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

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 PM_2.5 concentrations were lower than polluted megacities such as Delhi but substantially higher than 24-h mean air quality guideline of the WHO. Levels of PM_2.5 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. SO₄^2-, NO₃^-, and major ions and NO₃^-/SO₄^2- 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.