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• Comparison of portable black carbon monitors with standard aethalometer AE33. • The effect of ambient environment and built-in algorithms were investigated. • Suggestion on application scenario of each micro monitor proposed. Black carbon (BC) is associated with adverse human health and climate change. Mapping BC spatial distribution imperatively requires low-cost and portable devices. Several portable BC monitors are commercially available, but their accuracy and reliability are not always satisfactory during continuous field observation. This study evaluated three models of portable black carbon monitors, C12, MA350 and DST, and investigates the factors that affect their performance. The monitors were tested in urban Beijing, where portable devices running for one month alongside a regular-size reference aethalometer AE33. The study considers several factors that could influence the monitors' performance, including ambient weather, aerosol composition, loading artifacts, and built-in algorithms. The results show that MA350 and DST present considerable discrepancies to the reference instrument, mainly occurring at lower concentrations (0–500 ng/m3) and higher concentrations (2500–8000 ng/m3), respectively. These discrepancies were likely caused by the anomalous noise of MA350 and the loading artifacts of DST. The study also suggests that the ambient environment has limited influence on the monitors' performance, but loading artifacts and accompanying compensation algorithms can result in unrealistic data. Based on the evaluation, the study suggests that C12 is the best choice for unsupervised field measurement, DST should be used in scenarios where frequent maintenance is available, and MA350 is suitable for research purposes with post-processing applicable. The study highlights the importance of assigning portable BC monitors to appropriate applications and the need for optimized real-time compensation algorithms. [Display omitted] [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols are important for absorbing aerosols, affecting global climate change and regional air quality, and potentially harming human health. From March to May 2023, we investigated black carbon aerosol levels and air pollution in Beijing. Employing methods such as linear regression, Potential Source Contribution Function (PSCF) and Concentration-Weighted Trajectory (CWT), we analyzed the characteristics and sources of black carbon aerosols in the region. Results indicate that the light absorption coefficients of BC and BrC decrease with increasing wavelength, with BrC accounting for less than 40% at 370 nm. Daily variations in BC and PM2.5 concentrations exhibit similar trends, peaking in March, and BC displays a distinct bimodal hourly concentration structure during this period. Aethalometer model results suggest that liquid fuel combustion contributes significantly to black carbon (1.08 ± 0.71 μg·m−3), surpassing the contribution from solid fuel combustion (0.31 ± 0.2 μg·m−3). Furthermore, the significant positive correlation between BC and CO suggests that BC emissions in Beijing predominantly result from liquid fuel combustion. Potential source area analysis indicates that air masses of spring in Beijing mainly originate from the northwest (40.93%), while potential source areas for BC are predominantly distributed in the Beijing–Tianjin–Hebei region, as well as parts of the Shandong, Shanxi and Henan provinces. Moreover, this study reveals that dust processes during spring in Beijing have a limited impact on black carbon concentrations. This study's findings support controlling pollution in Beijing and improving regional air quality. [ABSTRACT FROM AUTHOR]

Black carbon (BC) mass size distribution (BCMSD) is crucial in both the environment and the climate system due to BC's intense size-dependent absorption of solar radiation. BC-containing particles larger than 700 nm (BC >700) could contribute to more than half of bulk BC mass concentration. Unfortunately, previous methods concentrated on BC-containing particles of less than 700 nm because of technical limitations. The contribution of BC to absorption and the radiative effect might be underestimated without consideration of BC >700. In this study, equivalent BCMSD (eBCMSD) from 150 nm up to 1.5 µm was measured at high time resolution of 1 h for the first time by an aerodynamic aerosol classifier in tandem with an aethalometer in two field campaigns over eastern China, namely Changzhou located in the Yangtze River Delta and Beijing located in the North China Plain. The results revealed that the pattern of eBCMSD in Changzhou (Beijing) was mostly bimodal (unimodal) peaking at 240 and 1249 nm (427 nm). The peak diameter of eBCMSD in Changzhou did not shift significantly with increasing pollution (240 to 289 nm). In contrast, the peak diameter of eBCMSD in Beijing shifted towards larger sizes, from 347 to 527 nm, with increasing pollution, indicating that the aging process at the urban site was different from that at the regional background site. eBCMSD in both Changzhou and Beijing had a significant diurnal cycle with a smaller (larger) value of eBCMSD during daytime (nighttime). Equivalent BC >700 (eBC >700) was ubiquitous and varied significantly with different locations and pollution levels. The campaign-averaged contribution of eBC >700 to bulk eBC mass concentration (meBC,bulk), bulk absorption coefficient (σab,bulk) and estimated direct radiative forcing of eBC (DRF eBC) in Changzhou and Beijing were 27.8 % (20.9 %–36.5 %) and 24.1 % (17.5 %–34.2 %), 19.6 % (15.8 %–24.6 %) and 25.9 % (19.6 %–33.7 %) and 20.5 % (18.4 %–22.2 %) and 21.0 % (16.3 %–26.1 %), respectively. meBC,bulk , σab,bulk and DRF eBC of eBC >700 in Changzhou (Beijing) increased by a factor of 3.6 (5.1) from 0.11 (0.07) to 0.40 (0.36) µgm-3 , by a factor of 3.2 (5.5) from 0.54 (0.63) to 1.75 (3.45) Mm -1 and by a factor of 2.4 (4.7) from 0.1 (0.1) to 0.24 (0.47) W m -2 , respectively, with the aggravation of pollution. The contribution of eBC >700 to meBC,bulk and σab,bulk had a significant diurnal cycle with a higher (lower) fraction during daytime (nighttime) in both Changzhou and Beijing. A case study indicated that the contribution of eBC >700 to meBC,bulk , σab,bulk and DRF eBC could reach up to 50 %, 50 % and 40 %, respectively. It was highly recommended to consider the whole size range of BC-containing particles in model estimation of the BC radiative effect. [ABSTRACT FROM AUTHOR]

In 2013, several tombs were discovered and excavated in Southeastern Beijing, China, yielding various burial products. Among these were pottery towers, a representative artifact of the Han Dynasty rarely found in the area. Many studies on architectural aspects, such as construction type and construction situation, have been conducted based on the excavated pottery towers, but only a few have examined their raw materials or pigments. In this study, black, white, and red pigments were identified as carbon black, calcite, and cinnabar, respectively, through a multi-analysis approach. The manufacturing method of the pigment was established based on the crystal form and particle size of the pigment, by factoring in the pigment characteristics, which cannot be distinguished by component analysis and crystal structure analysis. We recommend that a continuous database be prepared and used in the future, not only for an interpretation of ancient pigments but also to identify the factors to be considered (physical characteristics, such as pigment particle size among others) when estimating the manufacturing process and conservation treatment. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols in the atmosphere play a significant role in climate systems due to their strong ability to absorb solar radiation. The lifetime of BC depends on atmospheric transport, aging and consequently on wet scavenging processes (in-cloud and below-cloud scavenging). In this study, sequential rainwater samples in eight rainfall events collected in 2 mm interval were measured by a tandem system including a single particle soot photometer (SP2) and a nebulizer. The results showed that the volume-weighted average (VWA) mass concentrations of refractory black carbon (rBC) in each rainfall event varied, ranging from 10.8 to 78.9 µg/L. The highest rBC concentrations in the rainwater samples typically occurred in the first fraction from individual rainfall events. The geometric mean median mass-equivalent diameter (MMD) decreased under precipitation, indicating that r BC with larger sizes was relatively aged and preferentially removed by wet scavenging. A positive correlation (R 2 = 0.73) between the VWA mass concentrations of r BC in rainwater and that in ambient air suggested the important contribution of scavenging process. Additionally, the contributions of in-cloud and below-cloud scavenging were distinguished and accounted for 74% and 26% to wet scavenging, respectively. The scavenging ratio of rBC particles was estimated to be 0.06 on average. This study provides helpful information for better understanding the mechanism of rBC wet scavenging and reducing the uncertainty of numerical simulations of the climate effects of rBC. [Display omitted] [ABSTRACT FROM AUTHOR]

Black carbon (BC), an important component of atmospheric aerosol, plays a significant role in regional climate, hydrological cycle, variation of monsoon rainfall, and human health. The 40-year detailed atmospheric BC over China from 1981 to 2020 is systematically investigated through the MERRA-2 reanalysis dataset. MERRA-2 BC generally showed a good correlation (R = 0.68) compared with 673 monthly samples from ground-based observation at 35 stations around China. The overall annual average of MERRA-2 BC concentration over China is 1.15 μg/m3, with a fast growth rate during 1981–2007 and a relatively slow decrease after that. The winter season has the highest mean concentration of BC, followed by autumn and spring, whereas summer shows relatively weaker values. The order of annual average BC concentrations during 1981–2020 is Beijing-Tianjin-Hebei region (BTH, 4.02 μg/m3) > Sichuan Basin (SB, 3.94 μg/m3) > Yangtze River Delta (YRD, 2.68 μg/m3) > Pearl River Delta (PRD, 1.47 μg/m3). The monthly mean BC concentrations over the BTH, YRD, PRD and SB are estimated to be smallest 3.18 μg/m3 in May, 1.94 μg/m3 in August, 0.82 μg/m3 in July, 3.04 μg/m3 in June, respectively, whilst largest consistently in December with 5.09 μg/m3, 3.83 μg/m3, 2.12 μg/m3, and 5.41 μg/m3, respectively. Our study indicates the primary potential source areas for BC are concentrated in the research city and its surroundings. Beijing and Chengdu are more BC-polluted areas than Shanghai and Guangzhou. Long-distance, regional transfer from south BTH contributes importantly to BC pollution in Beijing under the influence of prevailing southerly winds. The geographical location of Chengdu causes the transport and accumulation of BC inside the SB. [ABSTRACT FROM AUTHOR]

