Aerosol Species Research Articles

Modeling the Influence of Ions on the Dynamics of Formation of Atmospheric Aerosol

This paper describes a new numerical model of transport and transformation of gaseous and aerosol species in the atmosphere incorporating photochemistry, nucleation with neutral molecules and ions, condensation/evaporation, and coagulation. The results of calculations of the temporal variability of the calculated concentrations, the spectrum of aerosol particles in the atmosphere, and the rates of nucleation processes are presented. The results for the Northern Hemisphere in winter conditions indicate the significant role of the process of ion nucleation in the formation of aerosol. In addition to air ionization, temperature and relative humidity are among the key factors determining the dynamics of ion nucleation.

Aerosol and Gas Phase Concentrations from an Adapted Annular Denuder System in a Broiler Housing Facility

HighlightsAn adapted annular denuder system (ADS) was implemented in a broiler facility to measure secondary aerosols.Results show that secondary aerosols were not always associated with ammonium or ammonia.Chloride aerosols were significant in comparison to other species and were present at consistent concentrations.This study concludes that the chloride source was the feed in the feeding pans.Abstract. Fine particulate matter (PM2.5) is present in animal housing facilities from both primary and secondary sources. Measuring secondary aerosols in harsh environments with high gas and particulate concentrations, such as poultry housing facilities, is an ongoing challenge. This study presents the results from the implementation of an adapted annular denuder system (ADS) used to measure secondary PM2.5 from inside a broiler facility in Ontario, Canada. Results from this work show that secondary aerosols formed the majority of total PM2.5 during the early portion of the growth cycle. It was further determined that the ion balance between ammonium and anions was not consistent, leading to the conclusion that a significant portion of the aerosol species are associated with a previously unidentified source that is not necessarily due to secondary reactions. Keywords: Ammonia, Annular denuder system, Particulate matter, Poultry, Secondary aerosols.

Analysis of aerosol distribution variations over China for the period 2045–2050 under different Representative Concentration Pathway scenarios: 不同代表性浓度路径情景下 2045-2050 年中国气溶胶分布变化的分析

The regional air quality modeling system RAMS-CMAQ was applied to simulate the aerosol concentration for the period 2045–2050 over China based on the downscaled meteorological field of three RCP scenarios from CESM (NCAR's Community Earth System Model) in CMIP5. The downscaling simulation of the meteorological field of the three RCP scenarios showed that, compared with that under RCP2.6, the difference in near-surface temperature between North and South China is weakened and the wind speed increases over North and South China and decreases over central China under RCP4.5 and RCP8.5. Under RCP2.6, from 2045 to 2050, the modeled average PM2.5 concentration is highest, with a value of 40–50 µg m−3, over the North China Plain, part of the Yangtze River Delta, and the Sichuan Basin. Meanwhile, it is 30–40 µg m−3 over central China and part of the Pearl River Delta. Compared with RCP2.6, PM2.5 increases by 4–12 µg m−3 under both RCP4.5 and RCP8.5, of which the SO42− and NH4+ concentration increases under both RCP4.5 and RCP8.5; the NO3− concentration decreases under RCP4.5 and increases under RCP8.5; and the black carbon concentration changes very slightly, and organic carbon concentration decreases, under RCP4.5 and RCP8.5, with some increase over part of Southwest and Southeast China under RCP8.5. The difference between RCP4.5 and RCP2.6 and the difference between RCP8.5 and RCP2.6 have similar annual variation for different aerosol species, indicating that the impact of climate change on different species tends to be consistent.摘要基于来自于 CMIP5 中 CESM 模式的三种 RCP 情景下的气象场的降尺度模拟, 应用区域空气质量模式系统 RAMS-CMAQ 模拟 2045-2050 年中国地区气溶胶浓度.三种 RCP 情景下气象场的降尺度模拟表明, 与 RCP2.6 相比, 在 RCP4.5 和 RCP8.5 下, 华北和华南的近地表温度差减小, 风速在华北和华南地区增加, 在中部地区下降. RCP2.6 情景下, 模拟的 2045 年到 2050 年平均的 PM 2.5浓度在华北平原, 长三角的部分地区和四川盆地最高, 约为 40-50 µg m–3, 在中国中部和珠三角的部分地区约为 30-40 µg m–3. 与 RCP2.6 相比, 在 RCP4.5 和 RCP8.5 下, PM2.5增加了 4-12 µg m–3, 其中在 RCP4.5 和 RCP8.5 下, SO42–和 NH4+的浓度增加, 在 RCP4.5 下, NO3–浓度降低, 在 RCP8.5 下, NO3–浓度升高, 在 RCP4.5 和 RCP8.5 下, BC 浓度变化很小, 而 OC 浓度下降, 其中在 RCP8.5 下, 西南和东南部分地区的 OC 有所增加.不同的气溶胶物种浓度在 RCP4.5 和 RCP2.6 之间的差异以及 RCP8.5 和 RCP2.6 之间的差异具有相似的年度变化, 这表明气候变化对不同物种的影响趋于一致.

