Diwali at IITD. For the concurrent measurement period (14th Nov 2019 to 31st Dec 2019) at both the sites, the mean hourly average concentration (C-PM 2.5) was 102.2 ± 53.2 μg m−3 at IITD and 99.7 ± 59.6 μg m−3 at the IITMD site. Secondary nitrate and secondary sulfate were prevalent at IITMD, while OOA and traffic dominated at IITD. D-PMF improved interpretation of sources such as the SO 4 _OA and NO 3 _OA contributions to industrial sources (Pb-rich and Zn-rich) indicate the possibility of sulfate and nitrate accumulation on metal-rich particles (for example, the formation of ZnSO 4 and PbSO 4). The signals of NO 3 _OA in the fireworks factor are due to the gunpowder (KNO 3), while HOA and BBOA suggest the role of burn-related organics. The elemental ratios K/Pb (17 at IITD) and K/As (137 at IITMD) in the secondary sulfate source from D-PMF further highlighted the role of coal combustion. The D-PMF results were in excellent agreement with single PMF on combined data (SC-PMF) done as a part of an extended study. [Display omitted] • Variation of combined-PM (non-refractory, BC and metals) sources using Double-PMF at two sites in Delhi in winter. • Delhi faces two extreme co-occurring pollution events - Fireworks and transported agricultural burning from nearby states. • The secondary nitrate and biomass burning dominant at IITD in winter suggest the rapid-nighttime oxidation. • OOA and secondary sulfate dominant in post-monsoon at IITD due to high photochemical oxidation and long-range transport. • A single-combined PMF on data sets from HR-ToF-AMS, Xact and Aethalometer done to compare with D-PMF results. [ABSTRACT FROM AUTHOR]

Black carbon (BC) and brown carbon (BrC) are major light absorbing components of aerosol, affecting visibility, radiative forcing balance and human health. In this study, we investigated the light absorption and radiative forcing of carbonaceous aerosol in the total suspended particle (TSP), coarse particle (PM 10 : particulate matter with an aerodynamic diameter less than 10 μm, Dp ≤ 10 μm), fine particle (PM 2.5 : Dp ≤ 2.5 μm), and nanoparticle (PM 0.1 : Dp ≤ 0.1 μm) in a rural area of Guanzhong Plain, China. Similar variations of the absorption Ångstrom exponent (AAE) of TSP, PM 10 , and PM 2.5 were observed. Lower light absorption coefficients and higher AAEs were obtained for PM 0.1 compared with other particle sizes. The direct radiative forcing (DRE) efficiency of BC decreased with size bins of TSP, PM 10 , PM 2.5 , and PM 0.1 , respectively. The DRE of BCs for all particle sizes at top atmosphere (TOA), surface atmosphere (SUF) and the whole atmosphere (ATM) were estimated. The optical properties of primary and secondary BrC (PBrC and SBrC) in PM 0.1 were further analyzed. The AAE values indicated that the light absorbing of SBrC was more wavelength dependent than PBrC in PM 0.1. The DRE of BC, PBrC, and SBrC in PM 0.1 were estimated firstly with the values of 19.9 Wm-2, 2.1 Wm-2, and 1.1 Wm-2 in the ATM, respectively. • The optical properties of BC and BrC in nanoparticle were investigated. • b abs, PBrC dominates the b abs,BrC of PM 0.1 at 370 nm account for 74%. • The DRE in the ATM of PBrC was ∼2 times higher than that of SBrC. • The DRE efficiency of BC at ATM in nanoparticle was the lowest compared with those in TSP, PM 10 , PM 2.5. [ABSTRACT FROM AUTHOR]

