Effects of climate change on PM2.5 formation chemistry, and the associated human health impacts and economic costs in Southeast Asia

Climate change poses a significant threat to both the environment and human health. Fine particulate matter (PM_2.5) pollution is one of the major issues affected by climate change, especially in tropical areas such as Southeast Asia. However, the PM_2.5 formation mechanism and the climate-driven impacts on PM_2.5 levels, compositions, human health, and economy in Southeast Asia have yet to be thoroughly assessed. Here, we employed regional climate and air quality models to simulate PM_2.5 over Southeast Asia, identifying the PM_2.5 regime in Southeast Asia and analyzing the role of ammonia (NH₃) in the PM_2.5 formation. We then projected PM_2.5 under various Shared Socioeconomic Pathways (SSPs) scenarios, evaluating the impacts of climate change on PM_2.5 and the resultant human health impacts and economic costs. We found that NH₃ reductions had minimal impact on PM_2.5 concentration in Southeast Asia due to the prevalent NH₃-rich conditions in the region. Controlling volatile organic compounds (VOC) and sulfur dioxide (SO₂) is more effective in reducing secondary PM_2.5 in Southeast Asia. Under climate change, the overall PM_2.5 concentration in Southeast Asia was projected to decrease by ∼2-10 % by 2050 under all scenarios, notably for secondary organic aerosol (SOA) levels (∼41-61 %) driven by future warmer climate conditions. The total PM_2.5-attributed premature mortality in Southeast Asia was projected to increase by ∼7 % under SSP126 and ∼10 % under SSP585 by 2050, particularly in Indonesia and Thailand. The increased PM_2.5-attributable premature mortality is estimated to induce an economic loss of $447 and $591 billion (in 2019 USD), respectively, under SSP126 and SSP585 by 2050. Therefore, a more stringent PM_2.5 control policy is essential to mitigate PM_2.5 pollution, as well as the resultant human health impacts and economic costs in Southeast Asia under climate change.