Description and evaluation of aerosol in UKESM1 and HadGEM3-GC3.1 CMIP6 historical simulations

Abstract. We document and evaluate the aerosol schemes as implemented in the physical and Earth system models, the Global Coupled 3.1 configuration of the Hadley Centre Global Environment Model version 3 (HadGEM3-GC3.1) and the United Kingdom Earth System Model (UKESM1), which are contributing to the sixth Coupled Model Intercomparison Project (CMIP6). The simulation of aerosols in the present-day period of the historical ensemble of these models is evaluated against a range of observations. Updates to the aerosol microphysics scheme are documented as well as differences in the aerosol representation between the physical and Earth system configurations. The additional Earth system interactions included in UKESM1 lead to differences in the emissions of natural aerosol sources such as dimethyl sulfide, mineral dust and organic aerosol and subsequent evolution of these species in the model. UKESM1 also includes a stratospheric–tropospheric chemistry scheme which is fully coupled to the aerosol scheme, while GC3.1 employs a simplified aerosol chemistry mechanism driven by prescribed monthly climatologies of the relevant oxidants. Overall, the simulated speciated aerosol mass concentrations compare reasonably well with observations. Both models capture the negative trend in sulfate aerosol concentrations over Europe and the eastern United States of America (US) although the models tend to underestimate sulfate concentrations in both regions. Interactive emissions of biogenic volatile organic compounds in UKESM1 lead to an improved agreement of organic aerosol over the US. Simulated dust burdens are similar in both models despite a 2-fold difference in dust emissions. Aerosol optical depth is biased low in dust source and outflow regions but performs well in other regions compared to a number of satellite and ground-based retrievals of aerosol optical depth. Simulated aerosol number concentrations are generally within a factor of 2 of the observations, with both models tending to overestimate number concentrations over remote ocean regions, apart from at high latitudes, and underestimate over Northern Hemisphere continents. Finally, a new primary marine organic aerosol source is implemented in UKESM1 for the first time. The impact of this new aerosol source is evaluated. Over the pristine Southern Ocean, it is found to improve the seasonal cycle of organic aerosol mass and cloud droplet number concentrations relative to GC3.1 although underestimations in cloud droplet number concentrations remain. This paper provides a useful characterisation of the aerosol climatology in both models and will facilitate understanding in the numerous aerosol–climate interaction studies that will be conducted as part of CMIP6 and beyond.

Simulating and Evaluating Global Aerosol Distributions With the Online Aerosol‐Coupled CAS‐FGOALS Model

AbstractWe implement an existing aerosol module named Spectral Radiation Transport Model for Aerosol Species (SPRINTARS) in the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System (CAS‐FGOALS) model and simulate the global aerosol properties over 2002–2014. The simulated surface mass concentrations of individual aerosols generally reproduce the observed ones. The simulated spatial‐temporal distributions of the aerosol optical depths (AODs) are evaluated with multisource satellite retrievals, and the simulated AOD, Ångström Exponent (AE), and single scattering albedo (SSA) are further evaluated with the ground‐based Aerosol Robotic Network (AERONET) measurements. The spatial distribution of the modeled AOD is found to be generally comparable to the satellite retrievals. The interannual and seasonal variations of the modeled AOD over various aerosol regimes are also overall consistent with the AERONET observations. With respect to the AE, our model can reproduce the interannual variations fairly well over the dust dominant regions, and generally capture the seasonal variations over the industrial domain regions. Over the industrial domain regions, however, the systematic underestimation of the simulated AE is found, which is in part due to the biases of wind fields and overestimation of the relative humidity (RH) by the host model. With respect to the SSA, our model can also generally reproduce the observed seasonal variations, while the modeled values are typically lower than the observations, especially over North Africa.

