4:30 PM - 4:45 PM
[AAS11-28] Quantification of PM2.5 concentration reduction during rainfall due to below-cloud scavenging based on observations and simulations.
Keywords:aerosol, wet scavenging, meteorology-chemistry model
For accurate climate prediction, aerosol concentrations in the atmosphere must be correctly quantified. The wet scavenging process is considered important for determining atmospheric aerosol concentrations (Chate, 2005; Bae et al., 2012). Although aerosol reduction during rainfall and snowfall has been quantified by analysis of observational data (Fujino and Miyamoto, 2022; Fujino et al., 2025), the details of the wet scavenging process have not been discussed. Therefore, the purpose of this study is to quantify the reduction and scavenging rate of PM2.5 concentration during rainfall events in Japan using observational data and meteorology-chemistry simulations, and to determine the impact of below-cloud scavenging on changes in PM2.5 concentration during rainfall events.
In this study, we used Offline SCALE-Chem (Nakata et al., 2021), an offline coupled meteorology model (Nishizawa et al., 2015; Sato et al., 2015) and chemical transport model (Kajino et al., 2019; Kajino et al., 2021). The initial and boundary conditions were obtained from MANL and the calculation period was from 00UTC on Oct. 1st to 00UTC on Oct. 30th, 2019. Analysis of the contribution of the below-cloud scavenging process to the change in the average of PM2.5 concentrations showed that the average reduction was 17.92% at the ground surface and 9.45% in the vertical direction. The average contribution of below-cloud scavenging to the total wet deposition process was 41.23% for sulfate and 49.87% for nitrate. The composite analysis showed a dramatic decrease in PM2.5 concentration from 1 h before to 1 h after the onset of rainfall, 9.76% for observation and 10.88% for simulation. We calculated aerosol scavenging rate (Feng and Wang, 2012; Olszowski, 2016; Fujino and Miyamoto, 2022; Fujino et al., 2025) for each rainfall events. The average scavenging rate was 15.34% for observation and 19.35% for simulation. We quantified the amount of change and contribution rates of PM2.5 concentration due to below-cloud scavenging and the amount of decrease and scavenging rates of PM2.5 concentration due to rainfall.
In this study, we used Offline SCALE-Chem (Nakata et al., 2021), an offline coupled meteorology model (Nishizawa et al., 2015; Sato et al., 2015) and chemical transport model (Kajino et al., 2019; Kajino et al., 2021). The initial and boundary conditions were obtained from MANL and the calculation period was from 00UTC on Oct. 1st to 00UTC on Oct. 30th, 2019. Analysis of the contribution of the below-cloud scavenging process to the change in the average of PM2.5 concentrations showed that the average reduction was 17.92% at the ground surface and 9.45% in the vertical direction. The average contribution of below-cloud scavenging to the total wet deposition process was 41.23% for sulfate and 49.87% for nitrate. The composite analysis showed a dramatic decrease in PM2.5 concentration from 1 h before to 1 h after the onset of rainfall, 9.76% for observation and 10.88% for simulation. We calculated aerosol scavenging rate (Feng and Wang, 2012; Olszowski, 2016; Fujino and Miyamoto, 2022; Fujino et al., 2025) for each rainfall events. The average scavenging rate was 15.34% for observation and 19.35% for simulation. We quantified the amount of change and contribution rates of PM2.5 concentration due to below-cloud scavenging and the amount of decrease and scavenging rates of PM2.5 concentration due to rainfall.