Abstract
Abstract. Using 14 years (2007–2020) of data from passive (MODIS/Aqua) and active (CALIOP/CALIPSO) satellite measurements over China, we investigate (1) the temporal and spatial variation of aerosol properties over the Beijing–Tianjin–Hebei (BTH) region, the Yangtze River Delta (YRD), and the Pearl River Delta (PRD) and (2) the vertical distribution of aerosol types and extinction coefficients for different aerosol optical depth (AOD) and meteorological conditions. The results show the different spatial patterns and seasonal variations of the AOD over the three regions. Annual time series reveal the occurrence of AOD maxima in 2011 over the YRD and in 2012 over the BTH and PRD; thereafter the AOD decreases steadily. Using the CALIOP vertical feature mask, the relative frequency of occurrence (rFO) of each aerosol type in the atmospheric column is analyzed: rFOs of dust and polluted dust decrease from north to south; rFOs of clean ocean, polluted continental, clean continental and elevated smoke aerosol increase from north to south. In the vertical, the peak frequency of occurrence (FO) for each aerosol type depends on region and season and varies with AOD and meteorological conditions. In general, three distinct altitude ranges are observed with the peak FO at the surface (clean continental and clean marine aerosol), at ∼1 km (polluted dust and polluted continental aerosol) and at ∼3 km (elevated smoke aerosol), whereas dust aerosol may occur over the whole altitude range considered in this study (from the surface up to 8 km). The designation of the aerosol type in different height ranges may to some extent reflect the CALIOP aerosol type classification approach. Air mass trajectories indicate the different source regions for the three study areas and for the three different altitude ranges over each area. In this study nighttime CALIOP profiles are used. The comparison with daytime profiles shows substantial differences in the FO profiles with altitude, which suggest effects of boundary layer dynamics and aerosol transport on the vertical distribution of aerosol types, although differences due to day–night CALIOP performance cannot be ruled out.
Highlights
An aerosol is technically defined as a suspension of fine solid or liquid particles in a gas
Over each of the three regions, the annually averaged aerosol optical depth (AOD) varies in a similar way, with the AOD over the Pearl River Delta (PRD) about 0.1 lower than over the BTH and the Yangtze River Delta (YRD)
The annual mean AOD averaged over the whole study period is smallest in the PRD with a value of 0.41±0.09; over the BTH and the YRD the annual mean AODs averaged over the study period have similar values of 0.56 ± 0.07 and 0.55 ± 0.09, respectively
Summary
An aerosol is technically defined as a suspension of fine solid or liquid particles in a gas. Aerosol particles are characterized by their diameter, chemical composition and shape (both are size-dependent), and the number of aerosol particles of each size is described by the particle size distribution Each of these aerosol properties varies with time and space (Unger et al, 2008; Shindell et al, 2009). The chemical composition of the aerosol particles together with the amount of aerosol water determines the optical properties through the complex refractive index, which is important for the scattering and absorption of solar radiation in the atmosphere. The effects of these processes on climate (see below) are determined by the amount and size of the aerosol particles and the particle size distribution. In the presence of high concentrations of aerosol particles, more solar radiation is scattered and absorbed than in the presence of low concentrations, resulting in larger extinction and less radiation reaching the surface (Quan et al, 2014; Li et al, 2017; 2018)
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