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Aerosol types have crucial and distinguished impacts on climate effects and cause the difference of air pollution. However, direct retrieval of aerosol type by satellite remote sensing is difficult, and the satellite products of aerosol type are seriously lacking. At present, the identification of aerosol type is mainly based on ground-based observation data, but the coverage area of ground-based stations is limited, and large-scale spatial continuous monitoring cannot be carried out. The existing aerosol type identification methods based on satellite data need to combine multiple satellites data (e.g. Moderate-resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), etc.) which leads to a low temporal resolution. The research about aerosol type identification only based on geostationary satellite data is lacking. Therefore, aerosol type identification based on the multi-parameter threshold method and the neural network method are proposed and compared in this paper. The neural network jointly using spectral and temporal information was trained and tested by the measurements from 26 sites of Aerosol Robotic Network (AERONET) and Sun-Sky Radiometer Observation Network (SONET). For the overall validation, the aerosol type identification based on the neural network is better than that based on the multi-parameter threshold method, and the accuracy reaches 71.44%. Atmospheric environment monitoring and quantitative remote sensing can be supported by this study. • Aerosol type, neural network, geostationary satellite [ABSTRACT FROM AUTHOR]

For regions where limited in-situ observations are available for use as a reference, such as in China, the understanding of how changes in the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol retrieval algorithm impact the data quality is limited. In this paper, the MODIS-Aqua Aerosol Optical Thickness (AOT) Collection 5 (C5) and 6 (C6) Dark-Target (DT) products are evaluated by comparison with similar products from the China Aerosol Remote Sensing NETwork (CARSNET) and the Aerosol Robotic Network (AERONET) in China for the year 2008. The validation data are analyzed for key factors affecting the results of the MODIS-DT aerosol retrieval algorithm, including surface type, aerosol loading and aerosol absorption. The impacts of the change from the C5 to the C6 versions of the MODIS AOT retrieval algorithm are discussed in detail. The main findings are: (1) The agreement from retrieval aspects between both MODIS C5/C6 and CARSNET-AERONET for most AOT values over distinct regions indicates that the conclusions obtained from C5 hold for C6; (2) MODIS-DT has an extended coverage (more retrievals) with good quality due to the change of upstream data (calibration, cloud masking, etc); (3) About 64% of the MODISDT C6 AOT data over China fall within the (±0.15 AOT ± 0.05) error envelope; (4) positive AOT differences between C6 and C5 over relatively dark surfaces and negative differences over relatively bright surfaces due to the change of surface parameterization have been observed; (5) the AOT difference between MODIS and CARSNET-AERONET relating to AOT loading is not significant, especially for large AOT; (6) MODIS-DT performs well for absorbing aerosol over relatively bright surfaces. • MODIS/Aqua AOT C5/C6 DT products are evaluated to understand the effects of different parameters on algorithm performance. • Both MODIS C5 and C6 DT show good quality over China under different surface and atmospheric conditions. • MODIS C6 DT aerosol product has an extended coverage with good quality over China. [ABSTRACT FROM AUTHOR]

Understanding the uncertainty of satellite aerosol products for different surface types is very important for algorithm optimization and related applications. Ground-based aerosol observations provided by AERONET are most often used to validate satellite aerosol products. However, AERONET ground-based sites are unevenly distributed in China, mainly concentrated in urban areas, with few sites in other surface types, leading to limitations in evaluating the accuracy of products for different surface types. To address this issue, the National Civil Space Infrastructure Satellite Aerosol Product Validation Network (SIAVNET) is constructed to complement ground-based aerosol observations for multiple surface types in China and support the validation research of satellite aerosol products. The main purpose of this paper is to introduce SIAVNET and analyze the supplementary role it plays in the validation of satellite aerosol products for different surface types in China. Firstly, this study introduces the supplementation of SIAVNET to ground-based observations in different surface types. SIAVNET supplements 21 sites with multiple surface types, mainly supplementing vegetated areas, with 17 sites. In particular, SIAVNET places a site in bare land, which fills the gap of ground-based observation for bare land. Then, to further demonstrate the supplemental value of SIAVNET observation in the validation of satellite aerosol products, the accuracy of MODIS aerosol products with four different resolutions (i.e., 1 km, 3 km, 10 km, and 1°) for different surface types in China is evaluated using all ground-based observations. For bare land, the accuracy of different resolution products is obtained based on SIAVNET observations, with 50.91%–69.23% of the retrievals falling within the expected error, which fills the validation gap for bare land. For vegetated areas, compared to the AERONET-only based products evaluation, the use of SIAVNET significantly affects the validation results in grassland for the 3 km and 10 km products, with the proportion of retrievals falling within the expected error decreasing from 78.61%, 74.30% to 64.16% and 63.17%, failing to reach satisfactory levels (66%). For urban areas, supplemental SIAVNET observations have almost no effect on the validation results for the different aerosol products obtained based on AERONET. These results are expected to provide guidance for detailed satellite aerosol product validation over China using SIAVNET data. • SIAVNET complements the 21 sites with multiple surface types, especially filling the gap of observations in bare land. • By using the SIAVNET data, the accuracy of aerosol products over China is obtained. • The supplement of SAVNET-China data significantly influences the validation results of 3 km and 10 km products in grassland. [ABSTRACT FROM AUTHOR]

