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During the Lunar New Year of 2020, the Chinese government implemented a strict nationwide lockdown to prevent the spread of the COVID-19, which may have led to changes in the distribution of pollutants. To enhance our understanding of the three-dimensional evolution of pollutants under special control scenarios, this study used vehicle lidar to obtain vertical profiles of aerosols and ozone (O 3) in Wuhan during the pandemic. Combined with ground observations and WRF-Chem model simulation results, we explored the evolution characteristics of pollutants. The results showed that the fine particulate matter (PM 2.5) concentration near the ground in Wuhan City was significantly reduced (40%) during the emission control period. The aerosol concentration decreased rapidly with an increase in height, and the maximum loading height was consistent with the atmospheric boundary layer height. Conversely, due to factors such as the reduction of the precursor nitrogen dioxide (NO 2) and rising temperatures, the near-ground O 3 concentration increased by 59%. Despite the significant reduction in emission sources, lidar observations still captured distinct aerosol transport layers on March 7 and March 10, 2020. These transport layers gradually descended, affecting the ground-level aerosol concentration. Additionally, one typical process of O 3 external transport was observed in the vertical direction. Our study provides a theoretical basis for a deeper understanding of the spatiotemporal distribution characteristics of pollutants during special control scenarios, aiding policymakers in formulating effective air pollution control strategies. • Pollutant 3D evolution first analyzed using mobile vehicle-lidar during Wuhan's emergency control period. • The aerosol concentration decreased, and the concentration decreased with increasing altitude. • Despite the reduction in emissions, the ozone concentration increased. • External transport of pollutants was observed during the control period. [ABSTRACT FROM AUTHOR]

Aerosols are not only an important component of the atmosphere, but also an indispensable medium for the generation of diffuse radiation (DR) in the atmosphere. This study analyzed the variation of diffuse radiation using ground-based observation under clear sky conditions at Wuhan, and quantifies the effects of aerosol optical and microphysical properties on diffuse radiation under blowing dust and haze conditions. The results are as follows: DR showed a decreasing trend from 2010 to 2014, and an increasing trend with rate of 4.076 W m-2 year−1 from 2014 to 2018. From 2011 to 2016, the diffuse radiation fraction (DRF) showed a trend of first decreasing and then increasing. During the study period, the relationship between aerosol optical depth (AOD) and DRF showed a significant and solid relationship with an R2 of 0.874. DR increased from 159.592 W m−2 in clean air to 195.420 W m−2 during the haze period, and AOD also increased from 0.607 in clean air to 0.914 during the haze period, which demonstrated the increase in diffuse radiation with the increase in aerosol loading. During the haze period, the sensitivity of fine-mode aerosol effective particle size (REFFF) and asymmetry (ASY) to DR was higher, with determination coefficients of 0.541 and 0.317, respectively, which were attributed to the hygroscopic growth of the aerosol resulting in larger particle size, increased ASY, and scattering of more solar radiation. The absorption properties of aerosols affect the DR during blowing dust, with a coefficient of determination between single scattering albedo (SSA) and DR of 0.40. The aerosol diffuse radiation effect (ADRE) was 111.688 W m−2 during the clean air period, ADRE increased by 31.839, 13.312 W m−2 during the haze and blowing dust periods, respectively, compared to that during the clean air period. The study of aerosols and radiation under different pollution conditions helps to understand the mechanisms behind local climate change and pollution phenomena, and deepens our understanding of the impact of pollution on the environment. • Long-term observations of solar diffuse radiation. • Contribution of aerosols to diffuse radiation during haze and dust events. • Changes in aerosol properties during blowing dust and haze periods. [ABSTRACT FROM AUTHOR]

Large amounts of aerosol in the atmosphere can cause significant attenuation of photochemical radiation and have a substantial impact on ozone and other secondary pollutants involved in photochemical reactions. This study examines the impact of aerosol actinic radiative effect on ozone and secondary pollutants during typical haze processes in the Pearl River Delta (PRD) region. The investigation employed lidar data and Weather Research Forecast–Community Multiscale Air Quality (WRF-CMAQ) modeling system. The results revealed that the aerosol caused a significant decrease in ground-level photolysis rates of NO 2 and ozone by 22% and 29%, respectively, when haze pollution was severe. The actinic radiative effect of aerosol caused an average reduction of more than 10 ppb in ground level ozone concentration in the PRD, with the core area experiencing a maximum reduction of 30 ppb. Additionally, the core area witnessed a maximum reduction of 2 ppb in peroxyacetyl nitrate (PAN) and 2 μg/m3 in PM 2.5. Due to reduced photolysis rates, nitrogen oxides increased by more than 5 ppb on average, reaching up to 10 ppb, while volatile organic compounds (VOCs) increased by a maximum of 10 ppb in the core region. Temporally, the aerosol actinic radiative effect was most pronounced in the morning and less significant in the afternoon. • During severe haze periods, the aerosol reduced the photolysis rates of ground level NO 2 and O 3 by 22% and 29%, respectively. • Aerosol actinic radiative effect reduced O 3 and PM 2.5 concentration but increased NOx, VOCs and nitrate in the haze process. • Aerosol actinic radiative effect during haze partially offset the positive feedback formed by its direct radiative effect. [ABSTRACT FROM AUTHOR]

Various combustion processes occur concurrently during biomass burning events, emitting a complex mixture of particulate and gaseous pollutants into the atmosphere. These emissions undergo chemical transformations facilitated by factors such as solar radiation and cloud formation, thereby altering the composition of aerosols. Additionally, these pollutants can affect the region of origin and neighboring countries, presenting regional and global environmental challenges. Therefore, precise evaluation of the particulate and gaseous pollutants emitted during biomass burning is essential to formulate effective management strategies. This study aimed to assess the concentration and chemical characteristics of particulate matter emitted during biomass burning in South Korea. On June 7, 2021, a research flight was conducted utilizing a High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a Single Particle Soot Photometer (SP2) for airborne measurements over South Korea inland areas. For data analysis based on administrative regions, the flight path was divided into four major areas (Areas A, B, C, and D). During the research flight, evidence of biomass burning events was observed primarily in Area C. A positive matrix factorization (PMF) analysis categorized the organic aerosols (OA) into five factors: biomass burning OA (BBOA), hydrocarbon-like OA (HOA1, HOA2), low-oxidized oxygenated OA (LO-OOA), and more-oxidized OOA (MO-OOA). Across all areas, MO-OOA accounted for the highest proportion of aerosols, whereas BBOA dominated in Area C at 23.8%, indicating the significant influence of biomass burning in this region. Instead of running a PMF analysis with all measurement data, a BBOA formula was derived from the previous study and this one. This allows us to estimate BBOA concentration without running PMF. • Airborne measurements studied biomass burning impact on air quality in South Korean agricultural regions. • High organics and rBC concentrations were found in agricultural areas, with markers indicating agricultural residue burning. • Organic biomass burning marker C 2 H 4 O 2 +(m/z 60) shows a stronger correlation than inorganic marker K+(m/z 39). • Continuous management and monitoring of biomass burning are the keys that are necessary to mitigate air quality. [ABSTRACT FROM AUTHOR]

The vertical structure of meteorological elements, black carbon (BC), and aerosols were in situ characterized by the King Air 350 aircraft measurements over the northeast of China during an East Asian dust storm event from April 10 to 13, 2023. The main causes of this dust storm event were the strong winds generated by the Mongolian cyclone, the cold front on the ground provided dynamic conditions, and the unstable atmospheric state provided thermal conditions and less precipitation in the dust source areas led to exposed the ground surface. The number concentrations of BC and aerosol had significant vertical distribution. The number concentration of aerosol in the dust storm (DS) layer increased rapidly with height, while the number and mass concentrations of BC were higher and varied slightly with height. The BC core mass median diameters (MMD) first increased with height, reaching a maximum value of 0.24 μm at 3000 m; and it rapidly decreased to 0.18 μm at 3200 m and then varied slightly with height above 3200 m. BC's bulk relative coating thickness (coated diameter divided by uncoated core diameter Dp/Dc) first decreased with height, reaching a minimum value of 1.16 at 3000 m, then increased with height, reaching a maximum of 1.38 (4250 m). A wind shear layer (7.9 m s−1 at 1850 m) with a sudden drop in temperature (the cooling rate can reach 7.4 °C·(100 m)−1) at 1900 m hinders the transportation of dust particles to the ground, allowing the dust particles to be transported at long-term distances. There were two stratifications in the dust storm layer: DS1 (1700–3000 m, the vertical wind speed was downward, the horizontal wind speed was small) and DS2 (3000–4500 m, the vertical wind speed was upward, the horizontal wind speed was large). The distinct atmospheric flow field conditions between DS1 and DS2 led to different BC and aerosol pollution characteristics. In DS2, the number concentrations of BC and aerosol were higher, the aging ratio of BC particles was higher, and the size of the core particle of BC was smaller. The concentrations of BC, aerosol, Dp/Dc, and MMD in DS2 were 1.1, 59.0, 1.02, and 0.84 times higher than those in DS1, respectively. Dust particles transported over long distances were primarily small. The number concentrations of aerosols at 0.1–0.12 μm and 0.1–0.24 μm were higher in DS1 and DS2, respectively. Still, the number concentration of aerosol at 0.12–0.28 μm in DS1 was lower than in the planetary boundary layer (PBL) and residual layer (RL). [Display omitted] • Aircraft in situ observations of aerosol and BC during the East Asian dust storm. • Two dust layers: Dust Storm (DS)1/DS2 (vertical wind speed (WS) downward/upward, horizontal WS small/large). • Wind shear layer with T sudden drop at 1900m hinders dust transport to ground. • Dust particles were mainly small particles (0.1–0.24 μm) during the long-term distance transport. [ABSTRACT FROM AUTHOR]

Satellite-based aerosol optical depth (AOD) products are commonly used in various aerosol-related studies, such as aerosol pollution mapping and aerosol-climate interactions. However, these satellite AOD products often suffer from significant missing gaps due to cloud cover and limitations in the retrieval algorithm. To address this issue, some studies take advantage of real-time seamless simulation of numerical models and successfully fill in these gaps by establishing a regression relationship between satellite AOD and numerical model AOD. However, these previous studies usually use satellite AOD retrievals as the regression target, which limits the accuracy of the imputation results by the original accuracy of satellite AOD retrievals and also consumes a considerable amount of time. To overcome these limitations, this study proposes a spatiotemporal imputation model called Bi-ConvRNN, which combines convolutional neural networks (CNN) and bidirectional recurrent neural networks (Bi-RNN). The model takes both satellite AOD retrievals and numerical model AOD data as input and utilizes the weighted mean squared error (MSE) loss function of multiple AOD datasets, e.g., ground-based data, satellite retrievals, and numerical simulation, as the optimization target to improve the imputation accuracy. The proposed model is evaluated using hourly COMS GOCI AOD products. In the independent test set, the AOD results generated by the Bi-ConvRNN model in the region containing GOCI AOD retrievals can break the accuracy of original GOCI AOD products with the accuracy improved from R2 = 0.70 [RMSE = 0.15] to R2 = 0.84 [RMSE = 0.11], and the filling accuracy, e.g. R2 = 0.79, [RMSE = 0.14], in the region without GOCI AOD retrievals are still better than those of the original GOCI AOD retrievals. Additionally, the Bi-ConvRNN model demonstrates satisfactory filling efficiency, requiring only 0.12 s to fill in the missing gaps of hourly GOCI AOD products per day. These results highlight the efficiency and reliability of the proposed model in filling the gaps in satellite AOD products, and the filled AOD results have great potential for further aerosol-related research. • An imputation model for missing gaps in hourly satellite AOD products is proposed. • The imputation model merges accurate AERONET AOD and seamless numerical model AOD. • The imputation model breaks through the accuracy limitation of satellite AOD data. • The imputation model achieves a high efficiency to fill hourly GOCI AOD data. [ABSTRACT FROM AUTHOR]

