title: Scavenging of PM2.5 by precipitation and the effects of precipitation pattern changes on health risks related to PM2.5 in Tokyo, Japan.
abstract: Fine particulate matter (aerodynamic diameter<2.5 μm; PM2.5) poses risks to human health. While precipitation is the main process for decreasing ambient pollutant concentrations, scavenging of PM2.5 by precipitation remains to be investigated. Here we formulated the processes of PM2.5 scavenging by precipitation from observed PM2.5 concentrations ([PM2.5]) and precipitation intensities. Then we analyzed how changes in precipitation patterns would affect health risks related to PM2.5 on the basis of a Monte Carlo simulation. Tokyo, the capital of Japan, was selected as the target for this study because of its social significance. We found that [PM2.5] decreased significantly through scavenging of PM2.5 from the atmosphere by precipitation. In contrast, we found no significant correlation between reduction of [PM2.5] and precipitation intensity. Our model for estimating the reduction of PM2.5 and the Monte Carlo simulation showed good agreement with observations. Among various changes in potential precipitation patterns, changes in the arithmetic mean of the number of events and/or in precipitation duration were more influential on reduction of [PM2.5] than changes in their standard deviations. Health risks due to PM2.5 will increase with decreases in precipitation duration and occurrence.
authors.affiliation: Department of Civil Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan; Institute of Engineering Innovation, School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ikeuchi
authors.affiliation: Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Komaba, Tokyo 153-8505, Japan and Department of Health Risk Communication, School of Medicine, Fukushima Medical University, 1 Hikariga-oka, Fukushima City, 960-1295, Japan E-mail: michio@fmu.ac.jp.
authors.forename: Michio
authors.initials: M
authors.lastname: Murakami
authors.affiliation: Institute of Engineering Innovation, School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Watanabe
mesh_terms: D000393:Air Pollutants; D002980:Climate; D003198:Computer Simulation; D004781:Environmental Exposure; D015386:Hazardous Substances; D006801:Humans; D007564:Japan; D008962:Models, Theoretical; D052638:Particulate Matter; D011891:Rain; D018570:Risk Assessment; D014041:Tokyo
chemical_list: D000393:Air Pollutants; D015386:Hazardous Substances; D052638:Particulate Matter