The light-absorbing organic aerosol (OA), known as brown carbon (BrC), has important radiative impacts; however, its sources and evolution after emission remain to be elucidated. In this study, the light absorption at multiple wavelengths, mass spectra of OA and microphysical properties of black carbon (BC) were characterized at a typical suburban environment in Beijing. The absorption of BC is constrained by its size distribution and mixing state, and the BrC absorption is obtained by subtracting the BC absorption from the total aerosol absorption. Aerosol absorption was further apportioned to BC, primary BrC and secondary BrC by applying the least correlation between secondary BrC and BC. The multilinear regression analysis on the factorized OA mass spectra indicated that the OA from traffic and biomass burning emission contributed to primary BrC. Importantly, the moderately oxygenated OA (O / C = 0.62) was revealed to highly correlate with secondary BrC. These OA had higher nitrogen content, in line with the nitrogen-containing functional groups detected by the Fourier transform infrared spectrometer. The photochemical processes were found to reduce the mass absorption cross section (MAC) of primary OA, reducing its contribution to total absorption by 20 %, at the same time increasing MAC for secondary OA, which showed a 30 % enhancement in contribution to total absorbance, implying the concurrent whitening and darkening of BrC. This provides field evidence that the photochemically produced secondary nitrogen-containing OA can considerably compensate for some bleaching effect on the primary BrC, hereby causing radiative impacts. [ABSTRACT FROM AUTHOR]

The vertical distribution of black carbon (BC), as well as its mixing state, is of great concern due to BC's strong regional climatic and environmental effects. In this study, vertical measurements were conducted through a moveable container based on a meteorological tower in the Beijing urban area during June and July. A total of 112 vertical profiles (0–240 m), including the concentrations of BC, O 3 , NO x and the optical properties of aerosols, were obtained. Based on BC concentration, the vertical profiles could be classified into four categories: uniform, gradual decrease, sharp decrease and sudden increase. The uniform type indicates strong vertical mixing with similar pollutant concentrations along the vertical direction. The gradual and sharp decrease types indicate stable vertical conditions with higher pollutant concentrations on the ground and lower concentrations at higher altitudes. Due to the strong radiation in summer, the vertical profiles exhibited a clear diurnal variation in which ∼ 80 % of profiles were uniform during the daytime and ∼ 40 %–90 % of profiles were of the gradual and sharp decrease types at night. O 3 is an exception, and its concentration generally increases with height, even under strong vertical mixing conditions. The size distribution of the BC core varied slightly along the vertical direction, and the coating thickness, denoted by the diameter ratio between the BC-containing particle and BC core (Dp/Dc), of BC increased with height under stable conditions. Although the coating thickness could increase the absorption ability with an average absorption enhancement of 1.25 at 23:00 LT (local time: UTC + 8), the vertical difference of Dp/Dc (2 %) was much lower than that of BC concentration (∼ 35 %). The vertical variation in absorption ability was mainly caused by the variation in BC concentration. In addition, O 3 and Dp/Dc occasionally increased during 06:00–08:00 but remained stable during 08:00–10:00. Vertical mixing and transportation from upper heights, such as the residual layer, could significantly influence the pollutant properties on the surface during early mornings. This study exhibits a continuous vertical picture of BC and its mixing state in urban areas, which would be helpful for understanding BC's regional environmental effect. [ABSTRACT FROM AUTHOR]

The effective density of black carbon (BC) is a crucial factor that is relevant to its aging degree and adds uncertainty in evaluating its climate effect. Here, we have developed a new method to retrieve the effective density of internally mixed BC in the atmosphere, combining field observations conducted from 15 November to 14 December 2016 in urban Beijing with the Köhler theory. The uncertainty in the retrieval method was evaluated to be within ±30 %, which was primarily caused by assumptions on both the hygroscopic parameter of organics and the proportional distribution of primary organic aerosols in different hygroscopic modes. Using the method, we find that the ambient internally mixed BC, accounting for 80 % ± 20 % of total BC aerosol particles, was retrieved with a campaign mean density of 1.1 ± 0.6 gcm-3 during the observed periods. The retrieved result was comparable with that reported in the literature. By applying a lower (0.14 gcm-3) and upper (2.1 gcm-3) limit of the retrieved BC density in the cloud condensation nuclei (CCN) number concentration (NCCN) estimation, we derived that the neglect of such variations in the BC density would lead to an uncertainty of - 28 %–11 % in predicting NCCN at supersaturations of 0.23 % and 0.40 %. We also find that the NCCN was more sensitive to the variations in BC density when it was <1.0 gcm-3. This illustrates the necessity of accounting for the effect of BC density on CCN activity closer to source regions where the BC particles are mostly freshly emitted. The CCN closure was achieved when introducing the retrieved real-time BC density and mixing state. This study provides a unique way of utilizing field measurements to infer ambient BC density and highlights the importance of applying variable BC density values in models when predicting CCN and assessing its relevant climate effect. [ABSTRACT FROM AUTHOR]

Unprecedented urbanization in China has led to serious urban heat island (UHI) issues, exerting intense heat stress on urban residents. Based on the observed temperature and PM 2.5 concentrations in Beijing over 2016–2020, we find diverse influences of aerosol pollution on urban heat island intensity (UHII) under different circulations. When northerly winds are prevalent in urban Beijing, UHII tends to be much higher in both daytime and nighttime and it is less affected by aerosol concentrations. However, when southerly and westerly winds are dominant in rural Beijing, UHII is significantly reduced by aerosol pollution. Using coupled aerosol-radiation weather simulations, we demonstrate the underlying physical mechanism which is associated with local circulation and resulting spatial distribution of aerosols. Our results also highlight the role of black carbon in aggravating UHI, especially during nighttime. It could thus be targeted for cooperative management of heat islands and aerosol pollution. [ABSTRACT FROM AUTHOR]

The radiative forcing of black carbon (BC) depends strongly on its mixing state in different chemical environments. Here we analyzed the chemical composition and mixing state of BC-containing particles by using a single-particle aerosol mass spectrometer and investigated their impact on light absorption enhancement (Eabs) at an urban (Beijing) and a rural site (Gucheng) in the North China Plain. While the BC was dominantly mixed with organic carbon (OC), nitrate, and sulfate at both the urban and rural sites, the rural site showed a much higher fraction of BC coated with OC and nitrate (36 % vs. 15 %–20 %). Moreover, the BC mixing state evolved significantly as a function of relative humidity (RH), with largely increased coatings of OC–nitrate and nitrate at high RH levels. By linking with an organic aerosol (OA) composition, we found that the OC coated on BC comprised dominantly secondary OA in Beijing, while primary and secondary OA were similarly important in Gucheng. Furthermore, Eabs was highly dependent on secondary inorganic aerosol coated on BC at both sites, while the coated primary OC also resulted in an Eabs of ∼ 1.2 for relatively fresh BC particles at the rural site. A positive matrix factorization analysis was performed to quantify the impact of different mixing states on Eabs. Our results showed a small Eabs (1.06–1.11) for BC particles from fresh primary emissions, while the Eabs increased significantly above 1.3 when BC was aged rapidly with increased coatings of OC–nitrate or nitrate; it can reach above 1.4 as sulfate was involved in BC aging. [ABSTRACT FROM AUTHOR]

The mass concentration of atmospheric particulate matter (PM) has been continuously decreasing in the Beijing-Tianjin-Hebei region. However, health endpoints do not exhibit a linear correlation with PM mass concentrations. Thus, it is urgent to clarify the prior toxicological components of PM to further improve air quality. In this study, we analyzed the long-term oxidative potential (OP) of water-soluble PM 2.5 , which is generally considered more effective in assessing hazardous exposure to PM in Beijing from 2018 to 2022 based on the dithiothreitol assay and identified the crucial drivers of the OP of PM 2.5 based on online monitoring of air pollutants, receptor model, and random forest (RF) model. Our results indicate that dust, traffic, and biomass combustion are the main sources of the OP of PM 2.5 in Beijing. The complex interactions of dust particles, black carbon, and gaseous pollutants (nitrogen dioxide and sulfur dioxide) are the main factors driving the OP evolution, in particular, leading to the abnormal rise of OP in Beijing in 2022. Our data shows that a higher OP is observed in winter and spring compared to summer and autumn. The diurnal variation of the OP is characterized by a declining trend from 0:00 to 14:00 and an increasing trend from 14:00 to 23:00. The spatial variation in OP of PM 2.5 was observed as the OP in Beijing is lower than that in Shijiazhuang, while it is higher than that in Zhenjiang and Haikou, which is primarily influenced by the distribution of black carbon. Our results are of significance in identifying the key drivers influencing the OP of PM 2.5 and provide new insights for advancing air quality improvement efforts with a focus on safeguarding human health in Beijing. [ABSTRACT FROM AUTHOR]

