Abstract
Abstract. 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.
Highlights
Atmospheric aerosols affect the radiative budget of the Earth–atmosphere system by direct interaction with solar radiation through scattering and absorption (Boucher et al, 2013)
A comparison of the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) observations with the Moderate-resolution Imaging Spectroradiometer (MODIS) products suggests that the CALIOP version 3 products provide a consistent and representative mean regional and seasonal aerosol load and distribution compared with the version 2 products (Koffi et al, 2012)
All of the seasonal average data points of the Taklamakan Desert and Tibetan Plateau are scattered in the upper right area, whereas those of the Northeast China Plain and Pearl River Delta are scattered in the lower left area
Summary
Atmospheric aerosols affect the radiative budget of the Earth–atmosphere system by direct interaction with solar radiation through scattering and absorption (Boucher et al, 2013). There exist few studies focusing on validating the CALIOP-observed aerosol vertical distributions over China, especially on the climatology of the seasonal average vertical profiles of the aerosol extinction coefficient. The seasonal aerosol vertical distribution over China has been studied using ground-based lidar observations at several sites (He et al, 2008; Huang et al, 2008a; Wu et al, 2011; Cao et al, 2013). The diverse natural and anthropogenic aerosol sources as well as the geographical and meteorological conditions and transport pathways make China a unique natural laboratory for examination of seasonal dust particles, biomass burning, anthropogenic pollution and aerosols of mixed types (Zhang et al, 2011; Zhang et al, 2015). Our study focuses on the seasonal aerosol vertical extinction profiles on a regional scale and the seasonal optical properties of dust particles, anthropogenic aerosols and aerosols of mixed types. The seasonal aerosol optical properties and vertical distributions are analyzed and discussed in Sects. 4 and 5, respectively
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