Impacts of the meteorological condition versus emissions reduction on the PM2.5 concentration over Beijing–Tianjin–Hebei during the COVID-19 lockdown

The impacts of the meteorological condition and emissions reduction on the aerosol concentration over the Beijing–Tianjin–Hebei (BTH) region during the COVID-19 lockdown were analyzed by conducting three numerical experiments, including one with the meteorological field in 2019 and MEIC-2019 (2019 monthly Multi-resolution Emissions Inventory for China), one with the meteorological field in 2020 and MEIC-2019, and one with the meteorological field in 2020 and MEIC-2020, via a WRF-Chem model. The numerical experiments were performed from 3 to 16 February in 2019 and in 2020, during which a severe fog–haze event (3–16 February 2020) occurred in the BTH region, with a simulated maximum daily PM2.5 of 245 μg m−3 in Tangshan and 175 μg m−3 in Beijing. The results indicate that the daily PM2.5 decreased by 5–150 μg m−3 due to the emissions reduction and increased by 10–175 μg m−3 due to the meteorological condition in Beijing, Shijiazhuang, Cangzhou, Handan, Hengshui, Chengde, Zhangjiakou, and Tangshan from 7 to 14 February. For the horizontal distribution, PM2.5 and different aerosol species concentrations from 7 to 14 February 2020 increased compared with those during the same period in 2019, indicating that the accumulation of pollutants caused by the unfavorable meteorological condition offset the decreases caused by the emissions reduction, leading to the high aerosol concentration during the COVID-19 lockdown.摘要本研究从气象条件和减排两方面探讨了COVID-19封锁期间严重雾霾发生的原因[研究目的], 并定量的分析了气象条件和减排对PM2.5浓度的相对影响[创新点].使用WRF-Chem在2019年2月3日–16日和2020年2月3日–16日进行了三个数值模拟试验, 分别为2019年气象场与MEIC-2019 (2019年中国多分辨率月度排放清单) ,2020年气象场与MEIC-2019,2020年气象场与MEIC-2020[研究方法].结果表明COVID-19封锁期间严重雾霾的原因是不利气象条件增加的PM2.5浓度大于减排减少的PM2.5浓度[重要结论].

Characteristics, evolution, and potential source regions of submicron aerosol in Beijing, China

Atmospheric fine particulate pollution has been a dramatically environmental concern in all seasons in the megacity Beijing in recent years. A long-term real-time monitoring campaign of non-refractory submicron aerosol (NR-PM1) at a southeastern urban site in Beijing from July 13, 2017 to May 26, 2018 using an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was carried out to investigate the characteristics and evolution processes of NR-PM1 and its potential source effects. The annual average concentration of NR-PM1 during the entire study period was 40.8 μg/m3, lower than that of NR-PM1 from July 2011 to June 2012, and its seasonal variation presented the order of autumn and spring > winter > summer. The average concentration of organic species Org in the entire study was 15.1 μg/m3 and accounted for 37% of NR-PM1, being consistently a significant component of NR-PM1 in the four seasons. The average concentrations of SO42− and NO3− were 8.6 and 11.1 μg/m3, respectively, accounting for 21% and 27% of NR-PM1, and NO3− and its contribution to NR-PM1 exceeded those of SO42−, suggesting that secondary nitrate became a more dramatic pollutant. Note that SO42− in summer accounted for 27% of NR-PM1, higher than those in the other seasons, indicating that secondary sulfate formation was greatly important in summer, however, NO3− in summer accounted for 22% of NR-PM1, lower than those in the other seasons, more likely due to relatively high temperature in summer being favorable for dissociation of nitrate. NH4+ and Cl− species presented lower mass concentrations and mass fractions, and the seasonal variation of NH4+ was similar to NO3−, yet Cl− presented a typical seasonal change related to intense fossil fuel combustion during the heating period in winter and biomass burning in autumn with an order of winter > autumn > spring > summer. All aerosol species exhibited different diurnal cycles, of which Org presented a bimodal mode, SO42− and Cl− showed a flatter diurnal pattern, however, NO3− and NH4+ displayed more similar single-peak patterns. The conversion of SO2 to SO42− presented an obvious seasonal variation with summer > autumn > spring > winter driven by different factors. The conversion of NO2 to NO3− also showed a significant seasonal change characterized by autumn > summer and spring > winter controlled by different factors. Relative humidity, temperature and wind speed during the study period were significant meteorological elements influencing NR-PM1 and its species, and heavy haze pollution episodes largely occurred under high relative humidity and low wind speed. High potential source regions influencing NR-PM1 pollution in Beijing in all seasons presented dramatically distributions related to wind directions.