Vertical profiles of black carbon (BC) play a critical role in modifying the meteorological conditions such as temperature, planetary boundary layer height (PBLH), and regional circulation, which influence surface layer concentrations of PM 2.5 (particulate matter with a diameter of 2.5 µ m or less; the surface layer covers from 0 to 79.5 m). However, BC vertical profiles in current models usually have large uncertainties. In this study, by using measurements of BC vertical profiles in Beijing collected by King Air 350 aircraft and the Weather Research and Forecasting with Chemistry model (WRF-Chem) coupled with an improved integrated process (IPR) analysis scheme, we investigated the direct radiative effect (DRE) of BC with different vertical profiles on meteorology and PM 2.5 concentrations in Beijing during two severe haze events (11–12 and 16–19 December 2016). Compared with measurements in Beijing, the model overestimated BC concentrations by 87.4 % at the surface and underestimated BC mass by 14.9 % at altitudes of 300–900 m as averaged over the two pollution events. The BC DRE with the default vertical profiles from the model heated the air around 300 m altitude, but the warming would be stronger when BC vertical profiles were modified for each day using the observed data during the two severe haze events. Accordingly, compared to the simulation with the default vertical profiles of BC, PBLH was reduced further by 24.7 m (6.7 %) and 6.4 m (3.8 %) in Beijing in the first and second haze events, respectively, with the modified vertical profiles, and hence the surface layer PM 2.5 concentrations were higher by 9.3 µ g m -3 (4.1 %) and 5.5 µ g m -3 (3.0 %) over central Beijing, owing to increased positive contributions of vertical mixing and chemical processes. Furthermore, we quantified by sensitivity experiments the roles of BC vertical profiles with six exponential decline functions (C(h)=C0×e-h/hs and hs​​​​​​​ = 0.35, 0.48, 0.53, 0.79, 0.82, and 0.96) parameterized on the basis of the observations. A larger hs means less BC at the surface and more BC in the upper atmosphere, resulting in less solar radiation reaching the ground and consequently a stronger cooling at the surface (+ 0.21 with hs of 0.35 vs. - 0.13 ∘ with hs of 0.96). Our results indicate that it is very important to have accurate vertical profiles of BC in simulations of meteorology and PM 2.5 concentrations during haze events. [ABSTRACT FROM AUTHOR]

PM2.5 (fine) and PM2.5–10 (coarse) samples were collected using a Gent stack filter unit sampler in Xinzhen, Beijing. The 220 samples collected from September 2016 to June 2018 were analyzed by neutron activation analysis (NAA) and Black Carbon meter, and 19 elements were determined. Time series analysis, correlation analysis and enrichment factor analysis were performed on the determined component concentrations. The possible sources and temporal variation of some elements were discussed. In addition, the main pollution elements in the three different pollution events were obtained. Furthermore, the element component characteristics of the coarse and fine particles were determined. Finally, the source and backward trajectory of a heavy sandstorm were analyzed by HYSPLIT. Using neutron activation analysis (NAA) and Black Carbon meter, the concentrations of elements and Black Carbon (BC) were determined. Through the correlation analysis and time series analysis, the possible sources and temporal variation of some elements were discussed. Among them, Al, Ca, Ti and Mg in APM are contributed by soil and surface dust. They have strong correlation and similar temporal trend. The concentrations of these elements have obvious seasonal variations. The concentrations of these elements are high in spring and summer, and low in autumn and winter. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols play an important role in the radiation balance of the earth–atmosphere system. However, our knowledge of the long-term changes in equivalent black carbon (eBC) and aerosol optical properties in China is very limited. Here we analyze the 9-year measurements of eBC and aerosol optical properties from 2012 to 2020 in Beijing, China. Our results showed large reductions in eBC by 71 % from 6.25 ± 5.73 µ g m -3 in 2012 to 1.80 ± 1.54 µ g m -3 in 2020 and 47 % decreases in the light extinction coefficient (bext , λ = 630 nm) of fine particles due to the Clean Air Action Plan that was implemented in 2013. The seasonal and diurnal variations of eBC illustrated the most significant reductions in the fall and at nighttime, respectively. Δ eBC / Δ CO also showed an annual decrease from ∼ 7 to 4 ng m -3 ppbv -1 and presented strong seasonal variations with high values in spring and fall, indicating that primary emissions in Beijing have changed significantly. As a response to the Clean Air Action Plan, single-scattering albedo (SSA) showed a considerable increase from 0.79 ± 0.11 to 0.88 ± 0.06, and mass extinction efficiency (MEE) increased from 3.2 to 3.8 m 2 g -1. These results highlight the increasing importance of scattering aerosols in radiative forcing and a future challenge in visibility improvement due to enhanced MEE. Brown carbon (BrC) showed similar changes and seasonal variations to eBC during 2018–2020. However, we found a large increase of secondary BrC in the total BrC in most seasons, particularly in summer with the contribution up to 50 %, demonstrating an enhanced role of secondary formation in BrC in recent years. The long-term changes in eBC and BrC have also affected the radiative forcing effect. The direct radiative forcing (ΔFR) of BC decreased by 67 % from + 3.36 W m -2 in 2012 to + 1.09 W m -2 in 2020, and that of BrC decreased from + 0.30 to + 0.17 W m -2 during 2018–2020. Such changes might have important implications for affecting aerosol–boundary layer interactions and the improvement of future air quality. [ABSTRACT FROM AUTHOR]

Observations suggest that the vertical distributions of air pollutants, such as black carbon (BC), present as various types depending on the emission sources and meteorological diffusion conditions. However, the formation process and source appointment of some special BC profiles are not fully understood. In this paper, by using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) with a BC-tagging technique, we investigate the formation mechanism and regional sources of a BC peak in the free troposphere observed by an aircraft flight in Beijing (BJ) on 5 May 2018. The results show that the contribution rate of the Beijing–Tianjin–Hebei (BTH) region to the surface BC of BJ exceeded 80 % in this case. Local sources dominated BC in BJ from the surface to approximately 700 m (78.5 %), while the BC peak in the free troposphere (∼4000 m) was almost entirely imported from external sources (99.8 %). Combining BC tracking and process analysis, we find that horizontal advection (HADV) and vertical advection (VADV) processes played an important role in the convergent and upward movement and the transport of BC. The BC originating from the surface in central provinces, including Shanxi (SX), Henan (HN), and Hebei (HB), had been uplifted through a cyclone system 16 h previously, was transported to a height of approximately 3000 m above BJ, and was then lifted by the VADV process to approximately 4000 m. At the surface, BJ and its surroundings were under the control of a weak pressure gradient, leading to the accumulation of BC within the boundary layer. Our results indicate that cyclone systems can quickly lift air pollutants, such as BC, up to the free troposphere, as well as extend their lifetimes and further affect the regional atmospheric environment and climate. [ABSTRACT FROM AUTHOR]

Aerosols from surface emission can be transported upwards through convective mixing in the planetary boundary layer (PBL), which subsequently interact with clouds, serving as important sources to nucleate droplets or ice particles. However, the evolution of aerosol composition during this vertical transport has yet to be explicitly understood. In this study, simultaneous measurements of detailed aerosol compositions were conducted at two sites, namely urban Beijing (50 m above sea level – a.s.l.) and Haituo mountain (1344 m a.s.l.) during wintertime, representing the anthropogenically polluted surface environment and the top of the PBL, respectively. The pollutants from surface emissions were observed to reach the mountain site on daily basis through daytime PBL convective mixing. From the surface to the top of PBL, we found efficient transport or formation of lower-volatility species (black carbon, sulfate, and low-volatile organic aerosol, OA); however, a notable reduction in semivolatile substances, such as the fractions of nitrate and semivolatile OA reduced by 74 % and 76 %, respectively, during the upward transport. This implies that the mass loss of these semivolatile species was driven by the evaporation process, which repartitioned the condensed semivolatile substances to the gas phase when aerosols were transported and exposed to a cleaner environment. In combination with the oxidation processes, these led to an enhanced oxidation state of OA at the top of the PBL compared to surface environment, with an increase of oxygen to carbon atomic ratio by 0.2. Such a reduction in aerosol volatility during vertical transport may be important in modifying its viscosity, nucleation activity, and atmospheric lifetime. [ABSTRACT FROM AUTHOR]

