To study the scavenging effect of precipitation on fine particulate matter (PM2.5), a type of air pollutants that can lead to serious health problems, the principal components of PM2.5, namely, organic carbon, elemental carbon, and major inorganic ions, in the atmosphere and rainwater, were measured and analyzed from September 2015 to March 2017 at suburban and urban sites in the Bangkok Metropolitan Region in Thailand. This is the first study of this kind conducted in tropical areas.
The results of the analysis confirmed that the scavenging ratios (SR), indicators of removal by precipitation, for PM2.5 components were in the order of major inorganic ions (nitrate and sulfate ions) > organic carbon > elemental carbon (fossil fuel origin) > elemental carbon (biomass combustion origin). Conversely, the wet deposition amounts of the components ranked in the order of nitrate ions > water-soluble organic carbon > sulfate ions > water-insoluble organic carbon > elemental carbon, suggesting that there are more abundant components originated by secondary particles produced by atmospheric chemical reactions in precipitation than that of primary particles emitted directly from the source.
This article was produced on the basis of the outcome of the research project of the JICA Ogata Sadako Research Institute for Peace and Development, “A Study on Urban Air Pollution Improvement in Asia,” and published in an academic journal, Atmospheric Environment.