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This study explores aerosol direct, indirect, and feedback effects on meteorology and fine particulate matter during heat waves of August 2022 over eastern China by using an online coupled regional climate–chemistry–aerosol model. In this period, aerosols exerted mean direct (DRE) and indirect (IRE) radiative effects of −3.9 Wm−2 and −2.4 Wm−2 at TOA, which totally caused a decrease in average surface air temperature by 0.3 °C over east China, accompanied by decreases in PBLH (planetary boundary layer height) and precipitation and an increase in PM2.5 concentration. With the anthropogenic emission reduction from 2013 to 2022, DRE apparently decreased while IRE changed little, leading to a decrease in total aerosol radiative effect (TRE) by 27% at TOA. The weakened TRE resulted in increases in surface air temperature and precipitation by 0.14 °C and 2.7 mm, respectively, on average over east China, with the maximum warming exceeding 0.5 °C in BTH (Beijing–Tianjin–Hebei province). This study highlights a warming trend due to weakened TRE, which may exacerbate heat wave, and an increasing importance of aerosol IRE relative to DRE due to weak sensitivity of cloud properties to aerosol change during the emission reduction. [ABSTRACT FROM AUTHOR]

Aerosols constitute important substance components of the Earth's atmosphere and have a profound influence on climate dynamics, radiative properties, and biogeochemical processes. Here we develop updated emission schemes for dust, sea-salt, and marine primary organic aerosols (MPOA) and augment formation reactions for secondary organic aerosol (SOA) by introducing updated parameterizations within the Community Earth System Model (CESM; version 2.1.3). The modified scheme shifts the original hotspot-like dust emission to a more continuous distribution, improving the dust aerosol optical depth (DAOD) simulations at stations in North Africa and Central Asia. Also, it results in shorter dust residence time, necessary for enhancing concentration simulations downwind of dust source regions. Modifications in the sea-salt emission scheme include an update to sea surface temperature (SST) modulation and the introduction of a relative-humidity-dependent correction factor for sea-salt particle size. The effect of SST is much more significant compared to that of relative humidity. We then extend to incorporate emissions of marine primary organic aerosols (MPOA) as externally mixed with sea-salt aerosols, coupled offline with ocean component Parallel Ocean Program (POP2). The influence of phytoplankton species on modeling MPOA emissions is profound, highlighting the significance of biological diversity in shaping aerosol emissions. In addition to these emission scheme improvements, we also refine the chemical mechanisms in the model. The irreversible aqueous uptake of dicarbonyl compounds is added as a new pathway for the SOA formation in the model. These improvements enrich the capability of the CESM by using ESM's intricate linkage between different spheres of the Earth system, thereby enabling a more comprehensive description of natural aerosol emission and chemical processes and their impacts. [ABSTRACT FROM AUTHOR]

Organic aerosols from marine sources over the western Pacific Ocean of East Asia were investigated using an online coupled regional chemistry–climate model RIEMS-Chem for the entire year 2014. Model evaluation against a wide variety of observations from research cruises and in situ measurements demonstrated a good skill of the model in simulating temporal variation and spatial distribution of particulate matter with aerodynamic diameter less than 2.5 and 10 µm (PM 2.5 and PM 10), black carbon (BC), organic carbon (OC), sodium, and aerosol optical depth (AOD) in the marine atmosphere. The inclusion of marine organic aerosols improved model performance on OC concentration by reducing model biases of up to 20 %. The regional and annual mean near-surface marine organic aerosol (MOA) concentration was estimated to be 0.27 µgm-3 , with the maximum in spring and the minimum in winter, and contributed 26 % of the total organic aerosol concentration on average over the western Pacific. Marine primary organic aerosol (MPOA) accounted for the majority of marine organic aerosol (MOA) mass, and the MPOA concentration exhibited the maximum in autumn and the minimum in summer, whereas marine secondary organic aerosol (MSOA) was approximately 1–2 orders of magnitude lower than MPOA, having a distinct summer maximum and a winter minimum. MOA induced a direct radiative effect (DRE MOA) of - 0.27 Wm-2 and an indirect radiative effect (IRE MOA) of - 0.66 Wm-2 at the top of the atmosphere (TOA) in terms of annual and oceanic average over the western Pacific, with the highest seasonal mean IRE MOA up to - 0.94 Wm-2 in spring. IRE MOA was stronger than, but in a similar magnitude to, the IRE due to sea salt aerosol on average, and it was approximately 9 % of the IRE due to anthropogenic aerosols in terms of annual mean over the western Pacific. This ratio increased to 19 % in the northern parts of the western Pacific in autumn. This study reveals an important role of MOA in perturbing cloud properties and shortwave radiation fluxes in the western Pacific of East Asia. [ABSTRACT FROM AUTHOR]

