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The vertical structure of aerosols plays an important role in regional air pollution and climate change. Using long-term data on aerosol optical properties obtained through satellite observations (MODIS/Terra, MODIS/Aqua, CALIOP) and reanalysis products (CAMS) during 2007–2021, we analysed the seasonal evolution and vertical distribution of aerosol loading in northeastern China (NEC). We also analysed the seasonal variation trends of aerosol optical depth (AOD) of aerosol species. The AODs during spring and summer were high and distributed in Liaoning (LN) with an average value of approximately 0.6, which was higher in central Jilin and southern Heilongjiang. Sulfate AOD (AOD_SO 4) and organic matter AOD (AOD_OM) in NEC were higher during spring and summer (approximately 0.2), and the maximum value of dust AOD (AOD_DU) was approximately 0.1 obtained for western LN. During spring, the aerosol extinction coefficient (AEC) for NEC was high at heights below 2.0 km in LN, and its value was maximum (approximately 0.16 km−1) near the ground in LN during winter. The AEC was concentrated within 0–1 km during winter and higher within 1–3 km during spring and summer in NEC. During 2007–2021, AOD exhibited a decreasing trend, with higher average AOD during spring and summer and lower average AOD during autumn and winter. The seasonal trend of AOD in NEC exhibited a decreasing trend. BC_AOD showed the largest decline in spring, followed by DU_AOD and OM_AOD, and SO4_AOD showed a significant decline in summer. This paper presents accurate information on regional types and vertical distribution of aerosols. This information can be used for model improvement and satellite validation. [Display omitted] • AOD_SO4 was higher in summer, and AOD_OM was larger during spring in radial. • The annual decreased aerosol extinction was vertically distributed within 0–3 km. • Type-dependent seasonal AOD exhibited an interannual decreasing trend in NEC. [ABSTRACT FROM AUTHOR]

Aerosol loading and properties have an important influence on the radiative effect of aerosols and regional climate change. Based on the long-term datasets of aerosol optical products retrieved from multiple satellite observations (MODIS/Terra, MODIS/Aqua, MISR, and CALIOP/CALIPSO) and a reanalysis product (CAMS) from 2007 to 2019, the climatology and interannual variability in total aerosol optical depth (AOD) and type-dependent AODs related to aerosol particle properties and components over southwest China (SWC) and northern India (NI) are investigated, and the vertical distribution of type-dependent aerosol extinctions are also examined. Overall, consistent spatial distribution characteristics of the AOD climatology are captured across the different datasets, albeit with slight differences in magnitude. Multi-year mean high AODs are mainly concentrated in areas such as the Sichuan Basin (SCB) (∼0.5) and NI (∼0.6), dominated by anthropogenic aerosols, and the Tarim Basin (∼0.5), dominated by mineral dust aerosols. In contrast, the central Tibetan Plateau (CTP) area, with a relatively clean background, has a lower AOD (∼0.1) on a multi-year average basis. When the total AOD is separated by chemical components, the CAMS reanalysis demonstrates that sulfate and carbonaceous aerosols (CAs) contribute nearly equally to AOD in SCB, while CAs is the largest contributor to the high aerosol loading in NI. An enhanced vertical aerosol extinction coefficient (AEC) is mainly located below 1 km in both SCB and NI, reaching 0.35 km−1 and 0.55 km−1. In CTP, the AEC has two peaks (∼0.02 km−1) at 2.5 km and 3.5 km. By partitioning the column AOD by different altitude ranges, we find that about 73.8% (80.6%) of the AOD in SCB (NI) is located in the lower troposphere (0–2 km). The resulting trend analyses show that a significant decreasing (increasing) trend (P < 0.05) in AOD in SCB (NI) is accurately captured by both the satellite products and the CAMS reanalysis. In contrast, a significant decline (P < 0.1) in the CTP region is observed in CAMS only, while a non-significant decline is detected in the satellite products. The results of this study have potential implications for understanding the vertical distribution and interannual variability of regional aerosol loading. • Climatology of type-dependent AODs over SWC and NI were presented. • Sulfate and CAs contribute nearly equally to AOD in SCB. • CAs is the largest contributor to the high aerosol loading in NI. • About 73.8% (80.6%) of the AOD in SCB (NI) is located within 0–2 km. • A significant decreasing (increasing) AOD trend in SCB (NI) is captured. [ABSTRACT FROM AUTHOR]