The ongoing Russia-Ukraine war has an impact on air quality in the contested region, but it is difficult to assess it during the war and to distinguish between weather conditions and anthropogenic impacts on air pollution. Aerosol optical depth (AOD) might be a way to indicate the regional air quality remotely. In this study, we analyze satellite-based MODIS Multi-Angle Implementation of Atmospheric Correction (MAIAC) AOD products to compare monthly mean AOD values before and during the war. By examining the spatial-temporal distribution of AOD in 2022 and comparing it with a baseline period from 2012 to 2021, we aim to assess the impact of the conflict. Our analysis employs a time series algorithm that decomposes long-term trends and seasonal variations, enabling us to identify AOD changes associated with the war-induced artificial perturbations. Additionally, we utilize satellite-based tropospheric NO 2 data and nighttime lighting data as auxiliary sources to support the analysis of abnormal AOD changes resulting from the war. Furthermore, four parameters from Aerosol Robotic Network (AERONET) measurements in the Kyiv site, including angstrom exponent (AE), single scattering albedo (SSA), refractive index (RI), fine mode fraction (FMF) were exclusively discussed to explore the possible changes of aerosol physical-optical properties over Ukraine during the war. Results showed that air quality in Ukraine has been affected by the war in contradictory ways at different levels. At the national level, atmospheric pollution has dropped across Ukraine due to a decrease in the sources of air pollution emissions as a result of the suppression of economic and agricultural activities. Meanwhile, atmospheric air quality has deteriorated at the local scale where war is intense due to the large amounts of air pollutants emitted by explosions. Specifically, a significant decrease in AOD of 22.46% compared to the baseline period was observed across Ukraine in January and February 2022 before the war. Additionally, there was a column density reduction of over 10% for tropospheric NO 2 compared to the same period in the previous year. Following the outbreak of the war on February 24, significant increases in AOD were observed in March when compared to the baseline period. Eastern Ukraine experienced a significant increase of 40.14%, while northern Ukraine and central Ukraine saw rises of 34.15% and 45.78%, respectively. In April, a wider distribution of areas with significantly high AOD values across Ukraine was observed compared to March. In July, widespread areas with anomalous low AOD appeared in northern and western Ukraine, likely due to a decrease in post-harvest agricultural burning caused by the war. In August, anomalous high AOD areas were observed in central Ukraine, possibly attributed to continued Russian long-range strikes and a new round of bombardments. • Air quality in Ukraine was affected by the war in contradictory ways at the national and local levels. • Abnormally low AOD occurred at the national scale due to decreased industrial production and agricultural burning. • Abnormally high AOD was observed at the local scale where the war was intense. • Use MAIAC AOD to assess the war objectively and provide consistency checks with previous studies using sample data. [ABSTRACT FROM AUTHOR]

The Arctic region is warming about four times faster than the rest of the globe, and thus it is important to understand the processes driving climate change in this region. Aerosols are a significant component of the Arctic climate system as they form ice crystals and liquid droplets that control the dynamics of clouds and also directly interact with solar radiation, depending on the compositions and mixing states of individual particles. Here, we report on the characteristics of submicron-sized aerosol particles using transmission electron microscopy obtained at two high Arctic sites, northeast Greenland (Villum Research Station) and Svalbard (Zeppelin Observatory), during spring 2018. The results showed that a dominant compound in the submicron-sized spring aerosols was sulfate, followed by sea salt particles. Both model simulations and observations at the Zeppelin Observatory showed that sea salt particles became more prevalent when low-pressure systems passed by the station. Model simulations indicate that both sampling sites were affected by diffused and diluted long-range transport of anthropogenic aerosols from lower latitudes with negligible influences of biomass burning emissions during the observation period. Overall, the composition of measured aerosol particles from the two Arctic sites was generally similar and showed no apparent variation except for the sea salt fractions. This study shows a general picture of high Arctic aerosol particles influenced by marine sources and diffused long-range transport of anthropogenic sources during the Arctic spring period. These results will contribute to a better knowledge of the aerosol composition and mixing state during the Arctic spring, which helps to understand the contributions of aerosols to the Arctic climate. [Display omitted] • Electron microscopy reveals composition and mixing state of submicron aerosol particles in the Arctic spring. • Sea salt particles demonstrate a size-dependent increase and exhibit correlations with specific elements. • Regional Arctic aerosol particles mainly from marine sources and diffused long-range transport are shown. [ABSTRACT FROM AUTHOR]

Recent studies in the direction of identifying signatures of aerosol emission from fireworks stressed on the need of simultaneous measurements of mass, number and chemical compositional characteristics. Such an identification is tricky when the measurements are performed in an elevated background environment and/or in presence of an additional wide source term. This work studies the modifications in atmospheric aerosol characteristics due to firework induced emissions in Bathinda city of Punjab, North India. This study presents interpretations based on the results obtained from the measurements performed for 14 days covering the days of Diwali festival, 2021 as well as the baseline database gathered from a year-long campaign to measure mass concentration in different size-ranges. Highest mass concentration for the study duration was observed to be PM10- 382 μg/m3, PM2.5–299 μg/m3, PM1- 240 μg/m3, respectively in the month of November 2021. A clear increase of concentration was noted for Diwali days and the averaged concentration for PM10, PM2.5 and PM1 reached to 445 μg/m3, 363 μg/m3 and 304 μg/m3 on Diwali day, respectively. Number size distribution evolution analysis for the data measured from an optical particle counter (size range: 0.25–1 μm) showed that emissions for Diwali days occurred mostly at night times and in smaller size channels (<0.5 μm). Chemical compositional data of selected samples close to Diwali days was interpreted in terms of factor of increase of mass density of collected particles in different size-ranges. Mass density of elements K, Cl, S, Al, Zn, P, Mn, Pb, Br and Zr in PM1 samples was observed to be higher for Diwali days in comparison to their pre-Diwali levels. Few elements viz. Ba, Sr and Nb were found to be only present in the samples taken during Diwali days. In addition to Ba, Sr and Nb, elements V, Mg, Br and Se were observed to be present in PM2.5 and PM10 samples taken during the Diwali days. This study provides combined ambient aerosol characteristics during Diwali days when the air quality was affected by stubble burning as well. [Display omitted] • Size segregated aerosol measurements during fireworks at a site affected by stubble burning. • PM10, PM2.5 and PM1 were 445 μg/m3, 363 μg/m3 and 304 μg/m3, respectively on Diwali day. • Emission of particles in size range <0.5 μm during evening-night times attributed to fireworks. • Increase of elemental mass density and introduction of new elements captured in different size-ranges. [ABSTRACT FROM AUTHOR]

Carbonyl compounds exist in the atmosphere as either gases or aerosols. Some of them are water soluble and known as oxidation products of biogenic and/or anthropogenic hydrocarbons. Five carbonyl compounds, glyoxal (GO), 4-oxopentanal (4-OPA), glycolaldehyde (GA), hydroxyacetone (HA) and methylglyoxal (MG) have been identified in a temporal series of 12 rain samples. The concentrations of the compounds in the samples were high at the beginning of the rain event and decreased with time to relatively low and fairly constant levels, indicating that the compounds were washed out from the atmosphere at the start of the rain event. Possibly, these compounds also existed in the cloud condensation nuclei (CCN). Wet deposition rates of the carbonyl compounds were calculated for nine samples collected during a 20 h period. The deposition rates ranged from 0 (4-OPA) to 1.2×10-1 mg C m-2 h-1 (MG) with the average of 2.9×10-2 mg C m-2 h-1. Production rates of isoprene oxidation products (GA, HA and MG) in the area surrounding the sampling site were estimated with a chemical box model. The deposition rates exceeded the production rates in most samples. This indicates that the rainfall causes a large net flux of the water soluble compounds from the atmosphere to the ground. Insoluble carbonyl compounds such as n-nonanal and n-decanal were expected to be present in the atmosphere, but were not detected in the rain during the sampling period, suggesting that an aerosol containing these insoluble compounds does not effectively act as a CCN. © 2006 Elsevier Ltd. All rights reserved.

Empirical equations were developed and applied to predict losses of 0.01-100 mum airborne particles making a single pass through 120 different ventilation duct runs typical of those found in mid-sized office buildings. For all duct runs, losses were negligible for submicron particles and nearly complete for particles larger than 50 mum. The 50th percentile cut-point diameters were 15 mum in supply runs and 25 mum in return runs. Losses in supply duct runs were higher than in return duct runs, mostly because internal insulation was present in portions of supply duct runs, but absent from return duct runs. Single-pass equations for particle loss in duct runs were combined with models for predicting ventilation system filtration efficiency and particle deposition to indoor surfaces to evaluate the fates of particles of indoor and outdoor origin in an archetypal mechanically ventilated building. Results suggest that duct losses are a minor influence for determining indoor concentrations for most particle sizes. Losses in ducts were of a comparable magnitude to indoor surface losses for most particle sizes. For outdoor air drawn into an unfiltered ventilation system, most particles smaller than 1 mum are exhausted from the building. Large particles deposit within the building, mostly in supply ducts or on indoor surfaces. When filters are present, most particles are either filtered or exhausted. The fates of particles generated indoors follow similar trends as outdoor particles drawn into the building. (C) 2003 Elsevier Ltd. All rights reserved.