In-cloud scavenging scheme for sectional aerosol modules – implementation in the framework of the Sectional Aerosol module for Large Scale Applications version 2.0 (SALSA2.0) global aerosol module

Abstract. In this study we introduce an in-cloud wet deposition scheme for liquid and ice phase clouds for global aerosol–climate models which use a size-segregated aerosol description. For in-cloud nucleation scavenging, the scheme uses cloud droplet activation and ice nucleation rates obtained from the host model. For in-cloud impaction scavenging, we used a method where the removal rate depends on the wet aerosol size and cloud droplet radii. We used the latest release version of ECHAM-HAMMOZ (ECHAM6.3-HAM2.3-MOZ1.0) with the Sectional Aerosol module for Large Scale Applications version 2.0 (SALSA) microphysics package to test and compare our scheme. The scheme was compared to a scheme that uses fixed scavenging coefficients. The comparison included vertical profiles and mass and number distributions of wet deposition fluxes of different aerosol compounds and for different latitude bands. Using the scheme presented here, mass concentrations for black carbon, organic carbon, sulfate, and the number concentration of particles with diameters larger than 100 nm are higher than using fixed scavenging coefficients, with the largest differences in the vertical profiles in the Arctic. On the other hand, the number concentrations of particles smaller than 100 nm in diameter show a decrease, especially in the Arctic region. These results could indicate that, compared to fixed scavenging coefficients, nucleation scavenging is less efficient, resulting in an increase in the number concentration of particles larger than 100 nm. In addition, changes in rates of impaction scavenging and new particle formation (NPF) can be the main cause of reduction in the number concentrations of particles smaller than 100 nm. Without further adjustments in the host model, our wet deposition scheme produced unrealistically high aerosol concentrations, especially at high altitudes. This also leads to a spuriously long lifetime of black carbon aerosol. To find a better setup for simulating aerosol vertical profiles and transport, sensitivity simulations were conducted where aerosol emission distribution and hygroscopicity were altered. Vertical profiles of aerosol species simulated with the scheme which uses fixed scavenging rates and the abovementioned sensitivity simulations were evaluated against vertical profiles from aircraft observations. The lifetimes of different aerosol compounds were also evaluated against the ensemble mean of models involved in the Aerosol Comparisons between Observations and Models (AEROCOM) project. The best comparison between the observations and the model was achieved with our wet deposition scheme when black carbon was emitted internally mixed with soluble compounds instead of keeping it externally mixed. This also produced atmospheric lifetimes for the other species which were comparable to the AEROCOM model means.

Impact of Meteorological Changes on Particulate Matter and Aerosol Optical Depth in Seoul during the Months of June over Recent Decades

The effects of meteorological changes on particulate matter with a diameter of 10 microns or less (PM10, referred to as PM in this study) and aerosol optical depth (AOD) in Seoul were investigated using observational and modeling analysis. AOD satellite data were used, obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS), and PM concentration data were used from in-situ observations. The Modern-Era Retrospective Analysis for Research and Applications (MERRA) and MERRA Version 2 (MERRA-2) were used for meteorological field analysis in modeling and observation data. The results from this investigation show that meteorological effects on PM and AOD were strong in the month of June, revealing a clear decreasing trend in recent decades. The investigation focused on the underlying mechanisms influencing the reduction in PM resulting from meteorological changes during the months of June. The results of this study reveal that decreases in atmospheric stability and humidity induced the aerosol change observed in recent decades. The changes in atmospheric stability and humidity are highly correlated with changes in the intensity of the East Asian summer monsoon (EASM). This suggests that the unstable and drying atmosphere by weakening of the EASM in recent decades has improved PM air quality in Seoul during the summer. The effects of atmospheric stability and humidity were also observed to vary depending on the aerosol species. Humidity only affects hydrophilic aerosols such as sulfate, nitrate, and ammonium, whereas atmospheric stability affects all species of aerosols, including carbonaceous aerosols.