Organic aerosols from marine sources over the western Pacific Ocean of East Asia were investigated by using an online-coupled regional chemistry-climate model RIEMS-Chem for the entire year 2014. Model evaluation against a wide variety of observations from research cruises and in-situ measurements demonstrated a good skill of the model in simulating temporal variation and spatial distribution of particulate matter with aerodynamic diameter less than 2.5 μm and 10 μm (PM2.5 and PM10), black carbon (BC), organic carbon (OC), sodium, and aerosol optical depth (AOD) in the marine atmosphere. The inclusion of marine organic aerosols apparently improved model performance on OC aerosol concentration. The regional and annual mean near surface marine organic aerosol (MOA) concentration was estimated to be 0.27 μg m-3, with the maximum in spring and the minimum in winter and contributed 26 % of the total organic aerosol concentration on average over the western Pacific. Marine primary organic aerosol (MPOA) accounted for the majority of marine organic aerosol (MOA) mass and exhibited the maximum in autumn and the minimum in summer, whereas marine secondary organic aerosol (MSOA) was approximately 1~2 orders of magnitude lower than MPOA, having a distinct summer maximum and a winter minimum. MOA induced a direct radiative effect (DREMOA) of -0.27 W m-2, and an indirect radiative effect (IREMOA) of -0.66 W m-2 at TOA (IREMOA) in terms of annual and oceanic average over the western Pacific, with the highest seasonal mean IREMOA up to -0.94 W m-2 in spring. IREMOA was stronger than but in a similar magnitude to the IRE due to sea salt aerosol on average, and it was approximately 9 % of the IRE due anthropogenic aerosols in terms of annual mean over the western Pacific, and this ratio increased to 19 % in the northern parts of the western Pacific in autumn. This study reveals an important role of MOA in perturbing cloud properties and shortwave radiation fluxes in the western Pacific of East Asia. [ABSTRACT FROM AUTHOR]

The impacts of vertical distribution of biomass burning (BB) emissions on aerosol distributions and direct radiative effects over the BB source regions of Mainland Southeast Asia (MSEA) and downwind East Asian regions during spring (March to May) 2019 were investigated by applying an online coupled regional chemistry-aerosol-climate model (RIEMS-Chem). Model validation against a variety of observations demonstrated a generally good skill of the model in simulating aerosol chemical components, aerosol optical depth (AOD), and vertical distribution of aerosol extinction coefficient (EXT) when BB emissions were included. Four methods were adopted to represent injection height of BB emissions, including (1) a physical process-based parameterization (BB_param), (2) satellite-based prescribed profiles (BB_prof), (3) temporal-spatial varied injection profiles from the GFAS (Global Fire Assimilation System) dataset (BB_GFAS), and (4) BB emissions released at a fixed altitude (BB_high). The BB_param experiment generally produced better statistics compared to observations. Different BB injection height treatments considerably affected concentrations and distributions of BB aerosols, aerosol optical properties, direct radiative effects of BB aerosols (DRE BB), atmospheric heating rate, and cloud fractions. The simulated sub-regional (100–120°E and 19–26°N, including major BB source and downwind areas) and seasonal mean DRE BB at the top of the atmosphere (TOA) were +1.7 W m−2, +1.3 W m−2, +1.2 W m−2, and +1.7 W m−2 in the BB_param, BB_prof, BB_GFAS, and BB_high experiments, respectively, while the corresponding mean DRE BB at the surface were −30.3 W m−2, -19.1 W m−2, -19.0 W m−2, and -22.1 W m−2. It is noticed that the DRE BB at TOA and at the surface in BB_GFAS were just 68% and 63% of the values in BB_param, and the different injection height treatment had larger influences on DRE BB at the surface than at TOA. The BB aerosol-induced atmospheric heating rate was up to 0.8–1.2 K/day in BB_param, which was larger than those in other experiments. Low cloud was enhanced while middle and high clouds were reduced by BB aerosols over northern MSEA. The BB aerosol-induced changes in cloud fractions in the BB_param experiment (up to 0.15 for low cloud and −0.05 for middle and high cloud) were approximately twice those in the other experiments. This study demonstrates the importance and necessity of properly representing the injection height of BB emissions in model estimation of radiative and climatic effects of BB aerosols. [Display omitted] • The direct radiative effects of four methods for BB injection height were explored. • Surface direct radiative effect of BB aerosols varied from −19 to −30 W m-2 among the methods. • BB aerosols induced the largest HR of 0.8–1.2 K/day at 3–5 km by the physically based method. • The BB aerosol-induced changes in cloud fraction with these methods varied by a factor of two. [ABSTRACT FROM AUTHOR]

