Long-term air pollution trend analysis in Malaysia

Air pollution has become increasingly significant in the last few decades as a major potential risk to public health in Malaysia due to rapid economic development, coupled with seasonal trans-boundary pollution. Over the years, air pollution in Malaysia has been characterised by large seasonal variations, which are significantly attributed to trans-boundary pollution. The aim of this study is to analyse the long-term temporal dynamic (1997–2015) of CO, NO x and PM 10 at 20 monitoring stations across Malaysia. Long-term pollutant trends were analysed using the Mann–Kendall test. For potential pollutant source analysis, satellite data and Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) backward trajectories model were employed. In all monitoring sites, we observed that the annual average concentrations of PM 10 were varied, with large coefficient variations. Meanwhile, CO and NOx were found to be less varied, with smaller coefficient variations, except in certain monitoring sites. Long-term analysis trends for CO attested to insignificant decreasing trends in 11 monitoring stations and increasing trends in seven stations. Meanwhile, NO x showed no significant trends in most stations. For PM 10 , five monitoring stations showed increasing trends, whereas 15 other stations showed decreasing trends. HYSPLIT backward trajectory analyses have shown that high seasonal PM 10 levels in most parts of Malaysia are due to trans-boundary pollution. Large-scale intense biomass burning in Indonesia, particularly during the southwest monsoon, has been identified as the main potential source. Long-term air pollution in Malaysia is characterised largely by trans-boundary pollution and is highly seasonal. In urban areas of Malaysian Peninsula, combinations of trans-boundary pollution and local emission sources were notably identified as important sources. Long-term PM 10 pollution in Malaysia shows small but significant decreasing trends. Therefore, to ensure that the effect of air pollution on human health is minimised, special attention needs to be focused on short-term pollution episodes, particularly during trans-boundary pollution events and extreme weather conditions such as El Niño.