Effects of Air Pollution on Rainfall Microphysics Over the Yangtze River Delta

Herein, the raindrop size distribution (DSD) and rainfall microphysics characteristics are investigated at multiple stations within the Yangtze River Delta (YRD) under two air pollution conditions. Raindrop data from 14 Thies Clima Laser Precipitation Monitor disdrometers spanning approximately 2 years were employed together with corresponding air pollution data. Rain gauge data and several types of meteorological data were also used. The DSD characteristics were found to vary across the YRD; thus, we compiled DSD-based demarcations between convective rain and stratiform rain at each site. During summer, the average mass-weighted mean drop diameter parameter value was higher by a mean 20%, and the average normalized intercept parameter value was lower by a mean 12% in polluted atmosphere conditions for both convective rain and stratiform rain, as well as for different rainfall intensity classes. The differences in atmospheric conditions between clear and polluted air conditions partially account for the uncertainties in the DSD characteristics. Air pollution resulted in uncertainty in the shape parameter-slope parameter relationship and in the rainfall kinetic energy-rainfall intensity (KE-R) relationship. The air pollution index can be integrated into the KE-R relationship to improve the KE simulation accuracy. In addition, air pollution causes some uncertainty in the radar reflectivity-rainfall intensity (Z-R) relationship, while the acceptable deviation of the Z-R relationship did not significantly impact the accuracy of rainfall simulations. This study improves our understanding of DSD and provides a comprehensive overview of the relationship between air pollution and rainfall microphysics for a typical urban agglomeration area.