Topic 3 of the Model Inter-Comparison Study for Asia (MICS-Asia) Phase III examines how online coupled air quality models perform in simulating wintertime haze events in the North China Plain region and evaluates the importance of aerosol radiative feedbacks. This paper discusses the estimates of aerosol radiative forcing, aerosol feedbacks, and possible causes for the differences among the participating models. Over the Beijing–Tianjin–Hebei (BTH) region, the ensemble mean of estimated aerosol direct radiative forcing (ADRF) at the top of atmosphere, inside the atmosphere, and at the surface are -1.1 , 7.7, and -8.8 W m -2 during January 2010, respectively. Subdivisions of direct and indirect aerosol radiative forcing confirm the dominant role of direct forcing. During severe haze days (17–19 January 2010), the averaged reduction in near-surface temperature for the BTH region can reach 0.3–1.6 ∘ C. The responses of wind speeds at 10 m (WS10) inferred from different models show consistent declines in eastern China. For the BTH region, aerosol–radiation feedback-induced daytime changes in PM 2.5 concentrations during severe haze days range from 6.0 to 12.9 µ g m -3 (<6 %). Sensitivity simulations indicate the important effect of aerosol mixing states on the estimates of ADRF and aerosol feedbacks. Besides, black carbon (BC) exhibits a large contribution to atmospheric heating and feedbacks although it accounts for a small share of mass concentration of PM 2.5. [ABSTRACT FROM AUTHOR]

By using WRF-Chem coupled with a heterogeneous reaction mechanism for sulfate formation, this study investigated the impact of meteorological condition and emission changes on chemical species, atmospheric oxidizing capacity (AOC), and secondary aerosol formation during the COVID-19 lockdown period from 23 January to April 8, 2020, focusing on a severe haze event on 7–14 February. The model with the new sulfate formation scheme reasonably reproduces the spatial-temporal distribution of meteorological variables and chemical species, and significantly improves predictions for both sulfate and SO 2 concentrations, as well as for PM 2.5 , ammonium, and nitrate to some extent. It is found that the adverse meteorological conditions were the main cause for the haze event formation, whereas emission reduction due to the lockdown somewhat decreased PM 2.5 concentration on average in the Beijing-Tianjin-Hebei (BTH) region. Compared with the same period in 2019, increased surface air temperature and relative humidity (RH) and decreased planetary boundary layer height (PBLH) facilitated accumulation of pollutants and formation of secondary aerosols during the haze episode in 2020, whereas the emission reduction due to the lockdown led to decreases in SO 2 , NO 2 , primary PM 2.5 (PPM 2.5), black carbon (BC), primary organic aerosols (POA), nitrate and ammonium concentrations, but increases in O 3 , sulfate and secondary organic aerosol (SOA) concentrations, due to the combined effect of changes in emissions and AOC. Gas and aqueous phase oxidation of SO 2 accounted for approximately 24% of sulfate formation, while the heterogeneous reaction of Mn-catalytic oxidation of SO 2 on aerosol surfaces dominated sulfate formation (76%) during the haze episode in the BTH region. Both adverse meteorological conditions and emission reductions increased heterogeneous sulfate formation rate mainly through altering aerosol surface area (ASA), pH, and Mn2+ concentration. Chemical species varied diversely during the three subperiods before (Period-1, 15–22 January) and during the lockdown (Period-2, 23 January to 5 March and Period-3, 6 March to 8 April) over the BTH. NO 2 concentration firstly decreased and then rebounded, whereas O 3 concentration increased gradually from the Period-1 to Period-3. All aerosols except SOA decreased throughout the lockdown period, whereas SOA peaked in the Period-2 due to its strong sensitivity to increasing AOC. Sulfate concentration decreased from the Period-1 to Period-2, mainly due to more adverse meteorological conditions in the Period-1, although sulfate increased slightly due to increasing AOC in the Period-2. The large difference in the direction and magnitude of species variations during the COVID-19 lockdown indicates the complex interplay among meteorology, emission, and chemistry. The model simulated mean differences in near surface species concentrations between the BASE and EMIS19 cases (BASE minus EMIS19) during the haze period of 7–14 February 2020, representing the impact of emission reduction due to the COVID-19 lockdown on the chemical species. The units for PM 2.5 and aerosol components are μg·m−3, and the units for SO 2 , NO 2 , and O 3 are ppb. [Display omitted] • Heterogeneous sulfate formation by Mn-catalytic reaction was coupled into WRF-Chem. • Haze event during the COVID lockdown was caused by adverse meteorological conditions. • Emission reduction led to a decrease in PM 2.5 in Beijing but increases in portions of the BTH. • Sulfate and SOA increased but nitrate decreased in the BTH in response to the lockdown. [ABSTRACT FROM AUTHOR]