The Directional Polarimetric Camera (DPC) is the first Chinese satellite-borne multi-angle polarimetric sensor onboard the GaoFen-5 (GF-5) satellite, which was launched on May 9th 2018. In this paper, we present the spatiotemporal variability of satellite-measured aerosol components (such as, black carbon, brown carbon, iron oxides contained in mineral dust etc.) over North China Plain (36–41°N, 113–123°E) for a heavily haze-polluted case, to demonstrate the first successful retrievals of aerosol component content and optical property directly from the DPC/GF-5 instrument measurements. We also reveal the relationship between absorbing/scattering component mass ratio and aerosol absorption based on the multi-angle polarimetric satellite measurements, which presents comparable agreement with previous laboratory studies and field studies for an indirect validation of aerosol component retrievals. In addition, the feasibility, stability and uncertainty of the aerosol optical property and component content retrievals from DPC multi-angle polarimetric observations were evaluated and assessed by sensitivity tests. The distributions of DPC/GF-5 aerosol optical depth (AOD) are in line with satellite-observed MODIS (Moderate-resolution Imaging Spectroradiometer) AOD and ground-based CARSNET (China Aerosol Remote Sensing Network) AOD products. Therefore, the multi-angle polarimetric satellite measurements show an encouraging potential for the comprehensive inversion of aerosol optical, microphysical and chemical properties. The results and further applications of this component algorithm in the future are helpful to reduce the uncertainty of climate change assessment by providing the measurements of aerosol component, in particular for black carbon, brown carbon, and iron oxides contained in dust, with large and extensive spatiotemporal scale. [Display omitted] • We propose a new aerosol retrieval application to multiangle polarimetric observation. • The first successful retrieval of aerosol component content from DPC is presented. • Satellite-measured BC, BrC and iron oxides are characterized in a haze-polluted case. • We reveal the link of satellite-measured absorbing/scattering component ratio to AAE. [ABSTRACT FROM AUTHOR]

Based on the principle of light propagation, it is necessary to obtain the ratio (R MN) of atmospheric aerosol mass concentration to the imaginary part of the atmospheric equivalent refractive index for measuring aerosol mass vertical flux. In this paper, the factors affecting the R MN values are analyzed by numerical calculation under an ideal state and by using observational data. Numerical calculations show that the R MN is mainly determined by the aerosol particle size distribution (PSD), hygroscopicity parameters and relative humidity. With the same relative humidity, the smaller the geometric mean diameter (Dg) is, the larger the R MN , and when the aerosol particle hygroscopicity parameter is greater than 0.14, the greater the relative humidity is, the smaller the R MN. Comprehensive experiments were conducted in urban Hefei, and the results of observations at Hefei confirm the numerical results. Data from ten cities across China also confirm the numerical results. The order of geometric mean diameter of aerosol particles at the ten sites can be determined by the order of R MN , and the order of hygroscopicity parameters at the ten sites can be determined by the order of the change rate of R MN with relative humidity. The geometric mean diameters of aerosol particles are different among the ten sites, while the hygroscopicity parameters are similar. • The ratio (R MN) of TSP mass concentration to the imaginary part of the atmospheric equivalent refractive index is defined • The R MN is mainly affected by aerosol particle size distribution, relative humidity and hygroscopicity parameter. • The order of geometric mean diameter of aerosol particles at the ten sites can be determined by the order of R MN. • The variation of R MN with relative humidity reflects hygroscopicity parameter (α) of the aerosol particles. [ABSTRACT FROM AUTHOR]

