Airborne particulate matter in Southeast Asia: a review on variation, chemical compositions and source apportionment

Environmental context Airborne particulate matter (PM) is a major public health risk in Southeast Asia. The annual average concentration of fine PM (PM2.5) in the region is significantly higher than the WHO air quality guidelines, and higher PM2.5 levels were recorded during dry seasons, primarily due to biomass burning. In this paper, we provide an overview of the seasonal variations in concentrations, chemical compositions, and sources of PM in Southeast Asian countries. Abstract Airborne particulate matter (PM) in Southeast Asia is the most important air pollutant, causing millions of premature deaths. This review provides an overview of the levels, chemical compositions and sources of PM and compared these with studies from megacities in other regions. Daily average PM2.5 concentrations were lower than polluted megacities such as Delhi but substantially higher than 24-h mean air quality guideline of the WHO. Levels of PM2.5 in maritime continental Southeast Asia (Indonesia, Brunei, Malaysia, Philippines and Singapore) were lower than in mainland continental countries (Cambodia, Myanmar, Thailand, Vietnam, and Laos). PM levels are usually two times higher during dry than wet seasons. Organic carbon is a key chemical component, contributing 9–52% of PM mass. SO42−EN22044_IE1.gif, NO3−EN22044_IE2.gif, and NH4+EN22044_IE3.gif are major ions and NO3−EN22044_IE4.gif/SO42−EN22044_IE5.gif ratios were notably lower than in megacities in other regions, implying lower emissions from mobile relative to stationary sources. Source apportionment indicates biomass burning is one of the most important sources, particularly during the haze (dry) seasons, followed by road traffic emission in dense-traffic cities such as Bangkok, Kuala Lumpur and Hanoi. The secondary aerosols contribution to PM mass is usually lower than that in cities from other regions. We suggest future PM source apportionment studies in Southeast Asia to include both inorganic and organic tracers and apply both chemical mass balance and multivariate receptor models.