A regional air quality model system (RAQMS), coupled with a biogenic emission model was applied to investigate the variations of summertime biogenic volatile organic compound (BVOC) emission and secondary organic aerosols (SOA) during 2001–2018 over China. During 2001–2018, evident land use changes occurred, especially in the Sichuan Basin, the Qinling Mountains, and the megacities over east China. Leaf aera index (LAI) increased significantly over the western parts of northeast China, the Qinling Mountains, the North China Plain (NCP), and most areas of south China. The domain-average LAI and BVOC emission increased by 0.2 m2 m−2 (19%) and 3.0 Tg (26%), respectively, over China during 2001–2018, mainly due to the increases in LAI and air temperature. It is found that near surface BSOA concentration increased apparently over China from 2001 to 2018, with the maximum increment exceeded 2 μg m−3 (75%) in the middle reaches of the Yangtze River. The domain-average surface BSOA concentration increased remarkably by 0.44 μg m−3 (41%) over China, resulting from the combined effect of LAI and anthropogenic emission increases, and meteorological change, in which the land use and LAI changes were the dominant driving factors, explaining over 50% of the BSOA increase, while the changes in meteorology and anthropogenic emission contributed almost equally to the remaining BSOA increase. The changes in near surface BSOA concentration (μg m−3) between summer 2001 and 2018 due to (a) land use and LAI changes; (b) meteorology change; (c) anthropogenic emission change; (d) all the above factor changes. [Display omitted] • Summer BVOC emissions and BSOA concentration over China during 2001–2018 are explored. • The domain-average LAI increased by 0.2 m2 m−2 (19%) over China from 2001 to 2018. • BVOC emissions in China increased by 3.0Tg (26%) due to increased LAI and air temperature. • BSOA concentration increased by 0.4 μg m−3 (41%) due to land use, meteorology, and anthropogenic emission variability. [ABSTRACT FROM AUTHOR]

A volatility basis set approach with chemical aging mechanism has been incorporated into a regional air quality model system (RAQMS) and used to investigate the distribution of organic aerosols (OA) over east China in April 2009, with focus on secondary organic aerosols (SOA) in fine particle and relative contributions from a series of anthropogenic and biogenic VOC precursors. The comparison between the VBS approach prediction and observation at four sites in east China demonstrates a significant improvement in SOA and OA concentrations compared with the traditional two-product model, which predicts very low SOA level. The average value of secondary organic carbon (SOC) for all sites predicted by the VBS approach with chemical aging is 2.8 μgC m −3 , quite close to the estimated value of 3.3 μgC m −3 . The SOC fraction of organic carbon (OC) also increases from just 5% predicted by the two-product model to 33% by the VBS approach with aging, close to the estimated fraction of 32%, suggesting a more realistic and precise representation of SOA formation by the VBS approach. The enhanced SOC prediction further improve OC prediction, reducing the normalized mean bias from −43% to −18%. The VBS approach with aging predicts SOA concentration in PM 2.5 of 5–10 μg m −3 over most parts of east China. The predicted ASOA concentrations vary from 5.0 to 7.5 μg m −3 in the Pearl River Delta, the Yangtze River Delta and the wide areas north of the Yangtze River. BSOA is predicted to be 1.0–2.5 μg m −3 across the regions from southeast China to the middle reaches of the Yangtze River and the Yellow River. Prediction with the VBS approach exhibits that ASOA becomes dominant component of SOA, which is more realistic as compared to the BSOA dominance by the two-product model. The domain-average surface POA and SOA concentrations predicted by the VBS approach with aging over east China are 4.86 μg m −3 and 4.45 μg m −3 , with the SOA fraction of total OA and the ASOA fraction of SOA being 48% and 85%, respectively. This indicates the comparable contributions to OA from SOA and POA, and the predominant contribution of ASOA to SOA over east China in springtime. The mean SOA concentrations over east China produced from aromatics, alkanes, alkenes, isoprene, monoterpene and sesquiterpene are predicted to be 2.44, 0.57, 0.8, 0.17, 0.42 and 0.06 μg m −3 , respectively, which contribute 55%, 13%, 18%, 4%, 9% and 1% of the total SOA. Aromatics are the dominant contributors to SOA formation. [ABSTRACT FROM AUTHOR]

