PM_2.5 decrease with precipitation as revealed by single‐point ground‐based observation

Abstract

This study analyzed the observed data of precipitation and PM2.5 concentration collected over two and a half years at Tsujido, Fujisawa City, to examine a quantitative relationship between the two quantities. It was observed that the PM2.5 concentration decreased as precipitation increased. A composite analysis revealed that the PM2.5 concentration on average decreases by 20.99% 1 h after the onset of precipitation as compared to that 1 h before, which is statistically significant based on a paired t‐test. The PM2.5 concentrations decreased over 8 h period from 5 h (−5 h) before to 3 h (+3 h) after the onset of precipitation, with a particularly dramatic decrease at the onset of precipitation. Analysis of PM2.5 scavenging rates by precipitation intensity showed that the scavenging rate was 2.03% for light precipitation events, 28.15% for moderate precipitation events, and 26.75% for heavy precipitation events, indicating that the scavenging rate increased with moderate precipitation intensity and above. It is suggested that the deposition processes of rainout and washout are effective in reducing PM2.5 concentration with precipitation.

New Insights Into Scavenging Effect of Aerosol Species During Summer Rainfall Process in Beijing

“…One explanation is the enhanced gas‐particle partitioning driven by high humidity and low temperature exceeded the weak scavenging effect of rainfall. Overall, our results show that over 30% decreases in aerosol species are due to the changes in wind speed before rain starts, while the further decreases associated with wet scavenging occur mainly within 1 hour or even less, similar to the results reported in Fujisawa City (Fujino & Miyamoto, 2022; Ouyang et al., 2015).…”

“…The change percentages of aerosol species before and after rainfall processes with different intensities were also different (Yue Sun et al., 2019). All PM 2.5 chemical species except nitrate, chloride and POA showed continuously enhanced decreases in mass concentrations with increasing rainfall intensity (Fujino & Miyamoto, 2022), especially LO‐OOA showing a change percentage of more than 50% after the heavy rainfall process due to the reduced photochemical production. In contrast, the increases in nitrate, chloride and ammonium after moderate rainfall process sometimes even exceeded those during weak rainfall, likely due to the facilitated gas‐particle partitioning under lower temperature and higher RH conditions (Figure S10 in Supporting Information ).…”

Low-cost PM2.5 sensors can help identify driving factors of poor air quality and benefit communities

“…Precipitation (inches, measured hourly at the Waterbury-Oxford Airport) generally has a negative relationship at each site, also conceptually sensible as precipitation tends to mitigate PM [ 33 ]. Data were not amenable to decile means analysis given the relatively low amounts of rainfall and snowfall during the study period at any given time.…”