PM_2.5 Concentration Decreases with Snowfall as Revealed by Surface Observation Data

Abstract

The quantitative relationship between the observed snowfall and PM_2.5 concentration data collected at Niigata Prefecture, Japan, was examined. The PM_2.5 concentration decreased as snowfall increased. A composite analysis revealed that the PM_2.5 concentration decreased by 27.33% from 1 h before to 1 h after the onset of snowfall, which is statistically significant. The average PM_2.5 concentration for all snowfall events decreased over a total of three hours, from 2 h before to 1 h after the onset of snowfall. The average PM_2.5 scavenging rate for all snowfall events was 6.15 × 10⁻⁶ s⁻¹, which was much higher than that for rainfall events. The scavenging rates were positive at relative humidity (RH) between 50% and 75% and above 95%. It is suggested that the deposition processes of wet scavenging are effective, both in reducing PM_2.5 concentration during snowfall and in the RH dependence of scavenging rates.