Various precursor emissions and chemical mechanisms for secondary organic aerosol (SOA) formation were incorporated into a regional air quality model system (RAQMS) and applied to investigate the distribution, composition, and source contribution of SOA over east China in summer 2018. Model comparison against a variety of observations at a national scale demonstrated that the model was able to reasonably reproduce meteorological variables, O 3 and PM 2.5 concentrations, and the model simulated SOA concentration generally agreed with observations, with the overall NMB of 7.0% and R of 0.4 in 10 cities over east China. The simulated period-mean SOA concentrations of 4–15 μg m−3 were mainly distributed over the North China Plain (NCP), the middle and lower reaches of the Yangtze River and Chongqing district. SOA dominated organic aerosol (OA) over China in summertime (90%). The percentage contributions to SOA from ASOA (SOA produced from anthropogenic volatile organic compounds (AVOC)), BSOA (SOA produced from biogenic volatile organic compounds (BVOC)), DSOA (SOA produced from aqueous uptake of glyoxal and methylglyoxal) and S/I-SOA (SOA produced from semi-volatile and intermediate volatile organic compounds) were estimated to be 48.3%, 28.6%, 14.3%, and 8.8% respectively, over east China in summertime. In terms of domain and period average, ASOA contributed most to SOA (59%) in north China, while BSOA contributed most to SOA (37.3%) in northeast China. The percentage contribution of DSOA to SOA reached 21.5% in southwest China. S/I-SOA accounted for approximately 10% of SOA in most areas of east China. This study reveals that while AVOC dominates SOA formation on average over east China, the SOA source contributions differ considerably in different regions of China. BVOC makes the same contribution to SOA formation as AVOC in northeast China and southwest China, where forest coverage and BVOC emission are higher and anthropogenic emissions are relatively low, highlighting the significant role of BVOC in summer SOA formation in China. The model simulated average (a) surface SOA concentration (unit: μg m−3) and percentage contributions (%) of individual precursors and chemical pathways to surface SOA concentration (b) over east China (average of the 4 sub-regions), and (c-f) over the four sub-regions of China in summer 2018. (Note ARO, PAR, OLE denote aromatics, alkanes, alkenes; ISOP, TERP, SESQ denote isoprene, monoterpenes, and sesquiterpenes, respectively.). [Display omitted] • The model with multiple chemical pathways reproduces SOA reasonably well. • Source contributions to summer SOA over China are explored and quantified. • AVOC, BVOC, S/IVOC and dicarbonyls contribute 48%, 29%, 9%,14% of SOA mass. • BVOC and AVOC contribute equally to SOA formation in northeast and southwest China. [ABSTRACT FROM AUTHOR]