Many semi-volatile organic pollutants are present in the atmosphere both in the vapor and particle phases. About 50 years ago, a partition coefficient (K P) was defined as the compound's concentration in the particle phase (C part , in ng/m3 or pg/m3) divided by its concentration in the vapor phase (C vapor , also in ng/m3 or pg/m3) divided by the atmospheric concentration of total suspended particles (TSP , in μg/m3) or, more recently, by the concentration of particulate matter with aerodynamic diameters less than 2.5 μm (PM 2.5 , also in μg/m3). The original point of this term was to account for surface adsorption of pollutants to the particles, but over the years it has become apparent that absorption, particularly to black carbon (BC, also known as elemental carbon) in the particles, may also be important. This study investigates the importance of this particle term using about 3000 polycyclic aromatic hydrocarbon (PAH) concentrations measured from 1997 to 2018 (inclusive) in 24-h samples collected once every 12 days at five sites on the shores of the North American Great Lakes and using U.S. Environmental Protection Agency PM 2.5 concentrations at the same sites. Analyses of variance of the annual mean log(K P) values show significant differences for all six compounds among the five sites, which we attribute to the composition of the particles at the five sites. For example, the particles from the urban sites are likely to have higher black carbon levels compared to those from the more rural and remote sites. With an additional term for black carbon in these samples, these new ratios are similar across sites for a given compound. These results suggest that a black carbon term is useful and potentially important. [Display omitted] • Concentrations of 16 polycyclic aromatic hydrocarbons were measured in samples collected for 24 h once every 12 days from 1997 to 2018 at five sites near the Great Lakes. • Annual geometric mean ratios of six of these compounds' concentrations in the vapor and particle phases were calculated based on PM 2.5 and black carbon concentrations. • These ratios varied by a factor of ∼6 across sites when only the PM 2.5 concentrations were included. • These ratios varied by a factor of <2 across sites when the black carbon concentrations were included, suggesting the importance of this term in reducing inter-site variability. [ABSTRACT FROM AUTHOR]

Airborne meteorological and aerosol measurements have been performed in Longyearbyen (Svalbard islands) in the summer of 2018, coupling an instrumental aerosol payload with a meteorological radiosonde deployed on a tethered balloon. More than 70 vertical profiles of aerosol and meteorological properties have been recorded up to a maximum altitude of 1.2 km. As a main result, the present work provides a homogeneous gridded dataset of vertical profiles of equivalent black carbon (eBC) and nanoparticles (NP) concentrations and associated meteorological data (temperature, T, relative humidity, RH, pressure, P) to be employed for future modelling studies of Arctic pollution. Mean values (±SD) of eBC and NP below 500 m were 110 ± 10 ng m−3 and 1400 ± 400 particles cm−3, respectively. Mean values above 500 m were 150 ± 30 ng m−3 and 1000 ± 350 particles cm−3, respectively. Group medians of maximum eBC and NP concentrations in vertical profiles with temperature inversions were significantly higher than for those without inversion. The dataset has been complemented by continuous ground measurements of eBC with an average value of 208 ± 130 ng m−3 (median value 110 ± 70 ng m−3) for the entire campaign; the ground-based background (absence of local emission) eBC value was below 100 ng m−3 while maximum values were in the 1000–2000 ng m−3 range. Median eBC concentration measured at ground for 2 h before the tethered balloon launch was higher when temperature inversion was observed. The ground-based measurements, coupled with aerosol optical depth measurements, allowed for a preliminary discussion of two case studies related to high pollutants concentration events. [Display omitted] • 72 black carbon and nanoparticle aerosols have been measured in summer 2018. • Vertical profiles are influenced by local sources and long-range transport. • A homogeneous gridded dataset of vertical profiles has been generated. • Case studies of aerosol stratification at ground and black carbon from Eurasia are discussed. [ABSTRACT FROM AUTHOR]