Abstract: Size distributions can provide important information about aerosol sources, formation, and growth mechanisms. However, compared to size distributions of inorganic aerosols, size distributions of carbonaceous aerosols have been much less studied and reported in the literature. In this paper, we systematically measured size distributions of elemental carbon (EC), organic carbon (OC), oxalate, polycyclic aromatic hydrocarbons (PAHs), as well as major inorganic ions in urban aerosols in Shenzhen, China. Totally 24 sets of samples were collected using a ten-stage micro orifice uniform deposit impactor (MOUDI) during October 2009 to February 2010. Three lognormal modes contained in the size distributions of species were resolved based on positive matrix factorization (PMF) analysis of the measured dataset, corresponding to the condensation (peak=0.34μm), droplet (peak=0.84μm), and coarse (peak=5.4μm) modes, respectively. The mean concentrations of EC in the condensation, droplet, and coarse modes were 2.20, 1.18, and 0.64μgm−3, respectively, and the modal characteristics of EC indicate that fresher local combustion emissions contributed mostly to aerosol EC in the urban atmosphere of Shenzhen. The mean concentrations of OC in the condensation, droplet, and coarse modes were 2.29, 3.34, and 3.51μgm−3, respectively, and the modal characteristics of OC indicate that its sources were more primary in the condensation mode while more secondary in the droplet mode. The modal characteristics of aerosol oxalate and PAHs suggest that they were predominantly from in-cloud secondary formation and local emissions, respectively. [Copyright &y& Elsevier]

Abstract: A seven-year analysis of clear-sky column-integrated aerosol optical properties and direct radiative forcing at Gosan in Korea is presented in this paper; the Gosan site is heavily impacted by aerosols emitted from the Asian continent. MODIS and AERONET Sun/sky radiometer measurements showed significant seasonal and geographical variability in aerosol optical depth (AOD), with high AODs over the east coastal industrialized regions of China in spring and summer. At the Gosan site, the monthly mean AOD at 675nm ranged between 0.12 and 0.36. High AODs were observed from April to June (>0.33), while low-to-moderate monthly mean AODs were apparent during the remaining months. The single scattering albedo (SSA) exhibited relatively low values from February to May (<0.93), indicating the presence of light-absorbing aerosols, whereas high values of SSA (>0.93) were observed during the remaining months. The annual average clear-sky direct forcing (forcing efficiency) at the surface was −27.55±9.21W m−2 (−91.85±11.12W m−2 τ −1) and at the top of the atmosphere (TOA) was −15.79±4.44W m−2 (−53.76±6.70W m−2 τ −1), thereby leading to an atmospheric absorption of 11.76±5.82W m−2. From March to June, the surface aerosol radiative forcing (forcing efficiency) ranged between −27.29 (–85.33) and −34.76W m−2 (−97.19W m−2 τ −1), whereas at TOA it ranged between −16.84 (−51.82) and −19.10W m−2 (−56.05W m−2 τ −1), and the atmospheric forcing ranged between 10.45 and 16.41W m−2. The atmospheric forcing (i.e., atmospheric absorption) caused an increase in atmospheric heating (about 1.5 to 3.0K day−1). The strongest radiative heating was observed from April to May (>2.5K day−1). [Copyright &y& Elsevier]

Aerosol is a critical trace component of the atmosphere. Many processes in the Earth's climate system are intimately related to aerosols via their direct and indirect radiative effects. Aerosol effects are not limited to these climatic aspects, however. They are also closely related to human health, photosynthesis, new energy, etc., which makes aerosol a central focus in many research fields. A fundamental requirement for improving our understanding of the diverse aerosol effects is to accumulate high-quality aerosol data by various measurement techniques. Sunphotometer remote sensing is one of the techniques that has been playing an increasingly important role in characterizing aerosols across the world. Much progress has been made on this aspect in China during the past decade, which is the work reviewed in this paper. Three sunphotometer networks have been established to provide high-quality observations of long-term aerosol optical properties across the country. Using this valuable dataset, our understanding of spatiotemporal variability and long-term trends of aerosol optical properties has been much improved. The radiative effects of aerosols both at the bottom and at the top of the atmosphere are comprehensively assessed. Substantial warming of the atmosphere by aerosol absorption is revealed. The long-range transport of dust from the Taklimakan Desert in Northwest China and anthropogenic aerosols from South Asia to the Tibetan Plateau is characterized based on ground-based and satellite remote sensing as well as model simulations. Effective methods to estimate chemical compositions from sunphotometer aerosol products are developed. Dozens of satellite and model aerosol products are validated, shedding new light on how to improve these products. These advances improve our understanding of the critical role played by aerosols in both the climate and environment. Finally, a perspective on future research is presented. • Development of ground-based sunphotometer networks in China is presented. • Advances in our understanding of aerosol optical properties and radiative effects are reviewed. • A perspective on possible directions for future research is discussed. [ABSTRACT FROM AUTHOR]