The complex particle morphology of black carbon (BC) induces considerable uncertainties in constraining its optical properties. In particular, the diversity of how the BC core and coating are combined is yet to be resolved due to the lack of direct ambient quantification. In this study, by concurrent measurements of the electrical mobility diameter (Dm) and optical volume‐equivalent diameter (Dve), the dynamic shape factor (χ = Dm/Dve) of ambient BC‐containing particles at different mixing states was quantified for the first time. BC in urban Beijing showed a widely distributed χ of 1.4 ± 0.43. Particles with larger refractory BC (rBC) cores showed higher non‐sphericity and higher χ. A ten‐fold increase in the volume ratio of the coating over rBC (VR) could decrease the fraction of fractal BC by 36%. This study proposed a χ‐VR space to describe the particle shape, which is able to include all ambient quantified BC morphologies in optical model. Plain Language Summary: Black carbon (BC) is an important short‐lived light‐absorbing aerosol component in the atmosphere. Its optical properties are complicated by the complex particle morphology, such as the non‐BC substances associated with it and the combination of BC and non‐BC substances within particle. The previous quantification of particle morphology could not distinguish the information specifically for ambient BC, nor the single BC particle characterization can represent full diversities for all particles. This study used concurrent measurements of volume‐equivalent and mobility diameter of BC‐containing particles (BCc) to characterize the coating content and particle shape online for all BC particles in the ambient environment. As a result, we can include all the measured particle morphology information in optical models. Particles with larger BC cores showed higher non‐sphericity, with a greater discrepancy between the measured absorbing properties and that calculated by the Mie theory. Key Points: The morphology of ambient black carbon‐containing particles was characterized by volume‐equivalent and mobility diameter measurementsBlack carbon with higher coatings showed more spherical shapesA space using coatings and particle shape was developed to incorporate morphology information for all black carbon‐containing particles [ABSTRACT FROM AUTHOR]

Under the influence of Coronavirus Disease 2019 (COVID-19), China conducted a nationwide lockdown (LD) which significantly reduced anthropogenic emissions. To analyze the different impacts of COVID-19 on black carbon (BC) in the two representative regions in China, one-year continuous online measurements of BC were conducted simultaneously in Beijing and Tibet. The average concentration in the LD period was 20% higher than that in the pre-LD period in Beijing, which could be attributed to the increase of transport from southwestern neighboring areas and enhanced aged BC. In contrast to megacity, the average concentration of BC in Tibet decreased over 70% in the LD period, suggesting high sensitivity of plateau background areas to the anthropogenic emission reduction in South Asia. Our study clearly showed that BC responded very differently in megacity and background areas to the change of anthropogenic emission under the lockdown intervention. Plain Language Summary China has been influenced by Coronavirus Disease 2019 (COVID-19) in 2020 and the nationwide lockdown (LD) caused emission reduction from human activities. As an important component of PM2.5, black carbon (BC) can absorb light and effect the climate. It is essential to analyze the different impacts of COVID-19 on BC in the two representative regions in China. In this study, BC was measured simultaneously in Beijing and Tibet. The average concentration in the LD was 20% higher than that in the pre-LD period in Beijing, which could be attributed to the increase of transport from southwestern neighboring areas and enhanced aged BC. In contrast to megacity, the average concentration of BC in Tibet decreased over 70% in the LD period, which was mainly the result of the anthropogenic emission reduction in South Asia. Our study clearly showed that BC responded very differently in megacity and background areas to the change of anthropogenic emission, which could help to form better and more specific control strategies for BC under representative atmospheric environment in China. [ABSTRACT FROM AUTHOR]

Considering human activities are the most direct and important factors leading to the accumulation and loss of soil black carbon (BC), a detailed understanding of soil BC in different functional zones and reasonable soil management are the keys to determine whether soil is the carbon source or carbon sink. In this study, carbon concentrations and isotope compositions of black carbon (BC%, δ13CBC) and organic carbon (OC, δ13COC) were determined in topsoil from different functional zones (roadside grass verges, parks, residential areas, mines, arable lands, woodlands and wastelands) in urban and suburban of Beijing, China. The organic carbon (OC) content in soils of the urban area (averaging 1.67%) is higher than in suburban areas (averaging 1.05%). Black carbon is not evenly distributed across different functional zones, but is more concentrated and variable in urban areas (0.11–2.43%, averaging 0.73%) than in suburban areas (0.03–0.70%, averaging 0.18%). The ratios of BC% to OC% in suburban areas (0.04–0.40) are smaller than in urban areas (0.15–0.98). The δ13CBC of topsoil (–26.35...–20.85‰) reflects that coal combustion has a strong impact on soil BC accumulation in Beijing. The carbon isotope differences between OC and BC of the suburban and urban topsoils are positive (averaging +0.56‰) and negative (averaging –0.41‰), respectively. This suggests that urban areas are seriously influenced by human activities which lead to a large amount of fossil fuel combustion, but suburban areas have received a uniform deposition of atmospherically transported finer BC aerosols. [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) forms an important component of particulate matter globally, due to its impact on climate, the environment and human health. Identifying and quantifying its emission sources are critical for effective policymaking and achieving the desired reduction in air pollution. In this study, we present the first direct measurements of urban BC fluxes using eddy covariance. The measurements were made over Beijing within the UK-China Air Pollution and Human Health (APHH) winter 2016 and summer 2017 campaigns. In both seasons, the mean measured BC mass (winter: 5.49 ng m -2 s -1 , summer: 6.10 ng m -2 s -1) and number fluxes (winter: 261.25 particles cm -2 s -1 , summer: 334.37 particles cm -2 s -1) were similar. Traffic was determined to be the dominant source of the BC fluxes measured during both seasons. The total BC emissions within the 2013 Multi-resolution Emission Inventory for China (MEIC) are on average too high compared to measured fluxes by a factor of 58.8 (winter) and 47.2 (summer). Only a comparison with the MEIC transport sector shows that emissions are also larger (factor of 37.5 in winter and 37.7 in summer) than the measured flux. Emission ratios of BC / NO x and BC / CO are comparable to vehicular emission control standards implemented in January 2017 for gasoline (China 5) and diesel (China V) engines, indicating a reduction of BC emissions within central Beijing, and extending this to a larger area would further reduce total BC concentrations. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is a major light-absorbing component in the atmosphere and plays an important role in aerosol radiative forcing. In this study, the combination of monitoring data and the WRF-Chem model was used to study the source apportionment of BC in China during January 2017. Meanwhile, the aerosol-radiation interaction (ARI) effect of BC was also simulated. We found that the average BC/PM2.5 ratios were 4.8%, 4.2%, and 3.8% in Shijiazhuang, Tangshan, and Beijing, respectively. The source apportionment suggested that traffic emissions played a dominant role in the BC concentration over Beijing. The traffic, residential, industrial, and power contributions accounted for 41%, 32%, 25%, and 2% of total concentration, respectively. The BC concentration in Beijing was also affected by regional transport. During January, the contributions of monthly regional transport to BC and PM2.5 concentrations in Beijing were 41% and 49%, respectively. BC emissions decreased downward shortwave radiation (SWDOWN) at the surface, leading to a decrease in temperature. As a result, the planetary boundary layer height (PBLH) development was suppressed and the relative humidity increased. The stable meteorological conditions suppressed the dispersion of air pollutants and increased BC concentrations. Traffic emissions decreased the monthly SWDOWN by approximately 2.2 W/m2, decreased 2 m temperature (T2) by approximately 0.1 °C, increased 2 m relative humidity (RH2) by approximately 0.5%, and decreased PBLH by approximately 4.4 m. [ABSTRACT FROM AUTHOR]

Black carbon aerosols play an important role in climate change because they directly absorb solar radiation. In this study, the mixing state of refractory black carbon (rBC) at an urban site in Beijing in the early summer of 2018 was studied with a single-particle soot photometer (SP2) as well as a tandem observation system with a centrifugal particle mass analyzer (CPMA) and a differential mobility analyzer (DMA). The results demonstrated that the mass-equivalent size distribution of rBC exhibited an approximately lognormal distribution with a mass median diameter (MMD) of 171 nm. When the site experienced prevailing southerly winds, the MMD of rBC increased notably, by 19 %. During the observational period, the ratio of the diameter of rBC-containing particles (Dp) to the rBC core (Dc) was 1.20 on average for Dc=180 nm, indicating that the majority of rBC particles were thinly coated. The Dp/Dc value exhibited a clear diurnal pattern, with a maximum at 14:00 LST and a Dp growth rate of 2.3 nm h -1 ; higher Ox conditions increased the coating growth rate. The microphysical properties of rBC were also studied. Bare rBC particles were mostly found in fractal structures with a mass fractal dimensions (Dfm) of 2.35, with limited variation during both clean and polluted periods. The morphology of rBC changed with coating thickness increasing. When the mass ratio of nonrefractory matter to rBC (MR) was <1.5, rBC-containing particles were primarily found in external fractal structures, and they changed to a core–shell structure when MR>6 , at which point the measured scattering cross section of rBC-containing particles was consistent with that based on the Mie-scattering simulation. We found that only 28 % of the rBC-containing particles were in core–shell structures with a particle mass of 10 fg in the clean period but that proportion increased considerably, to 45 %, in the polluted period. Due to the morphology change, the absorption enhancement (Eabs) was 12 % lower than that predicted for core–shell structures. [ABSTRACT FROM AUTHOR]