Cloud condensation nuclei (CCN) spectra, that indicate the dependence of CCN number concentrations (N CCN) on supersaturation, are important factors in aerosol–cloud interactions. Owing to the lack of direct measurements of N CCN , calculating the CCN spectra based on conventional observational data of aerosols is important to obtain N CCN ; however, this is challenging owing to the complex relationship between aerosol properties and CCN activity. Machine learning techniques have recently been applied to estimate N CCN and found to be a promising method for CCN prediction. In this study, the random forest (RF) model was applied to predict CCN spectral parameters using the observation data measured in four campaigns in the North China Plain, and the effects of chemical and optical properties of aerosol on the estimation of CCN spectra were investigated. The results show that the RF model trained with the data of one campaign can be used to estimate CCN spectral parameters in another campaign, with the coefficient of determination between the estimated and measured CCN spectral parameters being approximately 0.5. The deviations of the estimation by the RF model may result from the difference in both the aerosol properties and measurement uncertainties among different campaigns, whose influence on the deviations can be further magnified by overfitting the RF model. Further analysis revealed that the major aerosol properties among the input variables of the RF model were the mass concentration of black carbon and aerosol hemispheric backscattering fraction at a wavelength of 450 nm. In addition, the roles of chemical compositions of aerosol in estimating CCN spectra parameters are different among different campaigns because the poor correlation between aerosol chemical compositions and CCN spectra parameter can affect the performance of the RF model. For estimating CCN spectra, using aerosol optical properties, including the hemispheric backscattering fraction and absorption coefficient, as model inputs is more recommended than using aerosol chemical properties. • Random forest model is used to estimate CCN spectra based on observation data in the North China Plain. • Mass concentration of black carbon and hemispheric backscattering fraction are the most important input variables. • Aerosol optical properties data are recommended in estimation of CCN spectra parameters. [ABSTRACT FROM AUTHOR]

Many rail services around the world continue to use diesel as the primary fuel source and enclosed railway stations have been identified as a possible hotspot for exposure to harmful diesel exhaust exposures. Little is known about the occupational exposure to air pollution for railway station workers due to their mobility around the station and variations in station design. A detailed understanding of the concentration of black carbon (BC), a diesel exhaust tracer, inside railway stations and the factors driving occupational exposures is required to minimize occupational exposure. Real-time personal exposure to BC was measured during 60 work-shifts encompassing different roles at three large enclosed railway stations of different design in London, Birmingham and Edinburgh (UK). Sampling was conducted by the train station workers over a period of 27 days between January 2017 to October 2018. Worker shift-mean BC exposures ranged 0.6–20.8 μg m−3 but 1-min peak exposures reached 773 μg m−3, with train dispatchers experiencing the highest BC exposures. Station design, job role, and frequency of diesel trains were the main drivers of occupational BC exposure. Elevated exposures for some station workers indicate that mitigation measures to reduce their exposure should be implemented to lower the risk of occupational health impacts. These could include improving ventilation and reducing engine emissions. [Display omitted] • Station design, job role, diesel train frequency are main drivers of occupational BC exposure. • Occupational BC exposures in enclosed train stations is the highest. • Dispatchers had the highest work-shift mean exposures. • Idling diesel trains contribute to elevated occupational exposures to BC. • Elevated exposures for some job roles indicate the need of mitigation measures. [ABSTRACT FROM AUTHOR]

The Aerosol Optical Depth (AOD) and aerosol-induced radiative forcing trends inferred for the period 1995–2019 over the Arabian Peninsula region (APR) are extensively studied using the state-of-the-art Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalysis data. We examine the long-term AOD change for five major aerosol species: Dust (DU), Sea Salt (SS), Sulfate (SU), Black Carbon (BC), and Organic Carbon (OC) over the APR. The MERRA-2 AOD comparisons with surface measurements show that it is capable to reproduce the AOD features over APR. The total AOD over the region shows a high value in JJA with the combined effect of DU and SU being major contributors. The total AOD over APR shows an increasing trend at a rate of ∼0.05/decade. Along with an incline in DU AOD , the anthropogenic signature on total AOD also hikes contributed mainly by the SU and OC. The increase in AOD also results in a surge in aerosol-induced atmospheric forcing (ATM) with a trend of 0.13 Wm-2 year−1 and 0.15 Wm-2 year−1 during MAM and JJA respectively. Overall, the study gives a comprehensive picture of the capability of the MERRA-2 in long-term aerosol monitoring over APR, primarily situated in the "dust-belt" region. • Variability of long-term species AOD over Arabian Peninsula Region (APR) was investigated using MERRA-2. • Highest AOD were found in JJA with dust and sulfate being the highest contributors. • The increasing AOD trend is accompanied with a hike in aerosol induced atmospheric radiative forcing (ATM). [ABSTRACT FROM AUTHOR]