The size-resolved chemical composition and mixing state of single particles were observed by using single particle aerosol mass spectrometry (SPAMS) from May 12 to June 8, 2017. A total of 979,899 particles were successfully ionized to identify 6 main particle groups including carbon-rich particles (47.66%), K-rich particles (28.78%), heavy-metal particles (10.12%), sodium particles (8.86%), dust particles (3.89%), and ammonium particles (0.67%). The wind direction and speed had large impacts on the proportion of carbonaceous aerosol particles and had little influence on heavy-metal particles. The relative humidity (RH) had great impacts on the chemical components of aerosol particles. The proportion of secondary particles increased, while the primary particles diminished as RH increased. The proportion of carbon-rich particles decreased with increasing particle size. However, the size distributions varied significantly for different types of carbonaceous particles. Sodium particles and heavy-metal particles were mainly concentrated at sizes larger than 1 μm. K-rich particles had a maximum proportion at 0.5–1.0 μm. The number fraction of ammonium particles predominated chiefly at 0.6–2.0 μm. It has been found that aerosol particles, mainly from burning processes, were mixed with 36 [C 3 ]+ to different degrees at Mt. Tai. A high proportion of ammonium particles were mixed with organics and elemental carbon (OCEC), elemental carbon-sulfate (EC-sulfate), and elemental carbon-secondary (EC-secondary) particles, while few of these particles were mixed with EC-nitrate particles, which indicated that the ammonia in the air was inclined to combine with organic species and sulfate. A higher proportion of atmospheric particles mixed with nitrate were observed compared to those mixed with sulfate. Image 1 • SPAMS was used for the first time to observe at Mt. Tai. • The proportion of primary/secondary particles diminished/increased as RH increased. • Higher proportions of particles mixed with nitrate than with sulfate. [ABSTRACT FROM AUTHOR]

The causal link between ambient PM 2.5 and adverse health effects is still not clear enough, nor it is clear what factors (physical and/or chemical) contribute to PM 2.5 toxicity and by what mechanism(s). With a view on this, we launched the CARE experiment, during which we performed a comprehensive characterisation of the physicochemical properties of fine and ultrafine particles under exposure levels dominated by the urban combustion aerosol, and their toxicological assessment through in-vitro tests (lung epithelia cells cultured at the ALI) directly under ambient conditions, oxidative potential (determined through 2′,7′-dichlorouorescin, OP DCFH ), and human biomonitoring. We already reported about aerosol characterisation, and in-vitro model results during CARE. Building upon these, in this work we assess the combustion aerosol oxidative response through the analysis of consistency between the three independent aerosol oxidative responses obtained, and the exploration of any causality link with the combustion aerosol. This is the first time to our knowledge that combustion related PM 2.5 physicochemical properties and its OP DCFH are compared to the cellular-oxidative response (C-OR) obtained through the PM in-vitro test carried out (for the first time) directly under atmospheric ambient conditions, and to certain biomarkers of oxidative damage to DNA/RNA (8-oxo-7,8-dihydroguanine, 8-oxo-7,8-dihydro-2′-deoxyguanosine and 8-oxo-7,8 - dihydroguanosine). Our results provide a first evidence of a combustion-dependent association between the in vitro C-OR, the PM 2.5 OP DCFH , and the urinary excretion of the 8-Oxo-7,8-dihydroguanosine. Yet this is not a substantial basis for drawing any cause-effect relationship. However, our findings support previous literature suggesting a link between combustion and oxidative response of PM 2.5. Moreover, we add a consistency across completely independent oxidative response measurements with a possible dependence on the combustion traffic-related aerosol. This is a piece of information that may have important implications in the understanding of how combustion sources contribute to oxidative response related diseases. Image 1 [ABSTRACT FROM AUTHOR]

The nocturnal, seasonal and intra-annual variation of vertical distribution of tropospheric aerosols over two nearby stations Gadanki (13.5oN, 79.2oE) and Tirupati (13.6oN, 79.4oE) is investigated using ground-based Micro Pulse Lidar (MPL) and space-borne Lidar (CALIPSO) systems during 2010–2017. The nocturnal variation of aerosol extinction (AE) coefficient reveal high AE below ∼2 km in midnight hours and aerosols are slowly descending towards the surface during early morning hours. From the seasonal variation, AE values are found to be higher at lower altitudes (<2 km) during winter and post-monsoon seasons, a sharp decrease with increasing altitude is found in tandem with boundary layer and low wind speeds. Interestingly, during monsoon season, significant aerosol loading is found in the altitude range of ∼2–5.5 km mainly due to the influence of strong Low Level Jet (LLJ). The clean environment observed below ∼2 km during this season is attributed to the wet scavenging, downward vertical winds and existance of no strong local source. The seasonal mean AE profile derived from CALIPSO matches well with the MPL in all the seasons except in monsoon season where a large bias is noticed below 2 km. The intra-annual variation revealed more than 80% of aerosols existing above (below) the boundary layer during monsoon (winter) months contribute to the total Aerosol Optical Depth (AOD). The depolarization ratio (>0.2) in the month of July shows the dominance of dust particles which includes long-range transport over this locations. Back trajectories reveals that potential sources are changing from season to season at different altitudes and confirms that the aerosols observed at higher altitudes are advected from other land and oceanic regions. Thus, aerosol vertical distribution is mainly controlled by meteorology and dynamics over this region. Further, the reasonably good correlation found between MPL and MODIS AODs suggests that MODIS could provide reliable AOD over land region also. • Lidar observed aerosol vertical distribution over Indian tropical stations show strong nocturnal and seasonal variation. • Aerosol extinction over Gadanki/Tirupati region is higher at altitudes <2 km during winter and post-monsoon seasons. • Significant aerosol loading is noticed around ∼2–5.5 km and clean environment below ∼2 km during monsoon. • The contribution of aerosols above (below) the boundary layer during monsoon (winter) is found to be around 80% to the total AOD. • Back trajectory analyses confirms the advection of aerosols from other land and oceanic regions to the observation site. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM 2.5) is known to have an adverse impact on public health and is an important climate forcer. Secondary organic aerosol (SOA) contributes up to 80% of PM 2.5 worldwide and multiphase reactions are an important pathway to form SOA. Aerosol-phase state is thought to influence the reactive uptake of gas-phase precursors to aerosol particles by altering diffusion rates within particles. Current air quality models do not include the impact of diffusion-limiting organic coatings on SOA formation. This work examines how α -pinene-derived organic coatings change the predicted formation of SOA from the acid-catalyzed multiphase reactions of isoprene epoxydiols (IEPOX). A box model, with inputs provided from field measurements taken at the Look Rock (LRK) site in Great Smokey Mountains National Park during the 2013 Southern Oxidant and Aerosol Study (SOAS), was modified to incorporate the latest laboratory-based kinetic data accounting for organic coating influences. Including an organic coating influence reduced the modeled reactive uptake when relative humidity was in the 55–80% range, with predicted IEPOX-derived SOA being reduced by up to 33%. Only sensitivity cases with a large increase in Henry's Law values of an order of magnitude or more or in particle reaction rates resulted in the large statistically significant differences form base model performance. These results suggest an organic coating layer could have an impact on IEPOX-derived SOA formation and warrant consideration in regional and global scale models. • Relative Humidity dependent D org showed limited effects on IEPOX reactive uptake. • Increasing inorganic and organic Henry's Law coefficients improved model performance. • Concentrating inorganic species into the aerosol core improved model performance. [ABSTRACT FROM AUTHOR]

Atmospheric aerosol levels are high in different regions of China. Changes in atmospheric stability and mixing layer height (MLH) may affect the vertical aerosol distribution during pollution events. Here, we continuous studied the spatiotemporal distribution of MLH in China over 2000–2013 to characterize the regional-scale properties of atmospheric boundary layers. MLH was larger in the Southern Coastal and Southeastern China (1241.5 ± 73.5 and 632.7 ± 61.8 m, respectively), but lower in Eastern and Southwestern China (518.1 ± 63.6 and 462.7 ± 88.5 m, respectively). We divided the monitoring stations into 11 regions; these regions could be classified into three types with an increasing linear trend (95% confidence level), with a decreasing linear trend (95% confidence level), and with fluctuation changes. In all regions, MLH was higher in spring and summer than in autumn and winter. The spatial distribution of the diurnal MLH increased significantly at 1400 BJT (Beijing time) in all regions, with the strongest radiation being noted during the daytime. Higher levels of PM 2.5 with corresponding lower MLH were noted during winter, indicating that lower MLH could confine the pollutant diffusion to near the surface. By contrast, in spring, higher MLH could be potentially due to the dynamic condition. In general, the poor air quality days occurred more frequently in winter than in other seasons. As the air quality worsened, most MLH showed a decreasing trend in almost all regions. This work provides information that aids in further understanding not only MLH distribution in China but also specific PM–MLH interaction to facilitate regional atmospheric environment monitoring and prediction. • Greater MLH was found in Southern and lower MLH in Southwestern China. • The annual MLH with increasing/declining/fluctuating trends were found. • Interaction between PM and MLH contributed to the regional air quality. [ABSTRACT FROM AUTHOR]

Abstract The irradiation under simulated sunlight of some phenolic compounds typically emitted in ambient air by biomass burning, namely vanillin and acetosyringone, yielded intermediates with humic-like fluorescence properties that can be assimilated to humic-like substances (HULIS). Evidence was obtained by ultra-high-resolution mass spectrometry of the occurrence of oligomerization processes up to the formation of trimeric species. In contrast, the irradiation of other biomass-burning compounds such as vanillic acid, m-cresol and guaiacol did not yield either HULIS-type fluorescence or oligomers. We suggest that the photolysis of biomass-burning compounds is a potential HULIS source in the atmosphere, if the relevant substrates undergo photoinduced oligomerization reactions. Graphical abstract Image 1 Highlights • Humic-like fluorescence is produced by irradiation of biomass-burning phenols. • Vanillin and acetosyringone are involved in the process. • Evidence of oligomerization, up to formation of trimeric species. • Norrish-type and phenoxyl reactions are reasonable oligomerization pathways. • This is a potential route to atmospheric humic-like substances (HULIS). [ABSTRACT FROM AUTHOR]

Abstract Size-resolved elemental measurements were conducted for the water-soluble fraction of particulate matter at a central California coastal city, Marina, during two separate summertime field campaigns: the Nucleation in California Experiment (NiCE) in 2013 and the Fog and Stratocumulus Evolution (FASE) campaign in 2016. Two Micro-Orifice Uniform Deposit Impactors (MOUDIs) were used to quantify mass size distributions of 29 elements and a Positive Matrix Factorization (PMF) model revealed six characteristic sources during the measurement periods: (i) Crustal Emissions (3.9% of total mass), (ii) Secondary Aerosol (24.4%), (iii) Biomass Burning (13.1%), (iv) Waste Facilities (8.7%), (v) Vehicular Emissions (4.4%), and (vi) Marine Emissions (45.4%). Characteristic elements from each of these sources included the following: (i) Crustal Emissions (Fe, Al, Ti, Pt), (ii) Secondary Aerosol (Zn, As, Rb, K, Cu, V), (iii) Biomass Burning (Rb, K, Cu, Pt), (iv) Waste Facilities (Ag, Cd, Ni, Al), (v) Vehicular Emissions (Zn, Zr, V, Mn), and (vi) Marine Emissions (Na, Sr, V, Mn). Temporally-resolved results revealed higher PM levels associated with Vehicular Emissions (day/night mass concentration ratio = 31.3), Crustal Emissions (day/night = 20.0), and Secondary Aerosol (day/night = 27.2) during the day compared to night due to some combination of more daytime anthropogenic activity, wind speed/directional factors, and photochemistry. The Marine Emissions factor exhibited a day/night concentration ratio of exactly 1.0. Mass size distributions revealed characteristic peaks in four diameter ranges: 0.1–0.18 μm, 0.32–0.56 μm, 1.0–1.8 μm, and 3.2–5.6 μm. The number of modes varied depending on the species and degree of wildfire influence, with additional differences observed between the NiCE and FASE wildfire periods. Graphical abstract Image 1 Highlights • Size-resolved measurements for 29 elements at a central California coastal site. • Six characteristic sources with marine emissions most influential on a mass basis. • Anthropogenic elements co-emitted with secondary aerosol precursor species. • Several elements enhanced during daytime owing to anthropogenic activity. • Common concentration modes: 0.1–0.18 μm, 0.32–0.56 μm, 1.0–1.8 μm, 3.2–5.6 μm. [ABSTRACT FROM AUTHOR]