Refractory black carbon (rBC) in the atmosphere is known for its significant impacts on climate. The relationship between the microphysical and optical properties of rBC remains poorly understood and is influenced by its size and mixing state. Mixing state also influences its cloud scavenging potential and thus atmospheric lifetime. This study presents a coupling of a centrifugal particle mass analyser (CPMA) and a single-particle soot photometer (SP2) for the morphology-independent quantification of the mixing state of rBC-containing particles, used in the urban site of Beijing as part of the Air Pollution and Human Health–Beijing (APHH-Beijing) project during winter (10 November–10 December 2016) and summer (18 May–25 June 2017). This represents a highly dynamic polluted environment with a wide variety of conditions that could be considered representative of megacity area sources in Asia. An inversion method (used for the first time on atmospheric aerosols) is applied to the measurements to present two-variable distributions of both rBC mass and total mass of rBC-containing particles and calculate the mass-resolved mixing state of rBC-containing particles, using previously published metrics. The mass ratio between non-rBC material and rBC material (MR) is calculated to determine the thickness of a hypothetical coating if the rBC and other material followed a concentric sphere model (the equivalent coating thickness). The bulk MR (MR bulk) was found to vary between 2 and 12 in winter and between 2 and 3 in summer. This mass-resolved mixing state is used to derive the mass-weighted mixing state index for the rBC-containing particles (χrBC). χrBC quantifies how uniformly the non-rBC material is distributed across the rBC-containing-particle population, with 100 % representing uniform mixing. The χrBC in Beijing varied between 55 % and 70 % in winter depending on the dominant air masses, and χrBC was highly correlated with increased MR bulk and PM 1 mass concentration in winter, whereas χrBC in summer varied significantly (ranging 60 %–75 %) within the narrowly distributed MR bulk and was found to be independent of air mass sources. In some model treatments, it is assumed that more atmospheric ageing causes the BC to tend towards a more homogeneous mixture, but this leads to the conclusion that the MR bulk may only act as a predictor of χrBC in winter. The particle morphology-independent and mass-based information on BC mixing used in this and future studies can be applied to mixing-state-aware models investigating atmospheric rBC ageing. [ABSTRACT FROM AUTHOR]

The effective density (ρeff) of refractory black carbon (rBC) is a key parameter relevant to its mixing state that imposes great uncertainty in evaluating the direct radiation forcing effect. In this study, a tandem differential mobility analyzer–centrifugal particle analyzer–single-particle soot photometer (DMA–CPMA–SP2) system was used to investigate the relationship between the effective density (ρeff) and the mixing state of rBC particles during the winter of 2018 in the Beijing megacity. During the experiment, aerosols with a known mobility diameter (Dmob) and known ρeff values (0.8, 1.0, 1.2, 1.4, 1.6, and 1.8 g cm -3) were precisely selected and measured by the SP2 to obtain their corresponding mixing states. The results showed that the ρeff well represented the morphological variation in rBC-containing particles. The rBC-containing particles changed from an irregular structure to a compact spherical structure with the increase in ρeff. A ρeff value of 1.4 g cm -3 was the morphological transition point. The morphology and ρeff value of the rBC-containing particles were intrinsically related to the mass ratio of non-refractory matter to rBC (MR). As the ρeff values of the rBC-containing particles increased from 0.8 to 1.8 g cm -3 , the MR of the rBC-containing particles significantly increased from 2 up to 6–8, indicating that atmospheric aging processes were likely to lead to the reconstruction of more compact and regular particle shapes. During the observation period, the ρeff of the majority of rBC-containing particles was smaller than the morphology transition point independent of the pollution conditions. This suggested that the major rBC-containing particles did not have a spherical structure. Simulation based on an aggregate model considering the morphological information of the particles demonstrated that absorption enhancement of rBC-containing particles could be overestimated by ∼ 17 % by using a core–shell model. This study highlights the strong dependence of the morphology of ambient rBC-containing particles on ρeff and will be helpful for elucidating the microphysical characteristics of rBC and reducing uncertainty in the evaluation of rBC climate effects and health risks. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is one of the most important climate pollutants due to its strong positive radiative forcing on the climate system. However, long-term observation of BC is inadequate, and its trend remains unknown at both regional and global scales. In this study, using quality-controlled ground-based black carbon observations at 34 stations, the climatology of BC mass concentration during 2006–2017 in China was evaluated for the first time. The national annual average BC concentration was 3534 ng/m3, and the concentration exhibited large spatial variation, from a minimum of 272 ng/m3 to a maximum of 10,228 ng/m3. Significant seasonal variations were also observed. The peak BC concentration (4763 ± 3380 ng/m3) occurred during winter, followed by autumn (3752 ± 2623 ng/m3) and spring (3022 ± 2121 ng/m3). The lowest BC concentration occurred in summer (2583 ± 1780 ng/m3) due to decreased emissions, wet removal by precipitation, and diffusion induced by strong turbulent mixing. Additionally, the diurnal variability at about 80% of the stations in China showed a bimodal pattern. Daily maximum BC concentration during 0000–0600, 0600–1200, 1200–1800, and 1800–2400 local solar time accounted for 0, 41, 12, and 47% of the total, respectively. In particular, the diurnal and monthly variations in BC were explicitly analyzed at seven baseline stations. Surface BC has exhibited a significant declining trend across China, which is partly corroborated by the increase in single scattering albedo during the same period in Beijing. Also, the BC radiative forcing at the top of the atmosphere has declined at the rate of − 0.9 ± 0.1 W/m2/10 years over China, which differs from with the trend in the simulation using the CMIP6 emission. The decreasing BC has led to a larger reduction rate in atmospheric heating (− 3.7 ± 0.4 W/m2/10 years), implying a less stable atmosphere that facilitates the dispersion of air pollutants. The declining BC burden implies for both the air quality in China and regional climate change. [ABSTRACT FROM AUTHOR]

The light absorption enhancement (E abs) of black carbon (BC) caused by non-BC materials is an important source of uncertainty in radiative forcing estimate, yet remains poorly understood in relatively polluted environment such as the megacity Beijing. Here BC absorption enhancement at 630 nm was in-situ measured using a thermodenuder coupled with a soot particle aerosol mass spectrometer and a single scattering albedo monitor in Beijing in summer. The project average (±1σ) E abs was 1.59 (±0.26), suggesting a significant amplification of BC absorption due to coating materials. E abs presented a clear daytime increase due to enhanced photochemical processing, and a strong dependence on the mass ratios of non-BC coatings to BC (R BC). Our results showed that the increase in E abs as a function of R BC was mainly caused by the increased contributions of secondary aerosol. Further analysis showed that the BC absorption enhancement in summer in Beijing was mainly associated with secondary formation of nitrate, sulfate and highly oxidized secondary organic aerosol (SOA), while the formation of freshly and less oxidized SOA appeared not to play an important role. Image 1 • A significant BC absorption enhancement (∼1.6) in summer in Beijing. • Light absorption enhancement depends strongly on the amount of BC coatings. • SIA and highly oxidized SOA play the most impacts on absorption enhancement. [ABSTRACT FROM AUTHOR]

The physical properties of black carbon (BC) including the mass loading, size distribution and mixing state were in-situ characterized by aircraft measurements using a single particle soot photometer (SP2) in the lower troposphere over Beijing area. The flights were conducted in both late spring and winter during the daytime with well-developed planetary boundary layer (PBL). The BC mass in the PBL (BC PBL) in late spring showed no apparent vertical gradient nor correlation with the PBL height (PBLH) due to strong convective mixing; in winter the BC PBL was more concentrated near ground and anti-correlated with the PBLH due to dilution effect of the dominant cleaner northerly air masses at higher altitude. The BC mass loading at height h , C(h) within the PBL can be extended from the surface level (C0) in late spring; for levels above the PBL, C(h) can be parameterized by applying an exponential decline function C(h) = C0*exp(h/hs) , with the scale height (hs) of 0.31 ± 0.16 km and 0.66 ± 0.24 km for late spring and winter respectively. This parameterization excluded the profiles for: turbulent conditions when the BC mass was efficiently vented upwards and diluted, expressed as C(h) = C0 up to the top of the PBL; or in periods of strong southerly advection, when the entire column was significantly influenced by regional transport from the polluted south regions. The BC core mass median diameters (MMD) were commonly populated at 205–220 nm in both seasons, with additional mode of MMD ∼195 nm also frequently observed in late spring. The bulk relative coating thickness of BC (coated diameter divided by uncoated core diameter D p /D c) in the PBL mostly populated at 2.0–2.2 but at ∼1.2–1.6 in the lower free troposphere (FT). The mass absorption cross section of BC at 550 nm (MAC550), constrained by the SP2 measurements, was largely influenced by the coating thickness, was relatively consistent in the PBL at ∼8.6 m2 g−1, but reduced to 7–7.5 m2 g−1 in the FT or turbulent condition due to decreased coatings. The BC was found to exhibit smaller particle size in the FT but larger in the PBL, which may imply larger BC have been scavenged by low-level clouds. The BC particles trapped in the PBL or regionally transported from polluted region represent the most absorbing element in the particulate matter population and should be particularly considered in evaluating the radiative forcing impact of aerosols over this region. • Vertical profiles of black carbon physical properties in the lower troposphere were in-situ characterized over Beijing. • Black carbon at different layers was influenced by seasonal emission and meteorological conditions. • These results will improve modelling on black carbon radiative forcing and constrain remote sensing absorption measurement. [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]