High uncertainty in simulating the climate effect of black carbon (BC)-containing particles can be raised by an important parameter: light absorption enhancement (E abs), which was impacted by the morphology of BC, its mixing state with coating materials, and the aging process, etc. By a statistical approach called minimum R square (MRS), this study investigated the influence of aerosol chemical compositions on E abs with on-line observational datasets during summer (June 2018) and winter (December 2018) at an urban site in Wuhan, Central China. The E abs at 880 nm (E abs_880) showed a moderate enhancement with a mean value of 1.36 ± 0.35 in summer, which was significantly (p < 0.001) higher than that in winter (1.17 ± 0.24). A proxy defined as the mass ratio of non-refractory chemical components to BC (R BC) was used to link the thickness of BC-containing particles and aerosol chemical compositions with E abs. With the increase of R BC from 16.4 to 51.3 in summer and from 18.3 to 53.3 in winter, E abs_880 values amplified by 15.3% and 38.3%, respectively. The statistical and sensitivity analysis indicated that secondary inorganic aerosols (SIA) contributed most to E abs_880 during summer (92.6%) and winter (71.2%) in Wuhan. Given the dominant mass percentages of SIA in particle chemical compositions and their important role to E abs , reducing their precursors would benefit to alleviate the particle pollution and the warming effect of BC synergistically. The comparison of E abs with previous studies suggested that despite the MRS method in this study had some limitations, this method can be widely used in other regions with similar datasets. • A statistical method was used to determine light absorption enhancement of BC. • Secondary inorganic aerosols contribute most to light absorption enhancement of BC in Wuhan. • Reduction of secondary inorganic aerosol is more effective to reduce light absorption enhancement of BC. [ABSTRACT FROM AUTHOR]

Biomass burning (BB) is an important source of brown carbon (BrC) and black carbon (BC), which are two key highly absorbent substances in atmospheric particles and can have a substantial positive impact on the climate radiative forcing. This study presents the light absorption properties of BC and BrC in PM2.5 during the winter in Beijing, with a discussion on the regional transportation of the light absorption of BC and BrC. Relatively high levels of the light absorption coefficient (Abs λ) of BC, BrC, and the chemical compounds were found during haze episodes. The average Abs BC at λ = 880 and Abs BrC at λ = 370 during the haze period were as high as 4.4 and 2.9 times higher than those during the clean periods. The biomass burning tracer levoglucosan was significantly correlated with Abs BC880 (R 2 = 0.53, P < 0.001), Abs BrC370 (R 2 = 0.47, P < 0.001) and Abs BC(BB) (R 2 = 0.69, P < 0.001). The average contributions of biomass burning to organic carbon (OC) and Abs BC were 33% and 48%, respectively, indicating that biomass burning was an important source of light-absorbing substances in the atmosphere. Concentration-weighted trajectory (CWT) analyses using TrajStat software also demonstrated that regional transport of biomass burning emissions from the northwestern and southwestern areas, which cover the intense fire spots from VIIRS, had a considerable influence on the light absorption properties of PM 2.5 and even haze formation in Beijing during the winter. • Fairly high levels of the Abs BC and Abs BrC found during haze episodes. • Light absorption of BrC gave equal roles to that of BC near the UV–Vis band but was dominant at visible wavelengths. • Regional biomass burning was an important source for light absorbing substance in PM 2.5 during winter in the North China Plain region. [ABSTRACT FROM AUTHOR]