Interferences with aerosol acidity quantification due to gas-phase ammonia uptake onto acidic sulfate filter samples

Abstract. Measurements of the mass concentration and chemical speciation of aerosols are important to investigate their chemical and physical processing from near emission sources to the most remote regions of the atmosphere. A common method to analyze aerosols is to collect them onto filters and analyze the filters offline; however, biases in some chemical components are possible due to changes in the accumulated particles during the handling of the samples. Any biases would impact the measured chemical composition, which in turn affects our understanding of numerous physicochemical processes and aerosol radiative properties. We show, using filters collected onboard the NASA DC-8 and NSF C-130 during six different aircraft campaigns, a consistent, substantial difference in ammonium mass concentration and ammonium-to-anion ratios when comparing the aerosols collected on filters versus an Aerodyne aerosol mass spectrometer (AMS). Another online measurement is consistent with the AMS in showing that the aerosol has lower ammonium-to-anion ratios than obtained by the filters. Using a gas uptake model with literature values for accommodation coefficients, we show that for ambient ammonia mixing ratios greater than 10 ppbv, the timescale for ammonia reacting with acidic aerosol on filter substrates is less than 30 s (typical filter handling time in the aircraft) for typical aerosol volume distributions. Measurements of gas-phase ammonia inside the cabin of the DC-8 show ammonia mixing ratios of 45±20 ppbv, consistent with mixing ratios observed in other indoor environments. This analysis enables guidelines for filter handling to reduce ammonia uptake. Finally, a more meaningful limit of detection for University of New Hampshire Soluble Acidic Gases and Aerosol (SAGA) filters collected during airborne campaigns is ∼0.2 µg sm−3 of ammonium, which is substantially higher than the limit of detection of ion chromatography. A similar analysis should be conducted for filters that collect inorganic aerosol and do not have ammonia scrubbers and/or are handled in the presence of human ammonia emissions.

Assessment of the vertical distribution of speciated aerosol absorption over South Asia using spaceborne LIDAR and ground-based observations

Present study estimates the shortwave radiative effects of absorbing aerosols (dust and carbonaceous aerosols) over the Indian landmass using a synergy of spaceborne and ground-based observations. Vertical profiles of dust and total aerosols are estimated using the multi-year (2006–2017) observations from CALIOP (Cloud Aerosol Lidar with Orthogonal Polarization) over the Indian region. Pre-monsoon enhancement (March ‐ –May) in aerosol loading over the Indian region is significantly contributed (~56%) by the transported mineral dust at free tropospheric altitudes. Though, shortwave radiative effect due to dust in the atmosphere increases about three times from winter to pre-monsoon, at the top of the atmosphere (TOA) it causes cooling. Dust induced cooling reverses the positive radiative effect induced by non-dust aerosols at TOA over Indo-Gangetic Plains. Though the natural dust dominates the aerosol loading during pre-monsoon, anthropogenic dust contributes significantly (~65%) to the total dust loading during winter. Over Indo-Gangetic Plains, high aerosol warming (up to ~2 Kday−1) observed within the planetary boundary layer (PBL) is mainly caused by carbonaceous aerosols (85%). The observed heating rates over the Indian region can have significant implications over regional climate, air quality, and changing precipitation patterns.