The morphology and effective density of externally mixed black carbon (extBC) aerosols, important factors affecting the radiative forcing of black carbon, were studied using a tandem technique coupling a differential mobility analyzer (DMA) with a single-particle soot photometer (SP2). The study extended the mass–mobility relationship to large extBC particles with a mobility diameter (dmob) larger than 350 nm, a size range seldom included in previous tandem measurements of BC aggregates in the atmosphere. The experiment was conducted at an urban site in Beijing during a 19 d winter period from 23 January to 10 February 2018. Ambient dry particles were selected by the DMA, and the size-resolved extBC particles were distinguished from particles with a thick coating (internally mixed) according to the time delay between the incandescence signal peak and the scattering peak detected by the SP2. The masses of the extBC particles were then quantified. The time differences between the DMA size selection and the SP2 measurement were processed previously. The normalized number size distributions were investigated at the prescribed dmob sizes in the range of 140–750 nm to provide the typical mass of extBC at each dmob. On this basis, the mass–mobility relationship of the ambient extBC was established, inferring a mass–mobility scaling exponent (Dfm) (an important quantity for characterizing the morphology of fractal-like BC aggregates) with a value of 2.34±0.03 in the mobility range investigated in this study. This value is comparable with those of diesel exhaust particles, implying a predominant contribution of vehicle emissions to the ambient extBC in urban Beijing. Compared to the clean period, a higher Dfm value was observed in the polluted episode, indicating a more compact BC aggregate structure than that in the clean period. The effective densities (ρeff) of the extBC in the same dmob range were also derived, with values gradually decreasing from 0.46 g cm -3 at 140 nm mobility to 0.14 g cm -3 at 750 nm mobility. The ρeff values were slightly lower than those measured using the DMA–aerosol particle mass analyzer (APM) system. The difference in ρeff values was likely due to the lower BC masses determined by the SP2 compared to those measured by the APM at the same mobility, since the SP2 measured the refractory BC (rBC) mass instead of the total mass of the BC aggregate, which consists of both rBC and a possible fraction of nonrefractory components measured by the APM. The ρeff values in the 280–350 nm dmob range were much closer to the values for soot aggregates reported in the literature. It might be related to the more compact structure of BC aggregates in this range, resulting from the reconstruction effect by volatile and/or semivolatile components in the atmosphere. The reconstruction effect might also result in a hiatus in the increased dynamic shape factor in the range of 200–350 nm, which presented an overall increase from 2.16 to 2.93 in the 140–750 nm dmob range. [ABSTRACT FROM AUTHOR]

The effect of black carbon (BC) on air quality and the climate is still unclear, which is partly because of the poor understanding regarding the BC aging process in the atmosphere. In this work, we developed a new approach to simulate the BC mixing state (i.e., other species coated on the BC surface) based on an emissions inventory and back-trajectory analysis. The model tracks the evolution of the BC aging degree (characterized by the size ratio of the whole particle and BC core) during atmospheric transport. Using the models, we quantified the mass-averaged aging degree of total BC particles transported to a receptor (e.g., an observation site) from various emission origins (i.e., 0.25∘×0.25∘ grids). The simulations showed good agreement with the field measurements, which validated our model calculation. Modeling the aging process of BC during atmospheric transport showed that it was strongly dependent on emission levels. BC particles from extensive emission origins (i.e., polluted regions) were characterized by a higher aging degree during atmospheric transport due to more co-emitted coating precursors. On the other hand, high-emission regions also controlled the aging process of BC particles that were emitted from cleaner regions and passed through these polluted regions during atmospheric transport. The simulations identified the important roles of extensive emission regions in the BC aging process during atmospheric transport, implying the enhanced contributions of extensive emission regions to BC light absorption. This provides a new perspective on the phenomenon of pollution building up in the North China Plain, further demonstrating that this is mainly driven by regional transport and transformation. The simulation of the BC aging degree during atmospheric transport provided more clues for improving air pollution and climate change. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is known to have major impacts on both human health and climate. The populated megacity represents the most complex anthropogenic BC emissions where the sources and related impacts are very uncertain. This study provides source attribution and characterization of BC in the Beijing urban environment during the joint UK–China APHH (Air Pollution and Human Health) project, in both winter (November–December 2016) and summer (May–June 2017). The size-resolved mixing state of BC-containing particles was characterized by a single-particle soot photometer (SP2) and their mass spectra was measured by a soot particle aerosol mass spectrometer (SP-AMS). The refractory BC (rBC) mass loading was around a factor of 2 higher in winter relative to summer, and more variable coatings were present, likely as a result of additional surface emissions from the residential sector and favourable condensation in the cold season. The characteristics of the BC were relatively independent of air mass direction in summer, whereas in winter air masses from the Northern Plateau were considerably cleaner and contained less-coated and smaller BC, but the BC from the Southern Plateau had the largest core size and coatings. We compare two online source apportionment methods using simultaneous measurements made by the SP2, which measures physical properties of BC, and the chemical approach using the positive matrix factorization (PMF) of mass spectra from the SP-AMS for the first time. A method is proposed to isolate the BC from the transportation sector using a mode of small BC particles (core diameter Dc<0.18 µ m and coating thickness ct < 50 nm). This mode of BC highly correlated with NOx concentration in both seasons (∼14 ng m -3 BC ppb -1 NOx) and corresponded with the morning traffic rush hour, contributing about 30 % and 40 % of the total rBC mass (35 % and 55 % in number) in winter and summer respectively. The BC from coal burning or biomass burning was characterized by moderate coatings (ct = 50–200 nm) contributing ∼20 %–25 % of rBC mass. Large uncoated BC particles (Dc>0.18 µ m and ct < 50 nm) were more likely to be contributed by coal combustion, as these particles were not present in urban London. This mode was present in Beijing in both winter (∼30 %–40 % rBC mass) and summer (∼40 % rBC mass) but may be dominated by the residential and industrial sector respectively. The contribution of BC thickly coated with secondary species (ct > 200 nm) to the total rBC mass increased with pollution level in winter but was minor in summer. These large BC particles importantly enhanced the absorption efficiency at high pollution levels – in winter when PM 1 > 100 µ g m -3 or BC > 2 µ g m -3 , the absorption efficiency of BC increased by 25 %–70 %. The reduction of emissions of these large BC particles and the precursors of the associated secondary coating will be an effective way of mitigating the heating effect of BC in urban environments. [ABSTRACT FROM AUTHOR]

Highlights • Roadside vehicular pollution is simulated by coupling traffic dynamics, emission model and pollutant dispersion model. • Non-local trucks greatly increase traffic emissions and roadside concentration of BC at night. • Unfavourable dispersion conditions are a major reason for higher roadside BC concentration at night. • Smart transportation management should consider the temporal traffic and meteorological patterns. Abstract Increasing attentions have been attained to transportation air quality in developing countries. Multi-disciplinary models are useful to understand the relationship between traffic dynamics and air quality, however, which generate higher demand for input data regarding traffic and emission. In Beijing, the environmental impact from non-local heavy-duty trucks (HDTs) has not been evaluated yet, which may be an important reason for higher black carbon concentration at night. This study selected one link of the North Fourth Ring Road, a major urban traffic corridor, to characterize BC pollution for typical weekdays by coupling traffic data investigation, vehicle emission calculation and roadside concentration modelling. We found local meteorological conditions would play a more governing role than changes of vehicle emissions in elevating roadside BC concentration, in particular for the night hours when dispersion conditions were significantly worsened. AERMOD-modelled results were in a good agreement with simultaneously observed BC concentration data, which could be responsible for 17% of the total roadside BC concentration during the summer period. We further identified that approximately 30–40% of the total HDT fleet on the North Fourth Ring Road were non-local HDTs, which could increase total BC emissions by ∼60% and roadside BC concentration by ∼2 μg m−3 at night compared to a local HDTs exclusive scenario. In addition to stricter emission controls for non-local HDTs, policy-makers may consider allowing HDTs to drive within the urban area at noon under a delicate scheme based on fine-grained weather forecasting. [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]

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]