Abstract Vertical variation in aerosol optical properties [e.g. Single Scattering Albedo (SSA) and aerosol extinction coefficient] over a polluted environment is extremely important for better understanding of columnar radiative characteristics. The present case study over a typical polluted environment (New Delhi) discusses the vertical profile (ground to 700 m) of modelled optical properties of atmospheric particles at different altitudes. Here, we used the aerosol physico-chemical data generated in the tethered balloon-based observation conducted at CSIR-NPL, New Delhi (28° 38′ 10″ N, 77° 10′ 17″ E) from 21st −27th February 2014. Based on the microscopic observations of individual particles, we developed the aerosol model shapes (coated spheres) for simulating their optical properties. Total three cases were considered for simulating the aerosol optics at varying altitude; Case A: External mixture of coated dust and coated sulfate particles; Case B: External mixture of coated dust, coated sulfate, coated OC (Organic Carbon) and coated EC (Elemental Carbon) (with assumption that 6% EC at ground level); Case C: External mixture of coated dust, coated sulfate, coated OC and coated EC (with assumption that 10% EC at ground level). At 550 nm wavelength, the value of SSA has been found to be highest (i.e. 0.985) at 200 m altitude for Case A while Case B (i.e. 0.9523) and Case C (i.e. 0.9291) show highest values at 500 m altitude. SSA was found to be maximum at 500 m altitude for both Case B and Case C due to the presence of lowest graphitic counts at that particular altitude. Case B and Case C exhibit similar pattern but differ in magnitude, this is due to two EC extremities at ground level i.e. minima (6%) and maxima (10%). The percentage deviation in SSA from ground level to 700 m was found to be highest for Case C (i.e. 5.95%) followed by Case B (i.e. 4.19%) and Case A (i.e. 1.4%). Modelled aerosol optical properties within boundary layer may improve our understanding about the thermodynamics of lower atmosphere. Highlights • A case study over a typical polluted environment (New Delhi) discusses the vertical profile of modelled optical properties of atmospheric particles at different altitudes. • The aerosol physico-chemical data (bulk and individual particle level) used to simulate the vertical profile of aerosol optical properties. • Better assessment of vertical profile of aerosol optical properties plays an important role in reducing the uncertainties associated with radiative forcing. • Frequent airborne observations will certainly provide statistically significant region-specific aerosol properties. [ABSTRACT FROM AUTHOR]

Abstract During the first Intensive Observation Period (IOP1) of the SHADOW (SaHAran Dust Over West Africa) campaign carried out during March–June 2015, the Mbour site (Senegal) was reinforced with a large setup of in-situ and remote sensing instruments to measure the aerosol optical, physical and chemical properties as well as the atmospheric dynamical features over the site. Here, we use this dataset to study the impact of Sea Breeze (SB) on the aerosol properties. Two case studies were selected: (i) one representative of SB events observed during typical Harmattan conditions, (ii) and one representative of SB events observed during a Harmattan desert dust event. Both cases show a strong influence of the SB period on the dry Mass Scattering Efficiency (MSE), which increases by a factor of up to 1.4. Given the fact that SB occurred every other day at this coastal site during IOP1 (dry season) and that the relative humidity may reach 96%, the effect of such event on the radiative forcing may not be negligible. In order to evaluate the effects of different flows on aerosol transport, recirculation and stagnation factors were retrieved from wind components. The air mass recirculation factor implies that aerosols previously transported from the land over the sea are then brought back inland. In both cases, high recirculation factors were calculated (between 0.84 and 0.98) and air mass stagnation was observed right before the SB establishment. However, this stagnation is observed over the sea during the first case while it is located near the coast during the second case, which has a significant impact on the aerosol evolution. Indeed, a stagnation of air masses over the sea is associated with an increase in fine aerosol mass concentrations (PM 1 , PM 2.5) due to a higher contribution of marine and anthropogenic sources notably for organic aerosols, and a higher contribution of more-oxidized organics. This contribution is lower when the air mass stagnation occurs over the shoreline during the desert dust event. Highlights • Local dynamics impact aerosol properties. Aerosol mass scattering efficiency is increasing during sea-breeze period. • The stagnation area, due to flow confrontation, over the sea (coastline) leads to an enhancement of PM1 (PM10) fraction. • During the Low Level Jet onset in altitude, PM 10 and absorption coefficient observed at ground level increased up to a factor of 2. [ABSTRACT FROM AUTHOR]

Abstract New particle formation (NPF) events are important phenomena that generate nanoparticles and even fine particles via gas-to-particle conversion. These events have clear effects on aerosol loading, atmospheric chemistry and global climate. Long-term field measurements were used to characterize aerosol size distributions and to examine the role of atmospheric volatile organic compounds (VOCs) in NPF events in the urban environment of Shanghai. Aitken and accumulation particles are dominant and account for 85–95% of the total particles, whereas coarse particles are negligible. Particles in the four size-models show the same seasonality: highest in winter and lowest in autumn. The mean particle size distributions display different patterns of diurnal fluctuation, including bimodal in spring and winter, tri-modal in autumn, and "banana" shaped in summer due to highly frequent NPF events. The geometric mean diameter (GMD) is often 20–30 nm or 40–60 nm. Overall, NPF events occur on 89 days out of 335 measurement days (26.5%), and the newly formed particles have a mean growth rate of 6.28 nm h−1. Two typical anthropogenic aromatics, benzene and toluene, from traffic emissions closely match the occurrence of NPF events and have a weakly positive correlation with the nucleation particle number concentrations. The enhanced VOCs as precursors of organic vapors may contribute to the growth process of NPF events to some extent (e.g., growth rate) so that newly formed particles can grow into a detectable size. Highlights • Aitken and accumulation particles account for 85–95% of total particles. • Aerosol size distributions display different diurnal patterns. • The NPFs occur on 89 days out of 335 days with the highest frequency in summer. • Two anthropogenic aromatics have correlations with nucleation particle. • Enhanced VOCs may contribute to the growth of newly formed particles. [ABSTRACT FROM AUTHOR]

Abstract New particle formation (NPF) and growth is an important phenomenon in terms of the global particle number concentrations. However, our knowledge about NPF events at the top of the boundary layer is particularly weak in heavily polluted conditions. In this study, the aerosol size distributions, black carbon (BC), chemical components of single particles, particulate matter (PM 2.5 and PM 10) and meteorological data were collected from May 12 to June 8, 2017 at the summit of Mt. Tai by using a wide-range particle spectrometer (WPS), Aethalometer (AE-33), a single particle aerosol mass spectrometer (SPAMS), a β-ray continuous ambient particulate monitor and an automatic weather station. Twelve new particle growth (NPG) events occurred during the observation period, accounting for 46.2% of the total observation days. The average relative humidity (RH) was 52% on NPF days and was 11.5% lower than the value on non-NPG days. The average temperature and wind speed were 18 °C and 5.3 m s−1 on NPG days, respectively, which were 12.2% and 18.9% higher than those on non-NPG days. The PM 2.5 concentration differed slightly on NPG and non-NPG days. However, the concentrations of PM 10 and BC were relatively high on NPG days, with average values of 88.0 μg m−3 and 1849.9 ng m−3, respectively, which were 1.2 and 1.3 times higher than those on non-NPG days. The NPG events had major influences on the size distributions of aerosol number concentration at 10–60 nm and surface area concentrations at 100–300 nm. During the NPG events, the average formation rate (FR), growth rate (GR), condensational sink (CS), vapor source rate (Q) and condensing vapor concentration (C) were calculated to be 1.30 cm−3 s−1, 14.54 nm h−1, 3.21 × 10−2 s−1, 7.34 × 106 cm−3 s−1 and 19.92 × 107 cm−3, respectively. The NPG events were influenced mostly by foreign transport processes and less impacted by local surrounding pollutants. The meteorological factors varied with different types of NPG events. The chemical components varied greatly during different types of NPG events. Sulfate had a small influence on three types of NPG events. Nitrate and ammonium had comparatively great impacts on local and southerly transport NPG events. The organic matters contributed more significantly to the northerly transport NPG events. Highlights • The characteristics of NPG events are examined at summit of Mt. Tai. • The concentrations of PM 10 and BC were relatively high on NPG days. • NPG impacted on spectral distributions of N at 10–60 nm and S at 100–300 nm. • Nitrate and ammonium (organic) had great impacts on local and southerly transport (northerly transport) NPG. [ABSTRACT FROM AUTHOR]

Abstract The present study uses 18 years (March 2000–May 2017) of satellite–derived relevant parameters to examine the impact of aerosols on cloud properties, radiative fluxes and ACI (aerosol-cloud interaction) over Indian region. The study includes consideration of shortwave cloud radiative forcing (SWCRF), longwave cloud radiative forcing (LWCRF) and net cloud radiative forcing (NetCRF) from CERES (Clouds and Earth's Radiant Energy System). Also, aerosol optical depth (AOD) and cloud properties such as ice/liquid CER (Cloud Effective Radius), CF (Cloud Fraction), COD (Cloud Optical Depth), CTP (Cloud Top Pressure) and ice/liquid CWP (Cloud Water Path; i.e., ICWP and LCWP) are also considered. Moderate to high aerosol loading and the significant increasing trend of AOD is observed over several parts of Indian region depending upon the seasons. CF is found to be moderate to higher during monsoon months with increasing trend over several parts of the country. Optically thicker high-level clouds have low SWCRF value; whereas, middle-level and low-level clouds have low to moderate SWCRF value. In the majority of cases, Twomey effect is observed whereas in some scenarios Anti-Twomey effect is seen. Highlights • Increasing trend of AOD is seen over most parts of India during all the seasons. • Optically thicker low and middle clouds have low to moderate SWCRF value. • Twomey effect seen in most of the scenarios whereas others show Anti-Twomey effect. • Positive ACI indicates substantial moisture availability and stronger interaction. • Negative ACI in some instances signify less water vapour presence. [ABSTRACT FROM AUTHOR]

Abstract A simultaneous observation of the water-soluble organic nitrogen (WSON) in the gaseous and particulate phases was conducted at a forested site in Japan for two years to clarify the generation mechanism and possible sources of the gaseous and particulate WSON. The concentration of the WSON in the aerosols was 0.070 μg m−3 on average, ranging from the concentration below the detection limit (DL) to 0.302 μg m−3. A large portion (about 73%) of the particulate WSON was distributed in the fine-mode range (d < 2.0 μm). The concentration of the gaseous WSON was 0.041 μg m−3 on average, ranging from the concentration below the DL to 0.195 μg m−3. About 37% of the atmospheric WSON was distributed in the gas phase, and about 59% of the gaseous WSON was basic. The coarse-mode (d = 2.0–10 μm) WSON showed an unclear seasonal trend, but increased in the summer. Its concentration showed a significant correlation only with the WSOC concentration among the measured species in the coarse aerosols. Suspended organic materials from primary sources, such as plant debris, would be a possible source for the coarse-mode WSON. The WSON in the fine-mode range showed a clear seasonality with enhanced concentrations from the spring to summer. The fine-mode WSON concentration showed a strong correlation with the acidity of the fine particles and the concentration of the gaseous basic WSON, suggesting the secondary production of the WSON in the acid fine particles from the gaseous basic WSON. The basic WSON in the gas phase showed a similar seasonal trend with the gaseous ammonia and strongly correlated with the temperature, which suggests the temperature dependent-volatilization of the gaseous basic WSON species from terrestrial vegetation and/or soil. The seasonal trend of the gaseous acid WSON was unclear, and its concentration did not show significant correlations with any parameters. The possible source and chemical forms of the gaseous acid WSON cannot be deduced at the present time. Highlights • About 73% of the WSON in the aerosols was distributed in the fine-mode range. • About 59% of the gaseous WSON was basic species. • Possible source of the coarse-mode WSON is primary emissions, such as plant debris. • Secondary production from the gaseous basic WSON is the source of the fine-mode WSON. • The gaseous basic WSON would be derived from the terrestrial vegetation and/or soil. [ABSTRACT FROM AUTHOR]