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

A regional air quality model system (RAQMS) was developed by incorporating an aqueous reaction mechanism for secondary organic aerosol (SOA) formation and primary semi-volatile (SVOC) and intermediate volatile organic compounds (IVOC) precursors to investigate various chemical pathways for SOA formation in the Beijing-Tianjin-Hebei (BTH) region in wintertime. Model comparison against observations demonstrates that the model is able to well reproduce meteorological variables and major aerosol chemical components, and the model improves SOA simulation significantly by including primary S/IVOCs (SVOC + IVOC) and aqueous reactions into the model. SVOC and IVOC emissions were relatively higher over the regions from southern Hebei province to Beijing and Tianjin, with the emission rates up to 0.15 mg m−2 hr−1 and 0.3 mg m−2 hr−1, respectively. The glyoxal (GLY) and methylglyoxal (MGLY) emissions were similar in distribution to those of S/IVOC emissions, with the maximum of 0.08 mg m −2 hr−1. The simulated SOA concentrations exhibited a southwest-northeast belt extending from southern Hebei to Beijing, with the maximum of 35 μg m−3 in southern Hebei province. The average contributions from various precursors or chemical pathways to SOA formation during the study period were estimated, in which AVOCs (anthropogenic VOCs), SVOCs, IVOCs, BVOCs (biogenic VOCs), GLY and MGLY contributed 38.4%, 24.9%, 28.4%, 0.2% and 8.1% of SOA mass concentration, respectively, in the BTH region. The maximum average contribution of GLY and MGLY to SOA reached 16% in southern Hebei province during a severe haze episode. From the clean to haze periods, concentrations of all SOA components apparently increased along with increasing atmospheric stability and weakening dispersion, but the increasing rates of SOA concentration produced by AVOCs and aqueous reactions were larger than those by primary S/IVOCs due to different chemical processes, and the AVOC-produced SOA dominated over the other SOA components during the haze periods. Figure Contributions (%) of various chemical pathways to surface SOA concentration in PM 2.5 during the entire study period (a, e), haze episode 1 (b, f), haze episode 2 (c, g) and haze episode 3 (d, h) in Beijing (a, b, c. d) and in the BTH region (e, f, g, h). Image 1 • Various chemical formation pathways for SOA are explored and quantified. • SOA simulation is remarkedly improved by inclusion of new pathways. • Primary S/IVOC precursors play an important role in SOA formation. • Aqueous uptake of dicarbonyls contributes up to 16% of SOA in haze days. [ABSTRACT FROM AUTHOR]

Abstract: The air quality modeling system RAMS-CMAQ is developed to assess aerosol direct radiative forcing by linking simulated meteorological parameters and aerosol mass concentration with the aerosol optical properties/radiative transfer module in this study. The module is capable of accounting for important factors that affect aerosol optical properties and radiative effect, such as incident wave length, aerosol size distribution, water uptake, and internal mixture. Subsequently, the modeling system is applied to simulate the temporal and spatial variations in mass burden, optical properties, and direct radiative forcing of diverse aerosols, including sulfate, nitrate, ammonium, black carbon, organic carbon, dust, and sea salt over East Asia throughout 2005. Model performance is fully evaluated using various observational data, including satellite monitoring of MODIS and surface measurements of EANET (Acid Deposition Monitoring Network), AERONET (Aerosol Robotic Network), and CSHNET (Chinese Sun Hazemeter Network). The correlation coefficients of the comparisons of daily average mass concentrations of sulfate, PM2.5, and PM10 between simulations and EANET measurements are 0.70, 0.61, and 0.64, respectively. It is also determined that the modeled aerosol optical depth (AOD) is in congruence with the observed results from the AERONET, the CSHNET, and the MODIS. The model results suggest that the high AOD values ranging from 0.8 to 1.2 are mainly distributed over the Sichuan Basin as well as over central and southeastern China, in East Asia. The aerosol direct radiative forcing patterns generally followed the AOD patterns. The strongest forcing effect ranging from −12 to −8 W m−2 was mainly distributed over the Sichuan Basin and the eastern China’s coastal regions in the all-sky case at TOA, and the forcing effect ranging from −8 to −4 W m−2 could be found over entire eastern China, Korea, Japan, East China Sea, and the sea areas of Japan [Copyright &y& Elsevier]