Due to the lack of black carbon (BC) measurement data in some cases, elemental carbon (EC) is often used as a surrogate of BC, with a simple assumption that they are interchangeable. Such assumption will inevitably lead to uncertainties in radiative forcing estimation and health impact assessment. In order to quantitatively and systematically evaluate the relationship between BC and EC as well as factors responsible for their difference, 3-year collocated equivalent BC (eBC) and EC measurements with 1-h resolution were performed in Beijing, China continuously from 2016 to 2019. EBC concentration was measured by the multi-wavelength aethalometer (AE-33) based on optical analysis, while EC concentration was determined by semi-continuous OC/EC analyzer with thermal-optical method. The results showed that around 90% of eBC concentration was higher than that of EC, with average difference between eBC and EC as 1.21 μg m−3 (accounting for 33% of average eBC in Beijing). EBC and EC concentrations exhibited strong correlation (r = 0.90) during the whole study period, but the slopes (or eBC/EC ratio) and correlation coefficients varied across seasons (spring: 1.67 and 0.94; summer: 0.91 and 0.65; fall: 1.15 and 0.88; winter: 1.09 and 0.91, respectively). Based on the information from shell/core ratios by Single Particle Soot Photometer (SP2), source apportionment results by positive matrix factorization model, and chemical composition of PM 2.5 , the differences between eBC and EC concentrations were found to be primarily related to BC aging process and secondary components as evidenced by strong positive correlation with secondary species (e.g., secondary organic carbon and nitrate). This study provided seasonal specific conversion factors of eBC and EC in Beijing and helpful reference for other areas, which will contribute new knowledge of carbonaceous aerosol and reduce uncertainty in assessing future climate change and health studies of BC. • About 90% of eBC mass were higher than EC in Beijing based on 3-year measurement. •EBC and EC were strongly correlated whereas eBC/EC ratios varied with season. •The difference between eBC and EC was related to BC aging and secondary species. [ABSTRACT FROM AUTHOR]

Abstract: The spatial and temporal distribution and the flux of black carbon (BC) concentration in Beijing were continuously investigated over a two-year period at five sites to highlight the relative influence of contributing sources. The results demonstrate firstly that there is significant spatio-temporal variability of BC in Beijing. Highest concentrations occurred during winter primarily due to stagnant meteorological conditions, and seasonal BC sources, such as coal combustion for heating purposes. Biomass burning was identified as a minor seasonal source during the summer months. BC also varied spatially with higher concentrations in the SE of Beijing and lower concentrations in the NW, due to the differing emission intensity of various local BC sources such as traffic and industry. Frequently, overnight BC concentrations were higher due to specific meteorological conditions, such as the lower urban mixing layer height and various anthropogenic activities, such as exclusive night-time heavy duty vehicle traffic in the inner-city. [Copyright &y& Elsevier]

Abstract: Black carbon (BC), carbon monoxide (CO), and particle number size distribution were measured near a major urban expressway of Beijing during summer and winter field campaigns in 2009. BC was also observed at urban and rural sites. The temporal variations of BC and its relationships with CO and particle number size distribution were analyzed. The average BC concentrations at the roadside site were 12.3 and 17.9 μg m−3 during the summer and winter campaigns, respectively. BC concentrations ranked in the order of roadside > urban > rural. A general diurnal pattern at all sites showed that the higher BC levels were observed at night. The diurnal pattern of summertime BC at the roadside site followed the variations of heavy-duty diesel vehicles (HDDVs). The increased proportion of HDDVs at night contributed to high ΔBC/ΔCO ratios. This study suggests that HDDVs are an important contributor to nighttime BC and particle number concentrations of both Aitken and accumulation modes near major roadways in Beijing, especially in summer. [Copyright &y& Elsevier]

Abstract: Atmospheric particles were studied before, during, and after the period of the Olympic Summer Games in Beijing, China, in August 2008 in order to investigate the efficiency of the mitigation measures implemented by the Chinese Government. Total suspended particles (TSP) and fine particles (PM2.5 and PM1) were collected continuously from October 2007 to February 2009 and were analyzed in detail with regard to mass and element concentrations, water-soluble ions, and black carbon (BC). Mass as well as element concentrations during the Olympic air quality control period were lower than the respective concentrations during the time directly before and after the Olympic Games. The results showed that the applied aerosol source control measures, such as shutting down industries and reducing traffic, had a huge impact on the reduction of aerosol pollution in Beijing. However, the meteorological conditions, especially rainfall, certainly also contributed to the successful reduction of particulate air pollution. Coarse particles were reduced more efficiently than finer particles, which indicates that long-range transport of atmospheric particles is difficult to control and that presumably the established mitigation area was not large enough. The study further showed that elements from predominantly anthropogenic sources, such as S, Cu, As, Cd, and Pb, as well as BC, were reduced more efficiently during the Olympic Games than elements for which geogenic sources are more significant, such as Al, Fe, Rb or Sr. Furthermore, the mentioned anthropogenic element concentrations were reduced more in the finer PM2.5 samples whereas geogenic ones were reduced stronger in TSP samples including the coarser fraction. Consequently, it can be assumed that the mitigation measures, as intended, were successful in reducing more toxic and health-relevant particles from anthropogenic sources. Firework displays, especially at the Opening Ceremony, could be identified as a special short-time source for atmospheric particles during the Olympic Games. [Copyright &y& Elsevier]

Abstract: Nitrogen oxides (NO x ) and black carbon (BC) emission factors (EF) of 440 on-road diesel trucks were determined by conducting on-road chasing studies in Beijing and Chongqing, China, in the winter 2010. NO x and BC EF distributions are reported. The median NO x EFs for trucks sampled on level roads in Chongqing and Beijing are 40.0 and 47.4g kg-fuel−1, respectively. The median BC EFs are 1.1 and 0.4g kg-fuel−1in Chongqing and Beijing, respectively. In addition, a clear downward trend of BC EFs of on-road diesel trucks sampled in Beijing since 2008 is observed. Moreover, Beijing-registered trucks had the lowest BC EFs among the entire sample. These observations appear to reflect the effectiveness of emission standard and fuel quality standard implemented in Beijing (China IV) and nationwide (China III) in reducing BC (and likely overall particulate matter) emission. However, NO x EFs for Beijing-registered trucks did not show lower value than those from other regions. Unlike black carbon, there is no clear correlation between emission controls and NO x emissions from the sampled on-road trucks. Further analysis shows that trucks with high BC EFs do not usually have high NO x EFs, and vice versa, indicating that the current emission standards implemented in Beijing and nationwide have only limited impact on NO x emissions control. Therefore, effective multi-pollutant control strategies and in-use compliance programs are imperative to reduce the overall emissions from the transportation sector. [ABSTRACT FROM AUTHOR]

Abstract: The period of the 2008 Olympic Summer Games in Beijing can be considered as a unique opportunity to study the influences of emission reduction measures on air quality improvement. Within this study atmospheric particles of different size classes (2.5 to 80μm) were investigated before, during, and after the Olympic Games period in order to observe and assess the success of short-term measures to mitigate extreme urban aerosol pollution and also to investigate, which particle size classes were reduced most effectively. Furthermore, black carbon (BC) concentrations in fine particles (PM2.5) during the source control period were compared to those of the previous years in order to investigate the decrease of combustion-derived aerosols. It is shown that besides the implemented mitigation measures precipitation decisively contributed to a considerable decrease of particulate air pollution in Beijing compared to the respective concentrations during the time directly before and after the Olympic Games, and also compared to average August concentrations during the previous years and the following year 2009. Particles of the fine fraction of the coarse mode (2.5 to 5μm), which have a residence time in the order of several days and which, therefore, are typically transported over long distances from outside of Beijing, were less efficiently reduced than coarser particles. This indicates that long-range transport of atmospheric particles is difficult to control and that presumably the established mitigation area was not large enough to also reduce the fine fraction of the coarse mode more efficiently. Furthermore, the study showed that coarse geogenic particles, which originated to a high percentage from construction sites and resuspension processes due to traffic seemed to be reduced most efficiently during the Olympic Games period. [Copyright &y& Elsevier]

Abstract: This paper reports findings of a recent field study that characterized the on-road emissions of individual diesel vehicles in and around Beijing, China during November and December of 2009. We successfully sampled 230 individual trucks on 4 major expressways around the city as well as 57 individual buses in the city using refined mobile chasing techniques and fast response instruments. Emission factors (EF) for carbon monoxide (CO), black carbon (BC) and particulate matter with diameters less than 0.5 μm (PM0.5) are derived from the measurements, which are consistent with the results from laboratory dynamometer tests. The PM0.5 number emission factor distributions demonstrate consistent bimodal modes with peaks around 10 nm and 80 nm, while the mass emission factor distributions demonstrate a unimodal maximum around 110 nm for a majority of the trucks. The BC emissions are shown to be highly correlated with the mass emission of particles with 100–250 nm diameters, which are in good agreement with the results from previous studies. A number of important policy implications are discussed based on the results from this study. First, we identified “heavy emitters” in the on-road fleet we encountered, finding that 5% of diesel trucks in this sample are responsible for 50% of total BC emissions, and 20% of the trucks are responsible for 50% CO and PM0.5 number emissions, 60% PM0.5 mass emissions and over 70% of BC emissions. This suggests that emissions control programs should include identifying and removing heavy emitters from the road or improving their emissions. Second, the BC and PM0.5 number emission factors of trucks registered in regions outside Beijing are significantly higher than those of Beijing-registered trucks, suggesting that improving engine and fuel standards in Beijing alone is not sufficient in reducing the traffic-related air pollution in Beijing. Third, the significantly lower emissions from Euro IV and CNG buses compared to the Euro II and Euro III buses support that introducing clean-burning buses is an effective way to reduce the overall vehicle emissions for the pollutants studied. Fourth, our refined chasing method demonstrates a cost-effective approach to characterize the emissions from a large number of on-road diesel vehicles. Further studies with large sample sizes are critical to constructing more accurate mobile emission inventories to represent the on-road vehicle population. [Copyright &y& Elsevier]