Abstract Previous studies exploring the impact of precursor emissions and meteorological variables on PM 2.5 concentrations were typically conducted over a short period and in urban environments. In this analysis, near-surface sulfate and nitrate mass concentrations at a 10-km resolution over the North China Plain (NCP) from 2006 to 2014 were first obtained based on satellite aerosol optical depth (AOD) data and the global 3D chemical transport model (GEOS-Chem) in combination with vertical profiles from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). Using ground-based PM 2.5 component concentrations, our satellite-based model yielded correlation coefficients (r) of 0.72 for sulfate and 0.70 for nitrate. Second, the spatiotemporal patterns of the chemical composition and corresponding precursor gases collected from the Ozone Monitoring Instrument (OMI) during the study period were analyzed. The highest levels of nitrate (∼30 μg/m3) and sulfate (∼25 μg/m3) were concentrated in Hebei, Shandong, Henan and Beijing, and the monthly variations of nitrate and NO 2 presented a strong correlation coefficient (0.67). Inter-annual changes of nitrate and NO 2 exhibited increasing trends of 1.43%/yr and 1.60%/yr, respectively. In contrast, sulfate and SO 2 decreased at rates of 3.5%/yr and 0.76%/yr, respectively, and presented a negative correlation (−0.54). Third, the relationships between the components or precursor gases and relative humidity (RH), planetary boundary layer height (PBLH), temperature (TEM) and wind speed (WS) were compared. The results showed that high levels of NO 2 were usually accompanied by stable atmospheric conditions (i.e., low TEM, shallow PBLH, low RH and mild WS). Moreover, the nitrate concentration was often dependent on NO 2 , and they showed similar characteristics with meteorological factors. PBLH and WS had the greatest influence on nitrate concentrations, whereas the effects of RH and WS varied seasonally. Under beneficial conditions, i.e., high TEM, RH and PBLH and low WS, SO 2 rapidly converted to sulfate and fluctuated inversely with the sulfate concentration. Overall, high nitrate levels were primarily associated with anthropogenic causes (i.e., extensive emissions), whereas meteorological conditions have a greater effect on the formation of sulfate concentrations than emissions. Highlights • Our satellite-based model yielded a correlation coefficient (r) of 0.72 for sulfate and 0.70 for nitrate. • A strong correlation coefficient of 0.67 was found between monthly variations of nitrate vs. OMI_NO 2. • Sulfate and SO 2 decreased at rates of 3.5%/yr and 0.76%/yr, respectively, and presented a negative correlation (−0.54). • High nitrate levels were mainly associated with anthropogenic extensive emissions. • Meteorological conditions have a greater effect than emissions on sulfate concentrations. [ABSTRACT FROM AUTHOR]

Abstract Studies including multiple isotope systems in aerosols promises unparalleled insights into sources and pathways of metals in the atmosphere. However, such studies remain rare because of the challenges associated with small sample sizes and low analyte masses of the target elements. Here, we present the first study combining accurate and precise determination of Pb, Cu and Zn isotopic ratios in aerosols and anthropogenic materials collected in São Paulo, Brazil. We use a sequential ion chromatography procedure with two different resins for the separation and purification of the analytes. Multi collector mass spectrometry is used for the accurate and precise determination of the isotope ratios. Long term analytical reproducibilities are ±0.035 for 206Pb/204Pb, ± 0.13‰ for δ65Cu NIST and ±0.1‰ for δ66Zn JMC (±2σ). Accuracy is assessed using certified reference materials (CRM NIST 2783 aerossol, BRP-1 and others). We analyzed 57 source samples (road dust, tires, cement, road tunnel aerosol) and 113 aerosol samples collected between 2013 and 2015. The results for São Paulo are critically compared with previously published data from studies conducted in São Paulo, London and Barcelona. The key findings are: 1. The isotope signatures for Zn in tires (δ66Zn JMC = 0.16 ± 0.14, 2σ, n = 9) and road dust (δ66Zn JMC = 0.17 ± 0.19, 2σ, n = 13) are similar in São Paulo and London suggesting that this isotope system can be used as element specific tracers for non-exhaust traffic. 2. 206Pb/207Pb vs δ66Zn JMC and δ66Zn JMC vs δ65Cu NIST multi-isotopic diagrams successfully separate wear off from cars including tires and brakes, car exhaust, industrial emissions and cement sources and improves the discrimination of air pollutant sources. 3. The source identification based on isotope ratios agrees source apportionment based on emissions inventory from these cities. 4. We present Pb, Cu and Zn isotopic data for the first time for the CRM NIST 2783 and BRP-1. These new data will enable future intercalibration and quality controls in other laboratories. Our study confirms that stable isotope ratio analysis have a great potential for element specific source characterization (e.g., separating non combustion traffic sources from combustion sources) for Cu, Zn and Pb. Graphical abstract Image 1 Highlights • Accurate and precise procedure for combined determination of Pb, Cu and Zn isotopic compositions in environmental samples. • Characterization and discrimination of pollutant sources in the atmosphere using isotopic compositions of Pb, Cu and Zn. • Element specific universal isotopic signatures for non-exhaust vehicular traffic. • Source identification based on isotopic signatures is in line with emissions inventory from São Paulo, London and Barcelona. [ABSTRACT FROM AUTHOR]

Abstract A number of laboratory experimental investigations, field campaigns, and modeling results have emphasized the role of aqueous-phase photochemical reactions in the formation of secondary organic aerosols (SOA). However, investigations focused on aqueous-phase reactions under high ionic-strength conditions are scarce. Here we study the photochemical behavior of a lignin-derived compound, acetosyringone (AcS), upon addition of an inert salt (NaClO 4). The increase in the ionic strength modifies the acidic constant of AcS, enhancing its deprotonation. As a consequence, the UV-VIS absorption spectra of AcS undergo modifications due to red shifts at high ionic strength of the electronic transitions n → π* (from λ max = 297 nm to λ max = 354 nm) and π → π* (from λ max = 214 nm to λ max = 247 nm). At fixed pH = 4, representative of moderately acidic atmospheric aerosol deliquescent particles, the pseudo-first-order rate constants (k 1st) of AcS increased by ∼6 times from a dilute aqueous phase to a solution with an effective ionic strength I eff. = 0.46 M. The rate constant then followed a saturation trend at elevated ionic strength up to I eff. = 3.1 M. A similar saturation effect of the observed rate constants with ionic strength was observed in presence of NaCl and Na 2 SO 4. Differential absorption spectroscopy (DAS) methodology was applied to examine the changes in absorption spectra of AcS upon prolonged light irradiation. The very subtle pH-induced changes of the absorption spectra of irradiated AcS are due to the formation of acidic compounds emerged upon photochemical transformation of AcS. Highlights • The increase of ionic strength leads to a red shift of n→π* absorption band of AcS. • The pKa of AcS, hence acidity is affected with increasing ionic strength. • The decay rate of AcS increases by 6 times from I = 0 M to I = 0.5 M. • Photochemical evolution of AcS leads to acidification of the aerosol particles. [ABSTRACT FROM AUTHOR]

Abstract Surrogate surfaces are used to measure atmospheric dry deposition of contaminants and are sometimes designed intentionally with simple geometry to estimate the lower limit of the flux to any surface. However, most surrogate surfaces have a small collection area: long periods of dry weather may be needed to obtain sufficient deposited contaminants to be detected and quantified, and such exposure periods may not be common in wet climates. In this study, two relatively large surrogate surfaces—disks with surface areas >1 m2—were designed to measure dry deposition of F−, Cl−, SO 4 2−, and NO 3 − in Syracuse, NY. Results indicate that good reproducibility is possible for measurements with exposure periods of 2–6 days. The ranges of dry deposition velocities for each species are as follows: F− (0.6–2.5 cm/s), Cl− (1.9–9.2 cm/s), SO 4 2− (0.11–1.8 cm/s), and NO 3 − (0.1–1.1 cm/s). Fluxes were also measured to four separate sections of the disk; results suggest that deposition varies somewhat across the disk in a way that is consistent with boundary layer thickness predicted by Computational Fluid Dynamics modeling. Graphical abstract Image 1 Highlights • Two large disks measured dry deposition of atmospheric anions for short dry periods. • Dry deposition velocities were obtained for F−, Cl−, SO 4 2−, and NO 3 −. • Winter deposition of Cl− and SO 4 2− substantially exceeded summer and fall deposition. • Fluxes were measured to sections of the disks to check uniformity in deposition. • Fluxes measured to different sections of the disks varied, but not greatly. [ABSTRACT FROM AUTHOR]

Abstract Aerosol and cloud condensate nuclei (CCN) measurements in the area of Athens during HyGRA-CD campaign (May–June 2014) identified a significant diversity in particle properties. In this study we select two distinct cases in terms of meteorology and air mass origin in order to analyze the transport mechanisms inside the Planetary Boundary Layer (PBL) and in the free troposphere and discuss the possible contribution of aerosol in cloud formation. The detection of aerosol layers was based on the lidar technique using multi-wavelength detection schemes. The first case is characterized by a double dust layer arriving over Athens with a shallow and younger plume centered at about 1.8 km and a deeper and more aged plume centered at 3.4 km. These layers originate from different sources and follow different transport paths in the atmosphere which explains also their different optical/geometrical properties. The second case is typical of frontal activity and low cloud formation during daytime. Low level convergence of maritime and continental air masses enhances the updraft velocities inside Athens basin and results in CCN activation and cloud formation along the frontal line. Highlights • Aged and fresh dust coexists with marine and local anthropogenic emissions. • First study to examine CCN activation over Athens using detailed modeling and observations. • Vertical wind component is the main driving factor for the formation of clouds. • Aerosol properties affect CCN activation and cloud condensates size and numbers. [ABSTRACT FROM AUTHOR]

As one of the important sources of aerosols, new particle formation events can affect the spatiotemporal distribution of CCN. To analyze the characteristics of new particle formation (NPF) events and their effects on cloud condensation nuclei (CCN) during the summer at Mt.Tian, the data of aerosol size distribution and CCN number concentrations were measured using an aerosol wide-range particle size spectrometer and a cloud condensation nuclei counter from August 4 to 25, 2019, and combined with meteorological data and polycyclic aromatic hydrocarbons (PAHs) data. NPF events at Mt.Tian occurred seven days during the observation period, accounting for 32% of the observation days, and usually occurred at 13:00 and ended at 17:00 (Beijing Time, same below). NPF events particularly influenced the diurnal variations of aerosol number concentrations in different modes. The number concentrations of nucleation and Aitken modes increased rapidly while the accumulation mode increased slowly during 13:00 and 17:00 on NPF days. The peak particle number concentrations in the nucleation, Aitken and accumulation modes on NPF days were 5360.1 cm−3, 7185.6 cm−3 and 839.3 cm−3, respectively, which were 3.3, 1.8 and 1.7 times higher than those on non-NPF days during 13:00 and 17:00. The meteorological conditions of temperature higher than 20 °C, air pressure lower than 806 hPa, relative humidity (RH) lower than 40% and wind speed higher than 2.2 m s−1 are favorable for the occurrence of NPF events. The NPF events at Mt.Tian can impact the mass concentration of PAHs. More Fluoride (FL) and Phenanthrene (PHE) were generated on NPF days. The mass concentrations of FL and PHE on NPF days were 0.002 ± 0.003 ng m−3 and 0.020 ± 0.010 ng m−3, which were 243.54% and 28.44% higher than those on non-NPF days, respectively. NPF events were conducive to increased CCN concentration at Mt.Tian. After the NPF events, the mean number concentrations of CCN at each supersaturation (SS) on NPF days was about 20%–50% higher than on non-NPF days. The contribution of NPF events to the CCN number concentrations was 35.75%, 28.56%, 44.15%, 42.11% and 29.12% at 0.1%, 0.2%, 0.4%, 0.6% and 0.8% SS, respectively. • Favorable meteorological conditions for NPF events at Mt.Tian were analyzed. • NPF events significantly affect the mass concentrations of FL and PHE compared with other PAHs. • The NPF events enhanced CCN population significantly at Mt.Tian. [ABSTRACT FROM AUTHOR]