Existing regulatory pollutant monitoring networks rely on a small number of centrally located measurement sites that are purposefully sited away from major emission sources. While informative of general air quality trends regionally, these networks often do not fully capture the local variability of air pollution exposure within a community. Recent technological advancements have reduced the cost of sensors, allowing air quality monitoring campaigns with high spatial resolution. The 100 × 100 black carbon (BC) monitoring network deployed 100 low-cost BC sensors across the 15 km2 West Oakland, CA community for 100 days in the summer of 2017, producing a nearly continuous site-specific time series of BC concentrations which we aggregated to 1-h averages. Leveraging this dataset, we employed a hierarchical spatio-temporal model to accurately predict local spatio-temporal concentration patterns throughout West Oakland, at locations without monitors (average cross-validated hourly temporal R 2 = 0.60). Using our model, we identified spatially varying temporal pollution patterns associated with small-scale geographic features and proximity to local sources. In a sub-sampling analysis, we demonstrated that fine scale predictions of nearly comparable accuracy can be obtained with our modeling approach by using ∼30% of the 100 × 100 BC network supplemented by a shorter-term high-density campaign. • Hourly black carbon concentration maps predicted in West Oakland in summer 2017. • Leveraged data from the intensive 100 × 100 monitoring campaign. • Advanced spatiotemporal model can produce similar results with less intensive data. • Sources and geographic features predict spatial variation in diurnal pollution. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is one of the main components of ambient particulate matter. Previous studies have suggested that BC is more toxic than PM 2.5 (mass concentration of all sub-2.5 μm particles). One possible reason for the greater toxicity is that BC is typically in a size range which penetrates easily into lung alveoli and BC particles have a large surface area due to their fractal structure. Due to these properties, toxic gaseous compounds can condensate on the surface of BC particles and then be transported effectively into human lungs, causing a large lung-depositing surface area (LDSA) of particles. In this study, we investigated the relationship between BC and LDSA concentrations in street canyon, highway, and harbour environments in the Helsinki Metropolitan area. In all the studied environments, BC and LDSA concentrations were strongly correlated. In the harbour, cases where marine traffic was considered as the main emission source, the average LDSA per BC mass was 2.4–2.7 times higher than in the road traffic environments. This result was linked to a larger lung depositing size of BC, suggesting that condensation and coagulation of other co-emitted compounds can have a major role in the lung deposition of BC. Thus, BC emissions from marine traffic can cause higher exposure of other co-emitted toxic compounds in the human lungs than the road traffic. The fraction of LDSA linked to BC emissions in the street canyon, the highway, and the harbour were 33%, 30%, and 47%, respectively, whereas the fractions of BC mass in PM 1 concentration were 14%, 14%, and 7%, respectively. The results show that BC emissions contribute much more to LDSA than to mass concentration, which indicates that the possible strong negative health effects linked to ambient BC mass concentration could be related to the high LDSA concentration. • Characteristics of LDSA investigated in a harbour and near traffic in Helsinki area. • BC emitted from marine traffic is linked to higher LDSA per mass than road traffic. • BC emissions contribute more to LDSA (30–47% of total LDSA) than to PM 1 (7–14%). • In the harbour, higher absorption Ångström exponent was connected to higher LDSA. • Health hazard of BC might be related to high LDSA and other co-emitted species. [ABSTRACT FROM AUTHOR]

In 2016 Magee Scientific AE33 Aethalometers, capable of measuring both black carbon (BC) and the contribution of biomass burning (BB), were installed at three sites in Ireland as part of the Atmospheric Composition and Climate Change (AC3) Network. The three sites (Mace Head, Malin Head, and Carnsore Point) are coastal locations on opposing sides of the country ideally located to assess typical northern hemispheric background concentrations as well as local, regional, and transboundary pollution events. The first results of the BC measurements from these stations combined with concurrent in-situ observations (meteorological parameters, carbon monoxide (CO), and particulate matter (PM 1)) are presented here. Instrument validation was conducted and a sample dryer was found to be necessary in low-pollution environments with high relative humidity. Carnsore Point receives 33% of BC from outside Ireland, despite winds only coming from the East 14% of the time, and Malin Head BC/CO ratios indicate local traffic influence. Analysis of BC and PM 1 showed the highest concentrations to the southeast of Malin Head, yet the lowest contribution of BC to PM 1. The AE33's BB source apportionment measurements show distinct seasonal variation associated with winter-time heating, but also help differentiate between local and regional pollution. • Describes the inception and validation of Ireland's black carbon network. • Elucidates frequency distribution and compares seasonal wind sectoring across the network. • Contrasts time series of biomass burning with national emission inventory submission. [ABSTRACT FROM AUTHOR]

