Simulated influence of air pollution and aerosols on summer precipitation over the Pearl River Delta region

A simulation study of precipitation processes in summer over the Pearl River Delta region was conducted using the Weather Research and Forecasting Model coupled to with Chemistry, WRF-Chem. We investigated the influence of air pollution and aerosols on the summertime heavy precipitation over the subtropical regions. The study showed the following results. (1) The control test can simulate the largescale meteorological conditions and the mesoscale weather processes well. The chemistry module (CHEM) had only a small influence on the simulation of the macroscale environmental field. Simulations of mesoscale weather processes could be improved by including atmospheric chemistry modules and anthropogenic aerosols. (2) Even though air pollution and aerosols can reduce solar shortwave radiation received by the ground, they increase downward longwave radiation from the atmosphere. Heating atmosphere by aerosols may increase stability and suppress convection. However, aerosols suppress the conversion of cloud water into rainwater and cloud ice, restricting heavy precipitation by reducing the collision–coalescence process during strong precipitation. Aerosols extend the lifetime of clouds and increase cloud cover, contributing to maintaining the precipitation. (3) Indirect and direct aerosol effects have significantly different functions in precipitation. The direct effect primarily has a positive function on the formation of rainwater, while the indirect effect suppresses increases in the precipitation intensity and contributes to maintaining the precipitation. But the notable invigoration effect was not found.