Wind-dispersed pollen grains emitted from vegetation are directly injected into the atmosphere being an important source of natural aerosols globally. These coarse particles of pollen can rupture into smaller particles, known as subpollen particles (SPPs), that may act as cloud condensation nuclei (CCN) and affect the climate. In this study, we characterize and investigate the ability of SPPs of 10 Mediterranean-climate pollen types to activate as CCN. A continuous flow CCN counter (CCNC) was used to measure the activation of size-selected (80, 100 and 200 nm dry mobility diameter) particles at different supersaturations (SS). Hygroscopicity parameter (κ) for each SPP type and size has been calculated using κ-Köhler theory. Organic chemical speciation and protein content has been determined to further characterize pollen solutions. Furthermore, the surface activity of SPPs has also been investigated by using pendant drop tensiometry. All studied SPP samples show critical supersaturation (SS Crit) values that are atmospherically relevant SS conditions. Hygroscopicity κ values are in the range characteristic of organic compounds (0.1–0.3). We found that organic speciation and protein content vary substantially among pollen types, with saccharides and fatty acids being the only organic compounds found in all pollen types. A clear relationship between SPP activation and its organic composition was not observed. This study also reveals that all SPPs investigated reduce the surface tension of water at high concentrations but at diluted concentrations (such as those of activation in the CCNC), the water surface tension value is a good approximation in Köhler theory. Overall, this analysis points out that pollen particles might be an important source of CCN in the atmosphere and should be considered in aerosol-cloud interactions processes. [Display omitted] • Subpollen particles (SPPs) show κ values in the 0.1–0.3 range. • SPPs activate as CCN at atmospheric supersaturation conditions. • Saccharides and fatty acids are organic compounds found in all pollen types. • The droplet surface tension reduction is observed at high concentration of SPPs. • Reduction of surface tension does not show a relevant effect on SPP activation. [ABSTRACT FROM AUTHOR]

Atmospheric lead pollution has adverse health effects on humans. Identification of anthropogenic Pb sources is thus crucial for understanding of pollution-related risks and for formulation of efficient abatement strategies. We analyzed concentrations and isotope ratios of Pb in fine air-borne particulate matter (PM 2.5) in three Central European cities. Aerosol sampling in 12-h intervals was performed during summer and winter in Hradec Králové, Olomouc and Brno, regional centers of highly industrialized Czech Republic, each with a population of more than 90 thousand. Lead analysis was complemented with concentration measurements of Zn, Cu, Cd, As, Sb, and S. Trace element and PM 2.5 concentrations were higher in winter than in summer in all studied cities, on average by 47%. The overall mean concentration of PM 2.5 in urban air was 21 μg m−3, similar to that in Bern (Switzerland) and Vienna (Austria). Across the sites, 206Pb/207Pb ratios ranged from 1.142 to 1.178 in summer and from 1.143 to 1.173 in winter. The mean 206Pb/207Pb ratios were statistically indistinguishable in all three studied cities (1.165 in Hradec Králové, 1.163 in Olomouc, and 1.160 in Brno). In the 206Pb/207Pb vs. 208Pb/207Pb graph, Pb isotope composition of summer samples formed a straight line, whereas Pb isotope composition of winter samples was shifted toward higher 208Pb/207Pb ratios. A Pb isotope inventory of regional pollution sources indicated that winter-time Pb pollution was not caused solely by household heating and increased electricity production in coal-burning power plants. Recycling of industrial Pb originating from Variscan ores and waste incineration could have shifted the 208Pb/207Pb ratio of PM 2.5 to higher values, however, such sources do not emit more Pb in winter than in summer. Remobilization of legacy alkyl-Pb from gasoline additives and Pb emissions from current unleaded gasoline and diesel could have shifted both Pb isotope ratios to lower values. [Display omitted] • Trace element concentrations in urban atmosphere were 50% higher in winter. • Isotope compositions of air-borne Pb in summer and winter were strikingly different. • Combustion of Polish coal in households contributed to Pb isotope ratios in PM 2.5 • Waste incineration may have shifted the 208Pb/207Pb ratio of PM 2.5 to higher values. • Mobilization of legacy alkyl-Pb from gasoline could affected some Pb isotope ratios. [ABSTRACT FROM AUTHOR]

We looked into the long-term variability of aerosols and clouds over Eastern China (EC) using MICAPS ground-based data from 1995 to 2019 and MODIS aerosol optical depth (AOD) retrieval from 2003 to 2019. The ground-based observed visibility (VIS) was used to characterize aerosol concentrations. Our study indicate that VIS shows a significant shift over EC in recent decades, as evidenced by falling (P1: 1995–2006)-flat (P2: 2007–2013)-rising (P3: 2014–2019) periods. Correspondingly, a change was observed in cloud fraction (CF) from a strong increase to a slow fluctuation during the three periods over the Beijing-Tianjin-Hebei (BTH), but no significant variation over the Yangtze River Delta (YRD) region. In addition, the CF-VIS shows a negative correlation during both P1 and P3 periods while this relationship weakened during P3 (35% weaker in BTH and 44% weaker in YRD). However, it is important to note that this weakening may be influenced by a few factors, such as data processing methods, the location of aerosols relative to the cloud, relative humidity (RH), and large-scale circulation etc. Further studies, including numerical simulations and analysis, are required to determine how much change of cloudiness is attributed to aerosols. • Cloud fraction (CF) has changed from strong to slow growth during the rising and declining aerosol periods1995–2019) over BTH. • Aerosol concentrations, characterized by visibility (VIS), have been negatively correlated with CF during the study period. • The negative correlation between VIS and CF has weakened during the declining period of aerosol emissions in recent years. [ABSTRACT FROM AUTHOR]

Temporal variation in cloud cover and surface conditions greatly affects estimation errors associated with reference surface reflectance and atmospheric composition retrievals. In this study, to determine an optimal temporal window for clear-sky composition methods that are used to identify surface reflectance for the retrieval of atmospheric properties, we analyzed temporal variation in surface reflectance and cloud fractions using long-term daily observations from the Moderate Resolution Imaing Spectroradiometer (MODIS) satellite. For the temporal variation in surface reflectance, gridded pixels with a standard deviation less than 0.025 represented 87.0%, 84.5%, 80.5%, and 77.3% of the total pixels for periods of 15, 20, 30, and 40 days, respectively. The temporal variability of surface reflectance was lowest in summer and highest in winter due to vegetation and snow cover changes over land surface in East Asia. For the temporal variation in cloud fractions, pixels with a cloud fraction <10% ranged from 91.2% (15-day) to 98.1% (40-day). Only temporal windows of 30 and 40 days satisfied the criterion of 95% cumulative distribution in the 10% cloud fraction range. Thus, and appropriate temporal window for clear-sky composition methods must be selected in consideration of the seasonal dependency of surface types and cloud cover variation. The temporal window for the clear-sky composition must be longer than 30 days considering the temporal variability of cloud cover, and shorter than 30 days considering that of surface reflectance. However, seasonal dependencies of surface reflectance and cloud fraction are also additionally considered to select the appropriated temporal window for the clear-sky composition. • Analysis of temporal variation in surface reflectance and cloud fraction using daily satellite observation. • Seasonal and regional dependence for temporal variability of surface reflectance due to vegetation and snow cover change. • Identify an optimized temporal window for the clear-sky composition by considering surface reflectance and cloud fraction. [ABSTRACT FROM AUTHOR]

Per- and polyfluoroalkyl substances (PFASs), also known as "forever chemicals" received significant attention during recent years due to their environmental persistence and emerging evidence on their toxicity to humans. In this work we present the first measurements of PFASs in inhalable fraction of airborne particles PM 2.5 (particulate matter that has a diameter ≤2.5 μm) in Brazil collected during Covid restriction period. Three PFASs that included perfluorooctanesulfonic acid (PFOS), a restricted by Stockholm convention perfluorooctanoic acid (PFOA), and 6:2 fluorotelomer sulfonate (6:2 FTS) were detected at concentrations up to 0.3 pg/m3. These values do not include uncertainties associated with potential adsorption of gas phase PFASs on the filters but may be lower than those generally occurring at Curitiba, Brazil due to an abrupt reduction in industrial activities and a major decrease in the use of transport during Covid lockdown. Although current air quality regulations do not set inhalable limits for PFASs, there is a concern that these substances can accumulate in human body. The detection of 6:2 FTS in PM 2.5 samples is a cause for concern due to its persistence in the atmosphere and emerging evidence that FTS could have health effects comparable with those of PFOA and PFOS. Multiple pollution sources of PFAS in Curitiba were considered based on airmass trajectories and wind roses. Our results raise the question of whether the observed PFOS in Curitiba is linked to sulfluramid, a pesticide that is permitted for use in Brazil. • First observation of PFASs i.e., PFOS, PFOA in PM 2.5 and 6:2 FTS in PM in Brazil. • Identified PFASs included those restricted by Stockholm convention. • PFASs found in PM 2.5 at low levels, but can accumulate in human tissues over time. • PFASs were observed during Covid when most of the industrial activities were reduced. • Research needed to confirm links between observed PFOS and pesticide-treated plantations. [ABSTRACT FROM AUTHOR]

Abstract Aerosol chemistry measurements were performed during the routine monitoring periods in the urban atmosphere of Gwangju, Korea. Routine aerosol monitoring was carried out every sixth day in order to investigate the dependence of domestic sources and air mass transport characteristics on physicochemical and optical properties of atmospheric aerosol. Aerosol optical properties; atmospheric extinction and scattering coefficients were also measured continuously with a transmissometer and a nephelometer, respectively in order to investigate the causes of visibility impairment. Prevailing atmospheric condition was classified into four categories; one affected by stagnant condition (D), one affected by continental and domestic aerosols (CD), one affected by marine and domestic aerosols (MD), and one affected by continental, marine and domestic aerosols (CMD). Atmospheric condition type was further classified into thirteen sub-categories with the occurrences of episodic events such as Asian dust storm, biomass burning, and airborne pollen. The air mass types of D, CD, MD, and CMD were observed to be 11, 18, 43, and 78 events out of total 150 events, respectively. The fine mass concentration increased under continental air mass types. The average fine mass concentration of 23.0 ± 8.6 μg m−3 for CD type was slightly larger than that of 20.7 ± 5.2 μg m−3 for CMD type. Both of them were higher than that for D (18.9 ± 4.5 μg m−3) type. Increments of the fine mass concentrations for Asian dust storm (A) and Biomass-burning (B) events ranged from 141 to 151% and from 152 to 160% compared to those for D and CD types, respectively. The increments in the mass concentrations of nitrate, OC, EC, and BC for CD and CMD types in comparison with D air mass type were calculated to be approximately 17, 6, 8, and 22%, respectively. The mean mass extinction efficiency of PM 10 was relatively higher in D (3.6 ± 1.6 m2 g−1) type and B events (4.1 ± 1.5 m2 g−1), but it was the lowest in MD air mass type. The aerosols observed in Gwangju were found to be influenced by the continental aerosol during the A events. Aerosol of CMD air mass type caused mainly poor visibility. The visibility reduction of Gwangju was influenced by the increase of carbonaceous particles under both domestically stagnant condition and air mass pathway from the continent. And ammonium sulfates and ammonium nitrates contributed the largest in CMD air mass type. Highlights • The fine mass concentration increased under continental air mass types. • The biomass-burning events were mainly attributed to domestic aerosols. • The contributions of NHSO, NHNO, and OMC increased as visibility became poor. • Haze was dominantly influenced by visibility-impairing aerosol rather than RH. [ABSTRACT FROM AUTHOR]

