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 (PM2.5) pollution is one of the major issues affected by climate change, especially in tropical areas such as Southeast Asia. However, the PM2.5 formation mechanism and the climate-driven impacts on PM2.5 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 PM2.5 over Southeast Asia, identifying the PM2.5 regime in Southeast Asia and analyzing the role of ammonia (NH3) in the PM2.5 formation. We then projected PM2.5 under various Shared Socioeconomic Pathways (SSPs) scenarios, evaluating the impacts of climate change on PM2.5 and the resultant human health impacts and economic costs. We found that NH3 reductions had minimal impact on PM2.5 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 PM2.5 in Southeast Asia. Under climate change, the overall PM2.5 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 PM2.5-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 PM2.5-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 PM2.5 control policy is essential to mitigate PM2.5 pollution, as well as the resultant human health impacts and economic costs in Southeast Asia under climate change.