Numerical assessment of PM2.5 and O3 air quality in Continental Southeast Asia: Impacts of potential future climate change

Changing climate will impact future air quality. In this study, an online coupled meteorology and chemistry WRF-CMAQ model was applied to simulate such impacts on future O3 and PM2.5 air quality over Continental Southeast Asia. Simulations were conducted for present (2006–2015) and future (2046–2055) years under two climate scenarios, RCP4.5 and RCP8.5. Future climate projections were obtained by implementing a downscaling dynamical method based on pseudo global warming technique. In order to estimate the impacts of climate change alone, anthropogenic and biomass burning emissions were held constant at present level while biogenic emissions varying with climate were used. The model results indicated a future regional meteorology characterized by a warmer and more humid atmosphere, increased precipitation, and more stagnant condition. Affected by climate change, NOx and NMVOCs biogenic emissions increase which contribute to the increasing effects on O3 and PM2.5 precursors concentrations. Subsequently, the changes in meteorology and biogenic emission affect air quality. These influence on ground level O3 and PM2.5 are different between the two climate scenarios. Under RCP4.5 scenario, future atmosphere appears to be reduced in O3 and PM2.5 concentrations, suggesting a potential “climate benefit” for air quality. At four target countries, namely Cambodia, Laos, Thailand, and Vietnam, O3 concentration decreases by −0.76 ppb (−2.40%), PM2.5 concentration decreases by −0.95 μg/m3 (−4.32%) on average for the entire year. However, climate change worsen O3 and PM2.5 air pollution under RCP8.5 scenario. O3 concentration increases by +0.26 ppb (+0.84%), PM2.5 concentration increases by +0.92 μg/m3 (+4.20%) on average for the entire year. Significant increases were generally located in northern Vietnam (for O3) and southern Vietnam (for PM2.5) during the dry season. The analysis suggests that the decrease in O3 concentration is due to the dominancy of the negative effect of water vapor increase and the increase in O3 concentration is affected largely by the temperature increase, stagnant condition, and biogenic emission increase. The responses of PM2.5 to climate change depend on the physical and chemical characteristics of each PM2.5 species. The major climate change effect on PM2.5 is the physical effect, rather than the chemical effect.