Simulation of the responses of rainstorm in the Yangtze River Middle Reaches to changes in anthropogenic aerosol emissions

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The model WRF-Chem sensitivity simulation experiments with changing intensity of anthropogenic emissions sources were applied to simulate a rainstorm process in the Yangtze River Middle Reaches (YRMR) during June 18–19, 2018 to study the responses of clouds and precipitation in the rainstorm to changes in aerosol concentrations in this region. The simulation experiments revealed that the aerosol-cloud interaction during low and high emission phases tended to inhibit and to enhance the precipitation process with the precipitation peak lagging 1–2 h. In the later period of rainstorm, high concentrations of aerosols improved precipitation efficiency significantly, resulting in more centralized clusters of intense precipitation. The cloud droplet number concentrations and cloud water contents demonstrated an increasing logarithmic relationship with increasing PM2.5 concentrations. The PM2.5 concentration of about 25 μg/m3 was estimated as the response threshold of cloud droplet number concentrations from sharp to smooth changes. Before and after the peak precipitation, the relationship between the average precipitation rates and PM2.5 concentrations presented an inverse power function. Aerosol-induced precipitation changes were sensitive to ambient relative humidity (RH). When 80% ≤ RH < 85%, the response of precipitation to aerosol emissions was in equilibrium. When RH < 80% or RH > 85% increasing anthropogenic aerosol emissions tended to inhibit or enhance precipitation, especially in the case of low (high) aerosol emissions.