Abstract As part of the Observations and Modeling of the Green Ocean Amazon (GoAmazon 2014/5) Experiment, detailed aerosol and trace gas measurements were conducted near Manaus, a metropolis located in the central Amazon Basin. Measurements of aerosol particles and trace gases were done downwind Manaus at the sites T2 (Tiwa Hotel) and T3 (Manacapuru), at a distance of 8 and 70 km from Manaus, respectively. Based on in-plume measurements closer to Manaus (site T2), the chemical signatures of city emissions were used to improve the interpretation of pollutant levels at the T3 site. We derived chemical and physical properties for the city's atmospheric emission ensemble, taking into account only air masses impacted by the Manaus plume at both sites, during the wet and dry season Intensive Operating Periods (IOPs). At T2, average concentrations of aerosol number (CN), CO and SO 2 were 5500 cm−3 (between 10 and 490 nm), 145 ppb and 0.60 ppb, respectively, with a typical ratio ΔCN/ΔCO of 60–130 particles cm−3 ppb−1. The aerosol scattering (at RH < 60%) and absorption at 637 nm at T2 ranged from 10 to 50 M m−1 and 5–10 M m−1, respectively, leading to a mean single scattering albedo (SSA) of 0.70. In addition to identifying periods dominated by Manaus emissions at both T2 and T3, the plume transport between the two sampling sites was studied using back trajectory calculations. Results show that the presence of the Manaus plume at site T3 was important mainly during the daytime and at the end of the afternoons. During time periods directly impacted by Manaus emissions, an average aerosol number concentration of 3200 cm−3 was measured at T3. Analysis of plume evolution between T2 and T3 indicates a transport time of 4–5 h. Changes of submicron organic and sulfate aerosols ratios relative to CO (ΔOA/ΔCO and ΔSO 4 /ΔCO, respectively) indicate significant production of secondary organic aerosol (SOA), corresponding to a 40% mass increase in OA and a 30% in SO 4 mass concentration. Similarly, during air mass arrival at T3 the SSA increased to 0.83 from 0.70 at T2, mainly associated with an increase in organic aerosol concentration. Aerosol particle size distributions show a strong decrease in the Aitken nuclei mode (10–100 nm) during the transport from T2 to T3, in particular above 30 nm, as a result of efficient coagulation processes into larger particles. A decrease of 30% in the particle number concentration and an increase of about 50 nm in geometric mean diameter were observed from T2 to T3 sites. The study of the evolution of aerosol properties downwind of the city of Manaus improves our understanding of how coupling of anthropogenic and biogenic sources may be impacting the sensitive Amazonian atmosphere. Graphical abstract Image 1 Highlights • Manaus emissions significantly impacts Amazonian aerosols properties. • Organic aerosols increase 40% in mass downwind of Manaus, attributed to secondary formation. • Sulfate aerosols increase 30% in mass downwind of Manaus, attributed to SO 2 oxidation. • Aerosol mean diameter increases about 60 nm during plume evolution, in the dry season. [ABSTRACT FROM AUTHOR]

Abstract Model of aerosols and cloud formation processes requires extensive data on hygroscopic properties of water soluble organic species at lower troposphere relevant temperatures, which are ubiquitously found in atmospheric aerosols. Recent field studies (Kerminen et al., 1998) have revealed that sea salt aerosols can be efficiently chemically processed by water soluble carboxylic acids and lead to chloride depletion and formation of carboxylic acid salts. In this study, we report hygroscopic properties of four carboxylic acid salts, namely, sodium formate, sodium acetate, sodium oxalate and sodium succinate at temperatures commonly encountered in the lower troposphere ranging from 295.8 K to 270.0 K for the first time via attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of these carboxylic salts as a function of temperature were derived using both changes in water-to-solute (WSR) data and changes in band positions and shapes of carboxylate asymmetric and symmetric stretch modes. Hygroscopic data were also fitted by polynomial and corresponding coefficients were obtained. Our results have shown that these carboxylic acid salts exhibit strong temperature dependence and they would deliquesce at a lower humidity and are more likely to remain deliquesced when they are elevated in the troposphere. Since all these carboxylic acid salts present very different hygroscopic behaviors at lower temperatures from that of NaCl, chemically processed sea salt aerosols by carboxylic acids are expected to have fairly different phase state, size, and water content, consequently affecting their reactivity, lifetime, and ability to serve as cloud condensation nuclei. Highlights • Temperature dependent hygroscopic behaviors of carboxylic acid salts are reported. • Hygroscopicity data are fitted by polynomial and coefficients are obtained. • Carboxylic acid salts exhibit different hygroscopic behaviors from that of NaCl. • Results offer new insight into sea salt aerosols and their roles in climate system. [ABSTRACT FROM AUTHOR]

Abstract Total and size-resolved concentrations and emission factors are used to compare fleet-averaged vehicle emissions in Pittsburgh, PA in 2002 and 2014. Winter-time traffic tunnel measurements acquired using dual scanning mobility particle sizers (SMPS) over the size range 3–500 nm form the key input for the analysis. Size-resolved mass emission factors were calculated assuming a nanoparticle aggregate model. The ultrafine particle (<30 nm) emissions of diesel vehicles significantly dropped from 2002 to 2014. In the 2014 study, a thermodenuder (TD) was deployed together with the SMPS to measure emissions of non-volatile particles. After evaporation at 250 °C inside the TD, the median diameter of the number-size distribution shifted from 16 nm to ∼7 nm. The total particle number decreased significantly (69%) after evaporating inside the TD, indicating that vehicle emitted particles may be largely externally mixed and that a large fraction of these particles may be purely composed of volatile components. Based on the SMPS-TD measurements, we report a size-resolved volatile-to-non-volatile-component-ratio for vehicle emitted particles. It shows that smaller particles (10–60 nm) emitted by vehicles are dominantly (over 75%) composed of volatile components. We also apportioned the size-resolved particles and non-volatile particle mass and number emission factors for both gasoline and diesel vehicles. Diesel vehicles emitted significantly more ultrafine particles and non-volatile particles than gasoline vehicles. Graphical abstract Image 1 Highlights • Size-resolved particle emission factors for on-road vehicles show that particles are largely externally mixed. • Particles smaller than 50 nm are dominated by volatile components. • Emissions from gasoline and diesel vehicles have been reduced since 2002, with larger reductions in diesel emissions. [ABSTRACT FROM AUTHOR]

Particle number size distribution in a suburban Beijing was measured during the HOPE-J3A (Haze Observation Project Especially for Jing–Jin–Ji Area) field campaigns in 2015 from 18 June to 23 July (summer) and 2 to 25 December (winter). Average particle concentrations during the summer and winter campaigns were 9.6 ± 4.8 × 10 3 cm −3 and 13.9 ± 8.3 × 10 3 cm −3 , respectively. Particle numbers were dominated by Aitken mode particles in both seasons. During the winter campaign, pollution events occurred every four to five days, each lasting for two to three days. In contrast, pollution events lasted for one to two days every six to seven days during the summer campaign. Aitken mode particles were 50% higher in the winter but new particle formation (NPF) events occurred more frequently in the summer. NPF events usually starts at around 10:00 LT (local time) in the summer but 12:00 LT in the winter. Aitken and accumulation mode particles accounted for 43.5% and 38.2% of all particles. The proportion of Aitken mode to total particles remained almost the same during summer, while it increased as haze intensified in winter. Particle number concentration was closely correlated with traffic and residents living activities and wind speed, with higher concentrations during rush hours, heating period and in the southerly wind. These results, when combined with trajectory cluster analysis, suggest that Aitken and accumulation mode particles were mainly from regional transport during the summer campaign, but from vehicle and coal-combustion emissions during the winter campaign. [ABSTRACT FROM AUTHOR]

Aerosol and water vapor radiative forcings, shortwave atmospheric heating rates and longwave atmospheric cooling rates were determined based on in situ physical and chemical measurements of aerosol, associated with the Mie theory and a radiative transfer model, LOWTRAN7, during the two haze episodes in the winter of 2013 in Tianjin, China. The aerosol types considered in LOWTRAN7 included rural, urban, marine, desert and custom aerosols. The default ratio of the absorption coefficient to the extinction coefficient for urban aerosol in LOWTRAN7 was approximately double of those found in this work, implying the weaker absorption ability of aerosols in the North China Plain (NCP). Moreover, the aerosol is assumed to be evenly distributed below 1 km of planetary boundary layer (PBL) on hazy days in LOWTRAN7. If the default urban aerosol optical properties and extinction profile in LOWTRAN7 is employed directly, a larger energy imbalance between the atmosphere and surface is generated and the warming effect of the aerosol is magnified. Hence, modified urban aerosol optical properties were established to replace the corresponding parameters’ database in LOWTRAN7. The aerosol extinction profiles were obtained based on a 255-m meteorological tower and observed results from the studies about Tianjin. In the NCP, the aerosol had little impact on atmospheric counter radiation. The water vapor is the crucial factor that affects atmospheric counter radiation. Both modified high shortwave heating rates and longwave cooling rates occur near the surface due to the abundance of aerosol and water vapor. The modified net atmospheric heating rate near the surface is 1.2 K d −1 on hazy days and 0.3 K d −1 on non-hazy days. Compared with the default urban aerosol optical properties and its vertical distribution in LOWTRAN7, the feedback effect of the modified urban aerosol on the boundary layer may not necessarily result in a stable lower atmosphere, but depends on the aerosol light absorption ability and its vertical distribution. [ABSTRACT FROM AUTHOR]

Oxidation products of α-pinene represent a fraction of organic matter in the environmental aerosol. α-pinene is one of most abundant monoterpenes released in the atmosphere by plants, located typically in boreal, temperate and tropical forests. This primary compound reacts with atmospheric oxidants, such as O 3 , O 2 , OH radicals and NO x , through the major tropospheric degradation pathway for many monoterpenes under typical atmospheric condition. Although several studies identified a series of by-products deriving from the α-pinene photo-oxidation in the atmosphere, such as pinic and cis-pinonic acid, the knowledge of the mechanism of this process is partially still lacking. Thus, the investigation of the distribution of these acids in the different size aerosol particles provides additional information on this regard. The aim of this study is twofold. First, we aim to improve the existing analytical methods for the determination of pinic and cis-pinonic acid in aerosol samples, especially in terms of analytical sensitivity and limits of detection (LOD) and quantification (LOQ). We even attempted to increase the knowledge of the α-pinene photo-oxidation processes by analysing, for the first time, the particle-size distribution up to nanoparticle level of pinic and cis-pinonic acid. The analysis of aerosol samples was carried out via high-performance liquid chromatography coupled to a triple quadrupole mass spectrometer. The instrumental LOD values of cis-pinonic and pinic acid are 1.6 and 1.2 ng L −1 while LOQ values are 5.4 and 4.1 ng L −1 , respectively. Samples were collected by MOUDI II™ cascade impactor with twelve cut-sizes, from March to May 2016 in the urban area of Mestre-Venice (Italy). The range concentrations in the aerosol samples were from 0.1 to 0.9 ng m −3 for cis-pinonic acid and from 0.1 to 0.8 ng m −3 for pinic acid. [ABSTRACT FROM AUTHOR]

