The seasonal and spatial variations of vertical distribution and optical properties of aerosols over China are studied using long-term satellite observations from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) and ground-based lidar observations and Aerosol Robotic Network (AERONET) data. The CALIOP products are validated using the ground-based lidar measurements at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). The Taklamakan Desert and Tibetan Plateau regions exhibit the highest depolarization and color ratios because of the natural dust origin, whereas the North China Plain, Sichuan Basin and Yangtze River Delta show the lowest depolarization and color ratios because of aerosols from secondary formation of the anthropogenic origin. Certain regions, such as the North China Plain in spring and the Loess Plateau in winter, show intermediate depolarization and color ratios because of mixed dust and anthropogenic aerosols. In the Pearl River Delta region, the depolarization and color ratios are similar to but higher than those of the other polluted regions because of combined anthropogenic and marine aerosols. Long-range transport of dust in the middle and upper troposphere in spring is well captured by the CALIOP observations. The seasonal variations in the aerosol vertical distributions reveal efficient transport of aerosols from the atmospheric boundary layer to the free troposphere because of summertime convective mixing. The aerosol extinction lapse rates in autumn and winter are more positive than those in spring and summer, indicating trapped aerosols within the boundary layer because of stabler meteorological conditions. More than 80 % of the column aerosols are distributed within 1.5 km above the ground in winter, when the aerosol extinction lapse rate exhibits a maximum seasonal average in all study regions except for the Tibetan Plateau. The aerosol extinction lapse rates in the polluted regions are higher than those of the less polluted regions, indicating a stabilized atmosphere due to absorptive aerosols in the polluted regions. Our results reveal that the satellite and ground-based remote-sensing measurements provide the key information on the long-term seasonal and spatial variations in the aerosol vertical distribution and optical properties, regional aerosol types, long-range transport and atmospheric stability, which can be utilized to more precisely assess the direct and indirect aerosol effects on weather and climate.

The particle mixing state plays a significant yet poorly quantified role in aerosol radiative forcing, especially for the mixing of dust (mineral absorbing) and anthropogenic pollution (black carbon absorbing) over East Asia. We have investigated the absorption enhancement of mixed-type aerosols over East Asia by using the Aerosol Robotic Network observations and radiative transfer model calculations. The mixed-type aerosols exhibit significantly enhanced absorbing ability than the corresponding unmixed dust and anthropogenic aerosols, as revealed in the spectral behavior of absorbing aerosol optical depth, single scattering albedo, and imaginary refractive index. The aerosol radiative efficiencies for the dust, mixed-type, and anthropogenic aerosols are −101.0, −112.9, and −98.3 Wm${}^{-\mathrm{2}}{\mathit{\tau }}^{-\mathrm{1}}$ at the bottom of the atmosphere (BOA); −42.3, −22.5, and −39.8 Wm${}^{-\mathrm{2}}{\mathit{\tau }}^{-\mathrm{1}}$ at the top of the atmosphere (TOA); and 58.7, 90.3, and 58.5 Wm${}^{-\mathrm{2}}{\mathit{\tau }}^{-\mathrm{1}}$ in the atmosphere (ATM), respectively. The BOA cooling and ATM heating efficiencies of the mixed-type aerosols are significantly higher than those of the unmixed aerosol types over the East Asia region, resulting in atmospheric stabilization. In addition, the mixed-type aerosols correspond to a lower TOA cooling efficiency, indicating that the cooling effect by the corresponding individual aerosol components is partially counteracted. We conclude that the interaction between dust and anthropogenic pollution not only represents a viable aerosol formation pathway but also results in unfavorable dispersion conditions, both exacerbating the regional air pollution in East Asia. Our results highlight the necessity to accurately account for the mixing state of aerosols in atmospheric models over East Asia in order to better understand the formation mechanism for regional air pollution and to assess its impacts on human health, weather, and climate.

The formation mechanisms of particulate pollution in Lanzhou, which used to be one of the most polluted cities across the world, remain unclear even though air pollution in Lanzhou has been improved in recent decades. Multiple online data during 2019–2020 winter was used to analyze the characteristics and reveal the formation mechanisms of particulate pollution in Lanzhou. Organic matter, nitrate, sulfate, and ammonium accounted for 35.8%, 16.6%, 12.7%, and 10.8%, respectively, of PM_2.5 mass. The contribution of secondary inorganic aerosols decreased from low to high particulate levels. Nitrate and ammonium concentrations consistently increased with increasing PM_2.5 while sulfate concentrations firstly increased but remained stagnant under high particulate conditions. The sulfur and nitrogen oxidation ratios exhibited relatively low values of 0.18 ± 0.12 and 0.11 ± 0.05, respectively. Nitrogen oxidation ratio showed little dependence on relative humidity because of limited aqueous phase generation of nitrate. The increasing nitrate to sulfate ratio and decreasing organic carbon to elemental carbon ratio under high particulate concentrations indicate relative decreasing contribution of coal burning and increasing contribution of vehicle exhaust emissions on particulate pollution. The rapid decreasing trend of secondary organic carbon to elemental carbon ratio under high particulate concentrations was attributed to a combination of the relatively decreasing photochemical generations and increasing accumulation of primary emissions by the weakened atmospheric diffusion ability. Our results suggest that controlling primary carbonaceous species and vehicle exhaust emissions is the most effective measure in order to sustainably mitigate particulate pollution in Lanzhou in the future.