Aerosol generated from the economic development and extensive urbanization in northeast China (NEC) could influence aerosol optical properties and affect the regional air quality. The level 3 aerosol optical depth (AOD) of different particle size and shape (spherical or nonspherical) obtained by Multiangle Imaging Spectroradiometer (MISR) version 23 were used to estimate their seasonal, annual, and decadal distribution and contribution in NEC from 2001 to 2018. The highest AOD of approximately 0.3 was found in the central Liaoning urban agglomeration, and the lowest AOD occurred in the mountainous area of NEC; the proportion of spherical AOD in NEC region was more than 90%. The contribution of large AOD was higher in spring, ranging from 28.8% to 29.8%. In spring and summer, small and medium AODs were concentrated in central Liaoning (approximately 0.2–0.3 and 0.06–0.08, respectively). The annual variation in the AOD of different particle size was significantly higher in Liaoning than in Jilin and Heilongjiang. The annual proportions of small and spherical AODs were approximately 60% and 90%, respectively. The annual occurrence of clean conditions with AOD < 0.05 was most common in northern Heilongjiang (approximately 20%). In NEC, the annual occurrence frequencies of 0.05 < AOD < 0.15 and AOD > 0.6 were the highest (approximately 50%) and the lowest (less than 1%), respectively. Interdecadal AOD revealed a positive trend from 2001 to 2008 and a negative trend from 2009 to 2018. The frequency of occurrence trend at different AOD levels also changed from positive to negative between these two periods. The findings in this study are based on the first aerosol retrieval of the newly released MISR in NEC. The results provide a comprehensive understanding of the regional and climatological aerosol extinction with different AOD of size and shape as well as various level bins in NEC. Unlabelled Image • Larger contribution of small size and spherical AOD was found in NEC. • Occurrence frequency was highest for 0.05 < AOD < 0.15 (about 50%) in NEC. • Interdecadal AOD and frequency changed from positive to negative in 2008. [ABSTRACT FROM AUTHOR]

Different types of aerosols play a crucial role in the climate system according to their vertical distributions and optical-radiative properties. Southwest China (SWC), consisting of the Sichuan Basin (SCB), the Yunnan-Guizhou Plateau (YGP) and the Tibetan Plateau (TP), is one of the most topographically complex regions in the world and is also facing varying degrees of air pollution problems caused by local, high-intensity anthropogenic emissions and trans-regional transport of aerosols from surrounding areas. However, a comprehensive understanding of the regional three-dimensional (3D) characteristics of aerosol distribution and evolution over SWC has not to be achieved yet. Here, the seasonal distributions and vertical structures of four types of aerosols, including dust, polluted continental/smoke, polluted dust and elevated smoke, were detected by using the quality controlled CALIPSO Level 2 nighttime aerosol profile product from 2007 to 2016 in this study. The loading of aerosols over the SCB was higher than that over the other regions, and of the sources, polluted continental/smoke and polluted dust, related to anthropogenic sources, contributed the most to the aerosols. However, we also found that polluted continental/smoke and polluted dust have declined since 2013, which was due to the strict regulatory measures implemented for industry emissions and biomass burning in agriculture in recent years. The elevated smoke aerosols over the YGP at an altitude of 3 km in spring were significantly higher than those in other seasons, while the polluted continental/smoke aerosols at an altitude of 1–2 km were higher in autumn and winter than in the other seasons and was considered to be from local biomass burning. The aerosol optical depth (AOD) over the TP was nearly one magnitude lower than that over the other two regions. However, either the dust or polluted continental/smoke from the Qaidam Basin or elevated smoke elevated from the Indo-Gangetic Basin could have been transported to the layer as high as 6 km over the TP. Additionally, the heights of the highest frequencies of AOD for all types of aerosols for the SCB, YGP and TP were 0–2 km, 2–4 km and 4–6 km, respectively. In summer, elevated smoke can rise to heights of 8–10 km on the TP. The results of this study provide an observational basis for further understanding the trans-regional transport of aerosols and their climate effects in SWC. • 3D vertical structure of aerosols over SWC were presented during 2006–2016. • Polluted aerosols over SWC have declined since 2013. • Smoke aerosols are mainly from local emissions and trans-regional transport. • Elevated smoke can rise to heights of 8–10 km over the TP in summer. [ABSTRACT FROM AUTHOR]

Northeast China has undergone rapid urbanisation with increased anthropogenic emissions, and the types and absorption properties of aerosols may affect regional climate change. MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2) distributions of aerosol optical depth (AOD), Ångström exponent (AE), and absorption aerosol optical depth (AAOD) from 1980 to 2017 was studied to estimate the climatology of aerosol optical properties over Northeast China. The highest AOD and AAOD occurred in Liaoning Province range from 0.3 to 0.4 and 0.02–0.03, respectively. The spacial distribution of black carbon (BC) AOD was similar to AAOD with maximum value in Liaoning province about 0.04 related to the emission sources and human activities. The seasonal interdecadal distribution indicated larger dust (DU) AOD in Liaoning (0.12) and organic carbon (OC) AOD in Heilongjiang (0.18). The contribution of SO 4 to total AOD was significant in autumn and winter, and BC particles contributed 70% to total AAOD in all seasons. The decadal change in AOD was positive for 2000–2009 (0.2/decadal) due to the increased dust events happening in spring. The positive correlation between AOD and relative humidity (RH) at surface was about 0.4–0.6; the negative correlation between AOD and surface wind speed (WS) (−0.6), planetary boundary layer height (PBLH) (−0.2 to −0.6), sea level pressure (SLP) (−0.2) was found over the study period. This study's findings enable more comprehensive understanding of the distribution of aerosols optical properties and regional climatology in Northeast China. • Higher interdecadal AOD andAAOD wereobviouslyfound in Liaoning Province. • The contribution of SO4 and BC was significantto total AOD and AAOD. • Meteorological factors havelarge influence on regional aerosol extinction. [ABSTRACT FROM AUTHOR]