Carbonaceous aerosol, mainly comprising elemental carbon (EC) and organic carbon (OC), plays an important role in aerosol–climate interaction owing to its light-absorbing feature. The radiative forcing of carbonaceous aerosol is largely determined by its mass absorption efficiency (MAE). To depict the MAE of carbonaceous aerosol and its variations with aerosol size and chemical composition, light absorption coefficients and the main chemical composition of PM 1 and PM 2.5 were comparably measured in a winter field campaign in urban Beijing. On average, aerosol absorption by PM 1 at 880 nm wavelength contributes to approximately half of aerosol absorption by PM 2.5 , mainly because aerosol absorption at this wavelength was dominated by EC and nearly half of the total EC mass in PM 2.5 existed in PM 1. The average MAE of EC at 880 nm (MAE EC,880nm) was 3.9 ± 0.7 m2 g−1 for PM 2.5 , lower than that for PM 1 (4.4 ± 0.8 m2 g−1) likely because of the larger EC cores and lower coating degrees of EC particles in PM 1–2.5. Variation in MAE EC,880nm was related to the bulk mass fractions of nitrate in PM 1 and PM 2.5 , implying the important impact of secondary nitrate formation on the modification of EC mixing states and enhancing EC absorption efficiency in Beijing. Absorption by OC took up about 40% of the absorption coefficients for PM 1 and PM 2.5 at 370 nm. The mean MAE of OC at 370 nm (MAE OC,370nm) was 2.4 ± 0.9 m2 g−1 for PM 1 , higher than that of for PM 2.5 (1.9 ± 0.6 m2 g−1). The high value of MAE OC,370nm might be associated with regionally transported aerosols during clean and polluted periods. Enlarged particle sizes might have considerably weakened MAE OC,370nm for PM 2.5 while exerting negligible impact on MAE OC,370nm for PM 1. • Light absorption capacity of elemental carbon and organic carbon aerosols was compared between PM 1 and PM 2.5. • Nitrate was found to be the main aerosol chemical composition affecting the mass absorption efficiency (MAE) of EC. • MAE of EC in PM 2.5 was lower than that in PM 1 owing to large core sizes and low coating degrees of EC particles in PM 1–2.5. • Enlarged particle sizes in polluted periods might have weakened MAE of OC for PM 2.5. [ABSTRACT FROM AUTHOR]

Biomass burning emissions (agriculture and forest) are one of the major contributors to air pollution over Thailand during the hot-dry season (March–April) and aerosols from biomass burning can adversely affect the weather and produce health effects (respiratory disease, heart disease etc.). The present study investigated the sensitivity of aerosol chemistry schemes (Goddard Chemistry Aerosol Radiation and Transport, GOCART; Model for Simulating Aerosol Interactions and Chemistry, MOSAIC) on spatio-temporal distributions of simulated PM 2.5 (particle sizes <2.5 μm) mass concentrations. Also, the study looked into the impact of PM 2.5 on meteorology during an intense biomass burning period (15 March – 15 April 2019) using an online regional chemical transport model, Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). PM 2.5 mass concentrations were observed over the northern regions of Thailand varying from 40 to 240 μg m−3. The simulations using GOCART and MOSAIC aerosol scheme were able to capture the spatio-temporal variations of PM 2.5 mass concentrations in general. However, it underestimated the observation magnitudes by about 24% and 27%, respectively. In addition, the sensitivy of EDGAR-HTAP (Emission Database for Global Atmospheric Research collaboratively with the task force for Hemispheric Transport of Air Pollution) and CAMS-GLOB-ANT (Copernicus Atmosphere Monitoring Service Global) anthropogenic emission inventories on PM 2.5 mass were investigated using the model. The simulated aerosol mass concentrations from EDGAR-HTAP found more realistic emissions when compared to CAMS-GLOB-ANT in most of the regions. The discrepancy in the simulation of aerosol mass concentrations could be attributed to uncertainties in the emission inventories, weak representation of secondary aerosol compositions, as well as the overestimation of wind speed and wet scavenging in the model. The study also investigated the influence of aerosols on meteorology by comparing a simulation with aerosol-radiation-interaction to a simulation without aerosol-radiation-interaction in the atmosphere during the time period. Significant changes in meteorological parameters were observed over regions having higher aerosol mass concentrations with a reduction of about 26% in solar insolation, 3.9% in near surface temperature, 21% in planetary boundary layer height and an increase of 13% in relative humidity. • Observed PM 2.5 ranges 40–240 μg m−3 over northern Thailand during biomass burning. • WRF-Chem is able to capture the spatio-temporal variabilties of PM 2.5 over Thailand. • Model using the GOCART aerosol scheme performed better than the MOSAIC scheme. • Aerosols reduced surface temperature by 3.6% and PBLH by 21%. [ABSTRACT FROM AUTHOR]