JWST Transit Spectra. II. Constraining Aerosol Species, Particle-size Distributions, Temperature, and Metallicity for Cloudy Exoplanets

Abstract The James Webb Space Telescope (JWST) will provide moderate-resolution transit spectra with continuous wavelength coverage from the optical to the mid-infrared for the first time. In this paper, we illustrate how different aerosol species, size distributions, and spatial distributions encode information in the JWST transit spectra of warm exoplanets. We use the transit spectral modeling code METIS, along with Mie theory and several flexible treatments of aerosol size and spatial distributions to perform parameter sensitivity studies, calculate transit contribution functions, compute Jacobians, and retrieve parameters from simulated data. The broader wavelength coverage of the JWST can encompass enough non-gray aerosol behavior to recover information about the species and size distribution of particles under many feasible aerosol scenarios. Within the JWST wavelength range, the optical and mid-infrared typically provide information about 0.1–1 μm sized aerosols, while the near-infrared to mid-infrared wavelengths usually provide information about gaseous absorption. Strong gaseous absorption features in the infrared can remain visible, even when clouds and hazes are flattening the optical and near-infrared portion of the spectrum that is currently observable. For some combinations of aerosol properties, temperature, and surface gravity, one can make a precise measure of metallicity despite the presence of aerosols, but more often the retrieved metallicity of a cloudy or hazy atmosphere has significantly lower precision than for a clear atmosphere with otherwise similar properties. Future efforts to securely link aerosol properties to atmospheric metallicity and temperature in a physically motivated manner will ultimately enable a robust physical understanding of the processes at play in cloudy, hazy exoplanet atmospheres.

Source Apportionment of Aerosol at a Coastal Site and Relationships with Precipitation Chemistry: A Case Study over the Southeast United States.

This study focuses on the long-term aerosol and precipitation chemistry measurements from colocated monitoring sites in Southern Florida between 2013 and 2018. A positive matrix factorization (PMF) model identified six potential emission sources impacting the study area. The PMF model solution yielded the following source concentration profiles: (i) combustion; (ii) fresh sea salt; (iii) aged sea salt; (iv) secondary sulfate; (v) shipping emissions; and (vi) dust. Based on these results, concentration-weighted trajectory maps were developed to identify sources contributing to the PMF factors. Monthly mean precipitation pH values ranged from 4.98 to 5.58, being positively related to crustal species and negatively related to SO42−. Sea salt dominated wet deposition volume-weighted concentrations year-round without much variability in its mass fraction in contrast to stronger seasonal changes in PM2.5 composition where fresh sea salt was far less influential. The highest mean annual deposition fluxes were attributed to Cl−, NO3−, SO42−, and Na+ between April and October. Nitrate is strongly correlated with dust constituents (unlike sea salt) in precipitation samples, indicative of efficient partitioning to dust. Interrelationships between precipitation chemistry and aerosol species based on long-term surface data provide insight into aerosol–cloud–precipitation interactions.

Analysis of aerosol optical depth over Bahrain and Eastern Province of Saudi Arabia based on MERRA-2 model

Spatial and temporal variability of aerosol optical depth (AOD) together with aerosol-type specification were analyzed over Eastern Province of Kingdom of Saudi Arabia (KSA) and Bahrain from 2008 to 2019. To investigate study region with more details, the Eastern Province of Saudi Arabia and Bahrain was divided into three and four zones, respectively. This work utilized comprehensive satellite-based air quality data using NASA’s Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) model. The retrieved total AOD data exhibited relatively lower average values in the Bahraini zones in comparison with the Eastern KSA during the study period. The monthly total AOD values in Bahraini zones were in the range of 0.20 and 0.87, while they were in the range of 0.23 and 0.91 in KSA zones. The AOD values were positively correlated with ambient air temperature (r = 0.43), while they were negatively correlated with relative humidity (r = 0.59) in Bahrain. Seasonal wind rose diagrams for Bahrain and monthly synoptic maps of (20–40°N, 40–60°E) West Asia region demonstrates that dominant wind direction is from NNW to Bahrain. The data assimilation algorithms in MERRA-2 showed that the major aerosol species that contributed to total AOD were as follows: mineral dust (68–74%), sulfate (17–20%), organic carbon (4–5%), sea salt (3–5%) and black carbon (2%). Monthly, seasonal and annual variations of speciated AOD values assisted in understanding aerosols loading over study area.