The outbreak of SARS-CoV-2 and subsequent spread of the disease COVID-19 became classified as a pandemic in March of 2020, leading to global safety measures introduced to limit the impact of the virus. This combination of safety measures has become commonly referred to as "lockdown". The associated industry and lifestyle changes led to reductions in the anthropogenic emission of atmospheric pollutants such as black carbon (BC), which is transported from the mid-latitudes into the Arctic during the winter and spring. Measurements of BC and other anthropogenic pollutants are of increasing importance in the Arctic due to the rapid warming observed there in the past few decades. It is believed that BC has a significant role in this warming, and so understanding the Arctic's response to reduced BC emissions at lower latitudes will provide insight into how future changes might mitigate further warming. Reductions in BC have been reported worldwide, and so in this study, the impact of these reductions on BC concentrations at the High Arctic site Villum Research Station was investigated. The effect was examined from March 2020, around when global lockdowns began, to June 2020, when the Arctic haze period ended and BC levels were once again low. Firstly, the Danish Eulerian Hemispheric Model (DEHM) was used to assess this impact on BC concentrations by adjusting global anthropogenic pollution emission inventories to simulate those observed during the lockdown period and comparing the results to a similar model run with standard emission inventories. Secondly, equivalent BC data from an aethalometer at Villum Research Station were analysed, comparing the concentrations during the lockdown period to both aethalometer data from previous years and DEHM results from the lockdown period. It was found that when adjusted DEHM emission inventories were introduced from the 1st of March, the model predicted a reduction in BC concentrations beginning on the 10th of March and reached a 10% reduction by the 1st of April. This reduction fluctuated around 10% until the end of the Arctic haze period. Aethalometer data did not show any significant change from previous years, and no concentration reduction could be concluded from its comparison with DEHM results. This is likely because the predicted reduction of 10% is smaller than both the inter-annual and intra-annual variability of measured BC concentrations at Villum. • DEHM model and aethalometer used to assess effect of lockdown on Villum BC levels. • DEHM model simulated a 10% reduction in BC at Villum during April–May 2020. • Similar reductions are expected throughout the Arctic region (between 7% and 11%). • The aethalometer showed no response to the lockdown due to inherent BC variability. [ABSTRACT FROM AUTHOR]

In this study, we developed a novel land-use street view image random forest (LUSRF) model to estimate the equivalent black carbon (eBC) concentration based on land-use random forest (LURF) and street view imagery (SVI) models and compared their accuracy and precision in the urban city of Augsburg, Germany. The variables of the LUSRF model were constructed by combining LURF and SVI model variables (i.e., land-use, street scene, and meteorological factors). Stratified cross-validation (CV) was used to validate the model performance. Based on R2 and IA (Index of Agreement), LUSRF has superiority (average-R2: 0.73, average-IA: 0.91) compared to the LURF (average-R2: 0.52, average-IA: 0.81) and SVI model (average-R2: 0.68, average-IA: 0.89) in the urban city of Augsburg during the observed period. The main driving factors of the LUSRF model for BC estimation were different in heating and non-heating periods (i.e., elevation, the proportion of moving cars, and relative humidity for the non-heating period; and elevation, the proportion of building, and relative humidity for the heating period), which improves the estimation accuracy of eBC concentration and its sources. The model verification in other areas (i.e., suburban and small towns) further proved that the model has certain generalizability. Overall, the LUSRF model will provide insight for epidemiological studies in urban areas as a personal exposure assessment. [Display omitted] • Land use street view images random forest (LUSRF) model were developed. • LUSRF model were exploited for black carbon (BC) estimation. • LUSRF have superiority compared to other models with average-R2: 0.73. • LUSRF model reduced average 10–15% estimation error. • LUSRF model was verified for different periods and areas. [ABSTRACT FROM AUTHOR]