Aerosols have adverse effects on human health and air quality, changing Earth's energy balance and lead to climate change. The components of aerosol are important because of the different spectral characteristics. Based on the low hygroscopic and high scattering properties of organic matter (OM) in fine modal atmospheric aerosols, we develop an inversion algorithm using remote sensing to obtain aerosol components including black carbon (BC), organic matter (OM), ammonium nitrate-like (AN), dust-like (DU) components and aerosol water content (AW). In the algorithm, the microphysical characteristics (i.e. volume distribution and complex refractive index) of particulates are preliminarily separated to fine and coarse modes, and then aerosol components are retrieved using bimodal parameters. We execute the algorithm using remote sensing measurements of sun-sky radiometer at AERONET site (Beijing RADI) in a period from October of 2014 to January of 2015. The results show a reasonable distribution of aerosol components and a good fit for spectral feature calculations. The mean OM mass concentration in atmospheric column is account for 14.93% of the total and 56.34% of dry and fine-mode aerosol, being a fairly good correlation (R = 0.56) with the in situ observations near the surface layer. [ABSTRACT FROM AUTHOR]

In this study, samples of 18 wet precipitations (WPs) and 38 aerosols were collected around a coal-fired power plant (CFPP) located in Xiamen, southeast China, which was equipped with a seawater flue gas desulfurization system. Total particulate mercury (TPM) in aerosol samples, and total mercury (WP-TM), dissolved mercury (WP-DM) and particulate mercury (WP-PM) in WP samples were analyzed for the natural isotopic compositions of mercury. For the first time, both mass dependent fractionation (MDF) and mass independent fractionation of odd (odd-MIF) and even (even-MIF) isotopes of WP-DM and WP-PM were reported and discussed. Both WP-TM and TPM displayed negative MDF and slightly positive even-MIF. Negative odd-MIF was observed in TPM and WP-PM, whereas positive odd-MIF was observed in WP-TM and WP-DM. It was found that the mercury budget in WP-PM samples was mainly controlled by atmospheric particles. Potential sources of mercury in samples were identified via analysis of mercury isotopic signatures and meteorological data with the NOAA HYSPLIT model. The results showed that TPM and WP-PM in solid samples were homologous and the isotopic compositions of WP-TM depended on those of WP-DM. The ratios of Δ 199 Hg/Δ 201 Hg resulting from photochemical reactions and positive Δ 200 Hg values (from -0.06‰ to 0.27‰) in all samples indicated that the mercury coming from local emission of the CFPP together with long-distance transportation were the two main contributing sources. [ABSTRACT FROM AUTHOR]

Satellite and ground based remote sensors provide vital information about aerosol optical and radiative properties. Analysis of aerosol optical and radiative properties during heavy aerosol loading events in Pakistan are limited and, therefore, require in-depth examination. This work examines aerosol properties and radiative forcing during Dust Episodes (DE) and Haze Episodes (HE) between 2010 and 2014 over mega cities of Pakistan (Karachi and Lahore). Episodes having the daily averaged values of Aerosol Optical Depth (AOD) exceeding 1 were selected. DE were associated with high AOD and low Ångström Exponent (AE) over Karachi and Lahore while high AOD and high AE values were associated with HE over Lahore. Aerosol volume size distributions (AVSD) exhibited a bimodal lognormal distribution with a noticeable coarse mode peak at a radius of 2.24 μ m during DE, whereas a fine mode peak was prominent at a radius 0.25 μ m during HE. The results reveal distinct differences between HE and DE for spectral profiles of several parameters including Single Scattering Albedo (SSA), ASYmmetry parameter (ASY), and the real and imaginary components of refractive index (RRI and IRI). The AOD-AE correlation revealed that dust was the dominant aerosol type during DE and that biomass burning and urban/industrial aerosol types were pronounced during HE. Aerosol radiative forcing (ARF) was estimated using the Santa Barbra DISORT Atmospheric Radiative Transfer (SBDART) model. Calculations revealed a negative ARF at the Top Of the Atmosphere (ARF TOA ) and at the Bottom Of the Atmosphere (ARF BOA ), with positive ARF within the Atmosphere (ARF ATM ) during both DE and HE over Karachi and Lahore. Furthermore, estimations of ARF ATM by SBDART were shown to be in good agreement with values derived from AERONET data for DE and HE over Karachi and Lahore. [ABSTRACT FROM AUTHOR]

The differences in PM 2.5 concentrations between two relatively close stations, one situated near a major highway and the other much more distant were used to develop a protocol for determining the impact of highway traffic on particulate matter concentrations at the roadside. The roadside station was <15 m away from the edge of a major highway while the other was located ∼170 m away. The roadside station contains a suite of continuous instrumentation capable of near-real-time speciation of PM 2.5 . The particulate matter difference, formally termed the PM 2.5 imbalance was arbitrarily defined as a case wherein |Near-road PM 2.5 - Far from road PM 2.5 |/Near-road PM 2.5 ≳ 50%. Of interest was the variation of multi-time factors based on ME2 analyses of the speciation data from the roadside station during these imbalance events. Of the 7 mass-contributing ME2 factors, a black carbon factor was determined to be the major cause of the PM 2.5 imbalance and was especially dominant for the case when PM 2.5 concentrations at the roadside station were greater than the farther-station PM 2.5 . The black carbon concentrations observed during these specific events were further regressed against other traffic-related and meteorological parameters with two nonlinear optimization algorithms (generalized reduced gradient and rules ensemble) in our attempts to model any potential relationships. It was observed that the traffic counts of heavy duty vehicles (predominantly diesel-powered) dominated the relationship with black carbon while contributions from light duty vehicles were negligible during these [PM 2.5 ] Roadside > [PM 2.5 ] Farther events at the roadside station. This work details the most critical ways that highway traffic can contribute to local ambient PM 2.5 concentrations that commuters are exposed to and will be important in informing policies and strategies for particulate matter pollution reduction. [ABSTRACT FROM AUTHOR]

Parameterization of the size-resolved particle activation ratio (AR) is useful for the prediction and analysis of the cloud condensation nuclei (CCN) number concentration ( N CCN ). Critical issues for the application of AR parameterizations in models are (1) the consistency of the different parameterization schemes in terms of fitting AR curves and (2) the applicability of the estimate of N CCN under different aerosol conditions. These issues are discussed in this study based on summertime measurements of the size-resolved AR in the North China Plain. By comparing parameterized AR curves, variations in the fitting parameters and application to N CCN calculations, the consistency of the three existing parameterization schemes is confirmed. Based on an analysis using representative AR fitting parameters, the method commonly used to calculate N CCN with a fixed AR was found to be accurate, except during periods affected by strong black carbon (BC) emissions or new particle formation (NPF) events. The N CCN value was overestimated by approximately 10% when BC aerosol emissions were abundant and deviated from the 1:1 line by 15% during NPF events. The bias of the calculated N CCN due to these significant emission or aerosol production events cannot be eliminated by using the appropriate representative fitting parameters. Under these circumstances, accurate prediction of N CCN requires real-time aerosol hygroscopicity data based on CCN measurements. This research furthers our understanding of the relationship between aerosol cloud activation and aerosol spectra. [ABSTRACT FROM AUTHOR]

Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)-derived aerosol vertical profiles were studied in the upper troposphere and lower stratosphere (UTLS) over the Indian summer monsoon (ISM) region during two successive and contrasting monsoon years (2008–2009). An enhanced aerosol layer was observed in the UTLS between 15 and 19 km altitude, in the vicinity of tropopause during both years. However, the optical characteristics of aerosol layers were found to be dissimilar during the two contrasting consecutive summer monsoon seasons. While the depolarization ratio of enhanced aerosol layer (exceeding 0.2) during both years suggested anisotropic nature of particles, the aerosol backscatter coefficient was observed to be more intensified with a sharp peak during the active monsoon year (2008) whereas it was relatively broader with lower magnitude during a drought year (2009). The enhanced backscatter coefficient in the UTLS was found to be closely associated with the variability in tropopause height and convection during both years, which is more pronounced during the active monsoon year as compared to a drought year. Deep convection over the ISM region may inject boundary layer aerosols into the upper troposphere as evidenced from the analysis of the outgoing long-wave radiation (OLR). Our results also showed an enhanced integrated backscatter coefficient (IBC) of about 30%, which is associated with a decrease in OLR of about 7% during the active monsoon year as compared to drought year. These findings were further corroborated using NCEP-NCAR vertical velocity and HYSPLIT air-mass backward trajectory analyses. [ABSTRACT FROM AUTHOR]

The air masses transported from East Asia have a strong impact on the aerosol properties and deposition in the marine boundary layer of the western North Pacific (WNP) during winter and spring. We joined a cruise between 17 Mar. and 22 Apr. 2014 and investigated the changes of aerosol composition and size distribution over the remote WNP and marginal seas. Although the secondary aerosol species (SO 4 2− , NO 3 − and NH 4 + ) in remote WNP were influenced significantly by the continental transport, NH 4 + concentrations were lower than 2.7 μg m −3 in most sampling days and not correlated with non-sea-salt (nss)-SO 4 2- suggesting that the ocean could be a primary source of NH 4 + . Moderate Cl − depletion (23%) was observed in remote WNP, and the inverse relationship between Cl − depletion percentages and nss-K + in aerosols suggested that the transport of biomass burning smoke from East Asia might be a vital extra source of Cl − . Both Asian dust and haze events were encountered during the cruise. Asian dust carried large amounts of crustal elements such as Al and Ti to the WNP, and the dusty Fe deposition may double its background concentration in seawater. Differently, a dramatic increase of dry deposition flux of dissolved particulate inorganic nitrogen was observed during the haze event. Our study reveals that the transport of different continental air masses may have distinct biogeochemical impacts on the WNP by increasing the fluxes of different nutrient elements and potentially changing the nutrient stoichiometry. [ABSTRACT FROM AUTHOR]

Mist events occur frequently worldwide, but the chemical characteristics of the mist droplets has never been investigated because of very low liquid water contents of them. We estimated the concentrations of the mist water, the average concentration of the mist droplets, via the determination of water-soluble components of the coarse aerosol and the observation of the imprints of the droplets on a MgO-coated glass slide. The pH of the mist water was estimated from the equilibrium calculation with the data of the Gran plot of the solution of the dissolved coarse particles, the inorganic ion concentrations of aerosol larger than 10 μm, and the estimated volume of mist water. The mist water was measured as about 1 eq/L total concentration for typical inorganic ions and about pH 4.5 in Yokohama. Such highly concentrated mist droplets may have intense environmental effects. [ABSTRACT FROM AUTHOR]