Comparison and evaluation of the simulated annual aerosol characteristics over China with two global aerosol models

In this study, simulations of the annual mean aerosol budget, aerosol optical properties, and surface mass concentration in 2006 in China are performed with two aerosol interactive global atmosphere models, namely, the Nonhydrostatic ICosahedral Atmospheric Model (NICAM) coupled with the Spectral Radiation Transport Model for Aerosol Species (SPRINTARS) and the Beijing Climate Center Atmospheric General Circulation Model (BCC_AGCM) coupled with the Canadian Aerosol Module (CAM) online. The observed and simulated aerosol optical depths (AODs) exhibit similar horizontal distributions with large values over eastern and central China, and sulfate aerosols contribute the main differences between the AODs simulated by NICAM and BCC_AGCM. The simulated sulfate and dust surface concentrations are more consistent with observations compared with the simulated carbonaceous surface concentrations, and both models can reproduce the decreasing tendency of the sulfate surface concentration from urban sites to rural sites. However, the dust emission and deposition levels in China simulated by BCC_AGCM are three times as high as those simulated by NICAM, and the major sink processes of the anthropogenic sulfate, black carbon (BC), and organic carbon (OC) aerosols over China are very different between the two models. The emission and deposition results, which are closely related to the model-assumed aerosol particle size distribution, indicate that the current aerosol size distribution used in the two models should be further improved. The differences in dust emission parameterizations also lead significant discrepancies in aerosol cycles and the dust emission scheme is an important factor determining the magnitudes of global and regional dust emission fluxes.

Roles of Sulfur Oxidation Pathways in the Variability in Stable Sulfur Isotopic Composition of Sulfate Aerosols at an Urban Site in Beijing, China

Sulfate (SO42–) is an important chemical species in atmospheric aerosols, which strongly impacts atmospheric chemistry processes and climate change. Stable sulfur isotopes (δ34S) of sulfate aerosol...

Aerosol Effective Radiative Forcing in the Online Aerosol Coupled CAS-FGOALS-f3-L Climate Model

The effective radiative forcing (ERF) of anthropogenic aerosol can be more representative of the eventual climate response than other radiative forcing. We incorporate aerosol–cloud interaction into the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System (CAS-FGOALS-f3-L) by coupling an existing aerosol module named the Spectral Radiation Transport Model for Aerosol Species (SPRINTARS) and quantified the ERF and its primary components (i.e., effective radiative forcing of aerosol-radiation interactions (ERFari) and aerosol-cloud interactions (ERFaci)) based on the protocol of current Coupled Model Intercomparison Project phase 6 (CMIP6). The spatial distribution of the shortwave ERFari and ERFaci in CAS-FGOALS-f3-L are comparable with that of most available CMIP6 models. The global mean 2014–1850 shortwave ERFari in CAS-FGOALS-f3-L (−0.27 W m−2) is close to the multi-model means in 4 available models (−0.29 W m−2), whereas the assessing shortwave ERFaci (−1.04 W m−2) and shortwave ERF (−1.36 W m−2) are slightly stronger than the multi-model means, illustrating that the CAS-FGOALS-f3-L can reproduce the aerosol radiation effect reasonably well. However, significant diversity exists in the ERF, especially in the dominated component ERFaci, implying that the uncertainty is still large.

Biofuel Burning Influences Refractory Black Carbon Concentrations in Seasonal Snow at Lower Elevations of the Dudh Koshi River Basin of Nepal

