Abstract
Chengdu is a typical basin city of Southwest China with rare observations of remote sensing measurements. To assess the climate change and establish a region aerosol model, a deeper understanding of the separated volume size distribution (VSD) and complex refractive index (CRI) is required. In this study, we employed the sub-mode VSD and CRI in Chengdu based on the three years observation data to investigate the sub-mode characteristics and climate effects. The annual average fraction of the fine-mode aerosol optical depth (AODf) is 92%, which has the same monthly tendency as the total AOD. But the coarse-mode aerosol optical depth (AODc) has little variation in different months. There are four distinguishing modes of VSD in Chengdu; the median radii are 0.17 μm ± 0.05, 0.31 μm ± 0.12, 1.62 μm ± 0.45, 3.25 μm ± 0.99, respectively. The multi-year average and seasonal variations of fine- and coarse-mode VSD and CRI are also analyzed to characterize aerosols over this region. The fine-mode single scattering albedos (SSAs) are higher than the coarse-mode ones, which suggests that the coarse-mode aerosols have a stronger absorbing effect on solar light than the small-size aerosol particles in Chengdu.
Highlights
As one component of the terrestrial atmosphere, aerosol is an important factor in global climate change, with direct effects and indirect effects
It is demonstrable that the fine-mode aerosols are the principal pollutant in Chengdu area, which lead to the change of aerosol optical depth (AOD)
There are two main reasons: firstly, the average surface wind speed all over the basin is low under the control of subtropical anticyclone in summer [38], which makes aerosol transport to other regions difficult
Summary
As one component of the terrestrial atmosphere, aerosol is an important factor in global climate change, with direct effects and indirect effects. Direct effects include changing the radiation balance of the Earth-atmosphere system by absorbing and scattering sunlight [1,2]. Aerosol serves as cloud condensation nuclei (CCN) involved in cloud microphysics processes, referred to as indirect effects [3]. Chengdu, located in the central region of the Sichuan basin (Chengdu Plain) with a population of ~16 million (the resident population of Chengdu was counted in 2016), is the economic center and transportation hub in southwest China. Due to the special topography of the basin, the average wind speed is low [5,6].
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