China experienced heavy aerosol pollution in recent years. The aerosol pollution changes surface solar radiation and affects the land terrestrial carbon and water cycles in China. However, there are still some uncertainties in evaluating aerosol effects on ecosystem. Therefore, we combined the MODIS Atmosphere and Land products with process-based model to examine the sensitivity of gross primary productivity (GPP) and water use efficiency (WUE) to AOD. We also evaluated the effects of aerosol loadings on GPP and WUE at China FLUX sites from 2002 to 2015. Our results indicated that the radiative effects of aerosols on GPP varied with the vegetation type, which is consistent with other studies. Aerosol enhances the GPP by 2% in forest and reduces the GPP by 7% in grass land during the study period. We also found that the radiative effects of aerosols on WUE varied with the vegetation type. The WUE was promoted by the aerosols for all surface types when AOD is lower than 2.3. This indicates that the aerosol could enhance the plants WUE in most cases. Cloud during the study period restrains aerosol effects on growth of plants and improves the aerosol effects on WUE. Aerosol loadings during the study period fertilized the growth in two forest growth and slightly impede the growth of grass. They also improve the WUE for all vegetation types. The WUE increases more that 4% in most of sites increases. The results in this paper could help to fully understand the influences of aerosol on land carbon and water cycle. • MODIS products and BESS model were used to evaluate aerosol effects on GPP and WUE. • Aerosol enhances the GPP by 2% in forest during the study period. • The WUE increases more than 4% in most of sites due to the aerosol effects. • Cloud restrains aerosol effects on GPP and improves aerosol effects on WUE. [ABSTRACT FROM AUTHOR]

Substantial mitigation of air pollutants emissions has been performed since 2013 around Beijing, and changes in the atmospheric characteristics have been expected over the downstream area of Beijing. In this study, both WRF-Chem simulation and on-site measurements were utilized for the Baengnyeong (island) supersite, one of the representative regional background sites located in the Yellow Sea, the entrance area of the long-range transport process in Korea. The changes in the chemical compositions of inorganic aerosols were examined for spring-time during the Chinese emission mitigation period from 2014 to 2016. The measured ratio of ionic species to PM 2.5 at the Baengnyeong supersite showed changes in aerosol inorganic chemical compositions from sulfate in 2014 to nitrate in 2015–2016. The modeling results also showed that nitrate was low in 2014 and significantly increased in 2015 and 2016, and the acidic aerosol condition had also changed toward a more neutralized status in both the simulation and the observations. The WRF-Chem modeling study further indicated that the sulfur was not neutralized in 2014. However, in 2015 and 2016, SO 2 was more sufficiently neutralized as sulfur emissions were substantially reduced in China, while at the same time nitrate had begun to increase in such a 'SO 2 –poor' condition in Beijing area in China, and thus approaching more enhanced neutralization over the Yellow Sea area. The causes of the higher nitrate based on the modeled characteristics of the ammonia-sulfate-nitrate aerosol formation in response to the SO 2 emissions reduction in China are also discussed in this paper. Inorganic composition is changing from sulfate to nitrate, and aerosol acidity is approaching more enhanced neutralization over regional background area in Northeast Asia. Unlabelled Image • Inorganic components were examined over background area during Beijing's emission reduction. • Observations showed significant change in decreased sulfate and opposite trend in nitrate. • Aerosol acidity changed to enhanced nitrate neutralization through the emission reduction period. • More enhanced nitrate was also simulated by WRF-Chem mainly due to Beijing's emission mitigation. [ABSTRACT FROM AUTHOR]

Dust aerosols play an important role in climate change, however, the annual emissions simulated from dusty weather and dust devils are largely underestimated than observed, possibly due to the lack of gust on dust emission contribution under stationary weather conditions. This study estimates the gust emission by the use of 1-year measurements of 10-min wind speed from two field sites in Dunhuang (sandy desert) and Yumen (gravel desert) in northwestern China, and the concurrent estimations of dusty weather and dust devils are examined as well. The results show that: 1) about 25% of gust could contribute to dust emission throughout the year regardless in Dunhuang or Yumen. 2) Three dust processes have diverse occurrence times and intensities, i.e. gust could occur at any time with fiercer fluctuation in dust emission than dust devils and dusty weather which mainly occur between April and September and in spring, respectively. 3) During the non-dusty seasons, both dust devils and gust are prominent with gust overwhelmingly contributing the most, while during the dusty season when three mechanisms co-exists, dusty weather outperforms the others in Dunhuang, but takes a relatively even share of around 33% as the other two in Yumen. 4) On an annual scale, gust is the highest and second-highest contributor to the annual total dust emissions in Yumen and Dunhuang, respectively. This study not only highlights the nonnegligible contributor/mechanism of gust to dust emission, complementing the existing emission mechanisms to form a complete dust emission mechanism system, but also sheds light on a new perspective explaining the largely underestimated dust aerosols that are significant in the assessment of climate effects. • Significant diurnal, monthly and seasonal variability of gust emission. • Gust emission occurs randomly with the fiercest fluctuations. • Gust emission is overwhelmingly dominant during the non-dusty season. • 18.5– 50.4% of annual total dust emission is from gust in sandy deserts and Gobi. • Wind gust is an important and new dust emission mechanism. [ABSTRACT FROM AUTHOR]