When deposited on snow and ice, light absorbing impurities (LAIs) such as dust and black carbon (BC) reduce surface albedo and enhance melt. BC comes from incomplete combustion of fossil fuels and biomass. Local and regional sources of BC exist in High Mountain Asia, such as dry-dung burning for heat and fuel, which occurs in close proximity to snow and glaciers. Local dust or dust transported from the Indo-Gangetic Plain is also present. In the Ganges River Basin, meltwater is dominated by seasonal snow, yet relatively few observations of impurities in seasonal snow exist. To understand sources of impurities and their concentrations for seasonal snow on land, we evaluated multiple lines of evidence to scale up from ground-based measurements in the Dudh Koshi River Basin, a remote headwater basin within the Khumbu Region of Nepal. We obtained ground-based in-situ observations of refractory black carbon (rBC) measured by Single Particle Soot Photometer (SP2), including size distributions in snow on land. We interpreted these results in the context of concurrent Moderate Imaging Spectroradiometer (MODIS) satellite observations and speciated aerosol optical depth derived from reanalysis products modeled with the Navy Aerosol Analysis Prediction System (NAAPS) global aerosol model. We collected snow samples, mostly in the Gokyo Valley, at varying distances from local tea houses along a 2000 meters above sea level (m.a.s.l) elevation transect from 3250 to 5299 m.a.s.l . rBC concentrations ranged from 3.9 to 76.8 µg-rBC/L-H2O. Although previous data do not exist at these lower elevations, our findings are higher than previous surface snow results at higher elevations in the nearby Khumbu Valley. In general, rBC concentrations were lower in fresh snow than aged snow; concurrent MODIS satellite observations of snow albedo also show smaller impacts from LAIs in visible wavelengths in fresh snow. rBC decreased with elevation in aged snow samples, as did concurrent MODIS albedo observations. rBC-particle size distributions also shifted to a larger mode for aged snow samples. Results from NAAPS indicate anthropogenic and biogenic fine aerosols from biofuel (dry-dung burning) are primary aerosol species for the study period, at ~thrice the concentration of dust and smoke.

Comparison of V4 and V3 CALIOP (L3) aerosol products: A global perspective

Gridded satellite products provide (computationally less-intense) opportunities to compare and contrast parameters from different versions/sensors. In the present study, Level-3 (L3) Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol products from the most recent release (version 4, V4) are compared with its earlier version (version 3, V3) products. The various improvements in V4 are detailed and the resultant changes in aerosol optical depth (AOD) and aerosol vertical extinction profiles for various aerosol species (total aerosol, dust, polluted dust, smoke) over various regions are discussed. Broadly, V4 global AOD is higher than the V3 AOD (except for polluted dust). Significant differences in V4 and V3 AODs are observed over Africa, East Asia, Atlantic Ocean, Arabian Sea, Bay of Bengal and South America. Seasonal-wise global mean percentage difference in V4 and V3 total-AODs (with respect to V4 AODs) ranged between 9% and 15%. The change in the spatial distribution of polluted dust over oceanic regions is one of the significant differences between V4 and V3. V4 total-AODs are closer to Moderate Resolution Imaging Spectroradiometer (MODIS) AODs than V3 total-AODs are. The shape of the aerosol extinction profiles also differed between V4 and V3. The altitudinal differences in the V4 and V3 extinction values varied spatio-temporally.

Changes in ammonia and its effects on PM2.5 chemical property in three winter seasons in Beijing, China

NH3, SO2, NOx and the inorganic ions of PM2.5 in winter 2009, 2014 and 2016 were examined to investigate the change in NH3 and aerosol chemistry in Beijing, China. NH3 concentrations showed an increase by 59% on average, in contrast to the decrease of SO2 by 63% from winter 2009 to 2016. The mean mass ratio of NH3/NHx was 0.83 ± 0.12 in 2016, which is higher than those obtained in 2009 and 2014, implying more NHx remaining as free NH3 in 2016 winter. Our findings suggest that vehicles exhaust emissions are an important NH3 source in urban central atmosphere of Beijing in winter. Despite the observed NOx presenting declining trends from 2014 to 2016, nitrate concentrations even exhibited a significant increasing trend, which may be largely attributable to high NH3 levels. An in-depth analysis of measured NH3 and aerosol species in a heavy pollution episode in December 2016, combined with the acidity predicted by ISORROPIA II model demonstrated abundant NH3 most of the time in air, where NH3 is not only a precursor for NH4+ but also effect the neutralization of SO42− and NO3− in PM2.5. With high RH and low photochemical activity, elevated NO3− concentration was attributed to an enhanced heterogeneous conversion of NOx to HNO3 to form NH4NO3 in pollution transport stage. The decrease in NOx from high level and the increase in NH3, with peaks of SO42− occurring were observed in pollution cumulative stage. The aqueous-phase oxidation of SO2 by NO2 to sulfate might play an important role with high pH values. Our results suggested that the simultaneous control of NH3 emissions in conjunction with SO2 and NOx emissions would be more effective in reducing particulate matter PM2.5 formation.