Impacts of Anthropogenic Emissions and Open Biomass Burning in South Asia and Southeast Asia on Air Quality and Meteorology Over Southern China

The emissions from South Asia and Southeast Asia significantly impact air quality and meteorological conditions in China. However, the individual or joint contributions of anthropogenic emissions and/or biomass burning from outside China to surface particulate matter with aerodynamic diameters less than 2.5 μm (PM_2.5) and aerosol optical depth (AOD) over southern China have not been fully investigated. Here, five experiments were designed to investigate the impacts of these emissions in January (winter), March (pre-monsoon), and October (post-monsoon) for 2017. Aerosols from South Asia and Southeast Asia contributed less to southern China during winter and post-monsoon seasons, whereas the wind patterns and emission intensity during the pre-monsoon season were conducive to the transport of aerosols. During pre-monsoon season, the total emissions contributed approximately 5.0 μg m⁻³ to surface PM_2.5 in Xizang Province. Biomass burning in Southeast Asia increased PM_2.5 in Yunnan Province by 37.9 μg m⁻³, while anthropogenic emissions increased it by 8.9 μg m⁻³. Transboundary aerosols can be transported to Xizang Province and Yunnan Province, primarily influencing PM_2.5 below 2 km height. It mainly affected PM_2.5 levels above the planetary boundary layer over southeast China. Aerosols from outside China can account for 79.5% and 54.8% AOD in Yunnan Province and southeast China, respectively. These aerosols reduced surface incident solar radiation by approximately 6%, leading to decreases in air temperature, wind speed, and boundary layer height. The findings are only applicable to the pre-monsoon season.