Abstract: The concentrations of black carbon (BC), total organic carbon (TOC) and polycyclic aromatic hydrocarbons (PAHs) have been determined in soils from urban and rural areas of Beijing. The rural area can be divided into plain and mountainous areas which are close to and relatively far from the urban area, respectively. Concentration of BC (5.83±3.05mgg−1) and BC/TOC concentration ratio (0.37±0.15) in Beijing’s urban soil are high compared with that in world background soils and rural soils of Beijing, suggesting the urban environment to be an essential source and sink of BC. Concentration of BC in the urban area decreases from the inner city to exterior areas, which correlates with the urbanization history of Beijing and infers accumulation of BC in old urban soils. Black carbon in Beijing soils mainly comes from fossil fuel combustion, especially traffic emission. Median PAH concentration in the urban area (502ngg−1) is one order of magnitude higher than that in the rural plain (148ngg−1) and mountainous area (146ngg−1) where PAHs are supposed to mainly come from atmospheric deposition from the urban area. Concentrations of BC correlate significantly with those of PAHs (p <0.01, except naphthalene) in the urban area and with those of heavier 4-, 5- and 6- ring PAHs (p <0.01) in the adjacent rural plain area, while there is no significant correlation with any PAH in the farther rural mountainous area. [ABSTRACT FROM AUTHOR]

Abstract: The concentrations of dichlorodiphenyltrichloroethanes (DDTs) were investigated for urban soil samples collected from business area (BU), classical garden (CL), culture and educational area (CU), large public green space (LA), residential area (RE), and roadside area (RO) in Beijing. The DDTs concentrations ranged from 0.03 to 1282.58ng/g, with an average of 68.14±189.46ng/g. The DDTs concentration in CL was much higher than that in the other five types of land use, which was due to the usage of DDTs to protect vegetation in CL, and the DDTs concentration was affected by both the usage history of DDTs and the age of the CL. Only 22% of the samples, mainly located in RO, manifested the application of technical DDTs recently. DDTs concentration showed a decreasing trend from the city center to the suburb, and it increased with the age of the urban area. DDTs were positively correlated with total organic carbon and black carbon in soils. About 81.7% of the samples met the grade I standard (50ng/g soil) of the Chinese Environmental Quality Standard for Soils, and only 1.5% of the samples exceeded the grade III standard (1000ng/g soil). [Copyright &y& Elsevier]

Abstract: The aggressive traffic interventions and emission control measures implemented to improve air quality during the 2008 Beijing Olympic Games created a valuable case study to evaluate the effectiveness of these measures on mitigating air pollution and protecting public health. In this paper, we report the results from our field campaign in summer 2008 on the on-road emission factors of carbon monoxide, black carbon (BC) and ultrafine particles (UFP) as well as the ambient BC concentrations. The fleet average emission factors for light-duty gasoline vehicles (LDGV) showed considerable reduction in the Olympic year (2008) compared to the pre-Olympic year (2007). Our measurement of Black Carbon (BC), a primary pollutant, at different elevations at the ambient site suggests consistent decrease in BC concentrations as the height increased near the ground level, which indicates that the nearby ground level sources, probably dominated by traffic, contributed to a large portion of BC concentrations in the lower atmospheric layer in Beijing during summertime. These observations indicate that people living in near ground levels experience higher exposures than those living in higher floors in Beijing. The BC diurnal patterns on days when traffic control were in place during the Olympic Games were compared to those on non-traffic-control days in both 2007 and in 2008. These patterns strongly suggest that diesel trucks are a major source of summertime BC in Beijing. The median BC concentration on Olympic days was 3.7 μg m−3, which was dramatically lower than the value on non-traffic-control days, indicating the effectiveness of traffic control regulations in BC reduction in Beijing. [Copyright &y& Elsevier]

In Beijing, the probability of snowfall is decreasing as a result of global warming. At the same time, Beijing has suffered severe air pollution. In this paper, the concentration and particle size characteristics of BC (Black Carbon) in snow during the winter of 2015 in Beijing were analyzed by the SP2 method. The average concentration of BC in snow meltwater in Beijing is 82 ng/mL, with a minimum value of 62.9 ng/mL and a maximum of 210.6 ng/mL. The BC particle size in snow and ice in the Beijing area is mostly concentrated in the range of 70–400 nm. After log-normal, the BC particle size above 600 nm is still small, which should be closely related to the nature of the local BC emission source. The concentration of BC in snow is highly susceptible to meteorological conditions and local pollution levels. When Beijing is under the control of the east wind or the southeast wind, aerosols in the urban areas can easily accumulate in the northwestern mountains and then settle or participate in the snowfall process, resulting in an increase in BC aerosol accumulation in the snow, thus further changing the optical properties of snow in the Beijing area. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is the most important aerosol light-absorbing component, and its effect on radiation forcing is determined by its microphysical properties. In this study, two microphysical parameters of refractory BC (rBC), namely, size distribution and mixing state, in urban Beijing from 2013 to 2019 were investigated to understand the effects of source changes over the past years. The mass equivalent diameter of rBC (D c) exhibited bimodal lognormal distributions in all seasons, with the major modes accounting for most (>85%) of the rBC masses. The mass median diameter (MMD) was obviously larger in winter (209 nm) than in summer (167 nm) likely due to the contribution of more rBC with larger D c from solid fuel combustion and enhanced coagulation of rBC in polluted winter. More rBC particles were thickly coated in winter, with the number fraction of thickly coated rBC (f coatBC) ranging within 29%–48% compared with that of 12%–14% in summer. However, no evidential increase in BC light-absorption capability was observed in winter. This finding was likely related to the lower absorption efficiency of larger rBC in winter, which partly offset the coating-induced light enhancement. Two stage of decreases in MMD and f coatBC were observed, accompanied with a persistent decrease in rBC loading, thereby reflecting the discrepant effects of source control measures on rBC loading and physical properties. The control measures in the earlier stage before 2016 was more efficient to reduce the rBC loading but slightly influenced the microphysical properties of rBC. As of 2016, the reduction in rBC concentration slowed down because of its low atmospheric loading. However, rBC showed a more obvious decrease in its core size and became less coated. The decrease in f coatBC may have weakened the BC absorption and accelerated the decrease in light absorption resulting from the reduction in rBC loading. Image 1 Decreases in BC core size and coating fraction were observed in Beijing from 2013 to 2019 in response to clean air actions. [ABSTRACT FROM AUTHOR]

Worldwide epidemiological studies have demonstrated that short-term associations of particulate matter (PM), might be further complicated by ambient temperatures, and increase human mortality. In China, among various PM indices, the health effects of black carbon (BC) are less understood due to the lack of data availability. Additionally, it is unclear how temperature modifies simultaneous and adverse effects of BC, and fine (PM size <2.5 μm; PM 2.5), and coarse particles (PM 2.5-10), on mortality outcomes. We adopted time-series Poisson generalized additive models to investigate temperature modifying effects on the association between three different PMs (BC, PM 2.5 , and PM 2.5-10) and mortality (non-accidental, respiratory and cardiovascular mortality) in Beijing, China, from 2010 to 2016. Average daily BC, PM 2.5 , and PM 2.5-10 concentrations were 4.95, 72.3, and 52.1 μg/m3, respectively, which were all significantly associated with daily mortality. High temperature strongly amplified effects of BC, PM 2.5 , and PM 2.5-10 on human mortality, especially BC effects that were most pronounced at >28 °C. Harmful effects were estimated for increases in non-accidental, respiratory, and cardiovascular mortality per interquartile increments in BC (4.11 μg/m3), PM 2.5 (62.37 μg/m3), and PM 2.5-10 (46.71 μg/m3) concentrations from the moving average of current and previous day (lag01) under high temperature (>28 °C). Mortality increases in non-accidental, respiratory, and cardiovascular categories were 5.12% (95% confidence interval [CI]: 4.79, 5.45), 7.41% (95%CI: 6.42, 8.40), and 6.36% (95%CI: 2.45, 10.3) for BC; 3.85% (95%CI: 3.27, 4.43), 6.64% (95%CI: 5.63, 7.65), and 4.54% (95%CI: 3.31, 5.78) for PM 2.5 ; and 2.56% (95%CI: 1.45, 3.67), 3.41% (95%CI: 1.53, 5.29), and 3.19% (95%CI: 2.44, 3.94), for PM 2.5-10 , respectively. These findings suggest that controlling the emission of ambient particles, especially BC, and improving air quality during summer would substantially benefit population health. Furthermore, BC should be considered as a crucial air quality indicator to reflect PM health risk. Image 1 • To test the synergistic effects of temperature and black carbon (BC) on mortality. • High temperature amplified the harmful effects of BC and PM on mortality. • The modifying effects of temperature on BC were different from that on PMs. [ABSTRACT FROM AUTHOR]