Heavy aerosol loading over the Bohai Bay, the innermost gulf of the Yellow Sea, was often recorded by the satellite observations. In order to understand aerosol optical properties and potential causes for the high aerosol loading there, a Cimel sunphotometer station (BH) was established on an offshore platform over the Bay for the first time in June 2012. The aerosol optical properties between July 2012 and July 2013 were employed to validate the satellite retrievals and to characterize temporal variability of aerosol optical properties. In particular, aerosol optical properties at BH were compared with those at Beijing (BJ), an urban station of the North China Plain (NCP), to discuss their potential difference during the same months of the same years. Mean aerosol optical depth at 550 nm (AOD) retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) measurements over the Bohai Bay was 0.79 ± 0.68 during 2004–2013, that even exceeded value over the NCP (0.50 ± 0.57). This fact was supported by the comparison of ground-based remote sensing AODs at BH and BJ. The annual mean Cimel AOD at BH was 0.76 ± 0.62, which was larger than that at BJ (0.64 ± 0.52). The MODIS AOD difference between the Bohai Bay and the NCP was 0.29, being more than two times larger than the Cimel AOD difference between BH and BJ (0.12). This strongly implied that the MODIS retrievals had significant biases over the Bohai Bay that was likely due to sediment in the water and also sea ice in winter. A distinct seasonal variation of AOD was revealed over ocean. The maxima Cimel AOD was observed in summer (1.02 ± 0.75), which was followed by spring (0.86 ± 0.61), autumn (0.54 ± 0.41), and winter (0.39 ± 0.24); this was in good agreement with that over the NCP. High AOD over the Bohai Bay was associated with the heavy exhaust emissions from the ships across the Bay and transport of aerosols from the NCP. Furthermore, a much strong hygroscopic growth of fine mode aerosols over the Sea as a result of humid environment also should contributed to high AOD. This was supported by the observation that the effective radius and fraction of fine mode increased with AOD at the Bay, more importantly, the increasing rate was always larger than that at the NCP. The knowledge of the detailed variations of aerosol optical properties over the polluted ocean region would help to improve satellite aerosol retrieval and to promote our understanding on regional climate change research. [ABSTRACT FROM AUTHOR]

Abstract: A continuous observation of organic carbon (OC) and elemental carbon (EC), and PM10 was conducted at an urban site of Beijing to investigate the characterization of carbonaceous aerosols during spring time. The mean value and standard deviations of OC, EC, PM10 concentration, and OC/EC ratio were 13.5±7.0μgm−3, 7.1±4.1μgm−3, 187.8±136.9μgm−3, and 2.0±0.4, respectively. OC, EC, and total carbonaceous aerosols (TCA) in PM10 account for 9.3±5.7%, 4.7±2.7%, and 19.6±11.6%, respectively. Good correlations (R 2 =0.7) between OC and EC were observed in spring season. Average OC concentrations are 13.5μgm−3 in both daytime and nighttime. Average EC concentrations in daytime (7.4μgm−3) are slightly higher than those in nighttime (6.8μgm−3). Both OC and EC concentrations reach maximum value in morning time (07:30–10:30) due to motor vehicles during the traffic rush hour. PM10, OC, and EC concentration increase while PM2.5 concentration, OC/EC ratio, PM2.5/PM10, and TCA/PM10 ratio decrease in dust period in Beijing. During the observation period, the carbonaceous aerosols from motor vehicle and coal combustion accounted for 76% and 24%, respectively. It shows that the motor vehicle represents the dominant emitter of carbonaceous aerosols associated with PM10 in Beijing during spring time. [Copyright &y& Elsevier]

Abstract: The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is applied to East Asia to analyze the production and transport processes of sulfur compounds in the springtime of 2001, when two large field campaigns TRACE-P (TRAnsport and Chemical Evolution over the Pacific) and ACE-Asia (Aerosol Characterization Experiment – Asia) were being conducted over a broad area covering northeastern Asia and the western pacific. Simulated concentrations of sulfur dioxide (SO2) and sulfate aerosol (SO4 2−) were compared with observed data obtained on the ground level at three remote sites in South Korea and China and onboard aircraft C130, and it was found that the modeling system reproduced many of the important features in the observations, including horizontal and vertical gradients, of the Asian pollution outflow over the western Pacific. Analysis of model results shows that the SO2 and SO4 2− concentrations exhibited pronounced variations in time and space, with SO2 and SO4 2− behaving differently due to the interplay of chemical conversion, removal and transport processes. [Copyright &y& Elsevier]