Simulating the impact of biomass burning aerosols on an intensive precipitation event in urban areas of the Pearl River Delta

Abstract

The impact of biomass burning aerosols (BBAs) on heavy precipitation during an urban precipitation event on 21 February 2019 was simulated using WRF-Chem v 4.1.2 model. Two tests were conducted: one that considered BBAs and the other that did not. The results showed that, when BBAs were considered, the simulation performance was improved, with the positioning of the high-value precipitation area being more precise. The main precipitation area was dominated by convective precipitation surrounded by mixed precipitation. The stratiform precipitation accounted for the largest proportion (>40%). The intensity, spatial scope, and the persistence of the precipitation were suppressed due to BBAs. This suppression can be attributed to the enhancement in atmosphere stability induced by the BBAs, which weakened the vertical motion and the moisture transport. The convective (mixed) precipitation rate was enhanced by 0.5 mm/h (0.2 mm/h). The stratiform precipitation rate was weakened by 1.5 mm/h, which contributes the major suppression effect due to BBAs on precipitation. BBAs inhibited the condensation of cloud droplets and further inhibited the cloud formation under zero isotherm line. The weakened upward transport of moisture facilitated the formation of ice hydrometeors at lower levels. The major cloud microphysical processes related with the BBA-induced change were the condensation of cloud droplets, the collision and coalescence of cloud droplets by rain, and the melting of hail into rain.