Source, transport and impact of biomass burning emissions in spring 2024 in Yunnan, China

Unlike other regions in China, PM_2.5 concentrations in Yunnan's border cities exhibit a distinct seasonal pattern, with significantly higher levels in spring compared to other seasons. To obtain direct evidence of the impact of cross-border transport of biomass burning emissions on air quality in Yunnan, observations based on continuous lidar network measurements and manual PM_2.5 sampling were carried out in spring 2024 in Yunnan. The source and transport pathways of PM_2.5 in Yunnan were analyzed by combining ground-based observation data, satellite remote sensing fire-point data, model simulations and backward trajectory analysis. The significant positive correlation between PM_2.5 and CO concentrations in spring 2024 in Yunnan Province indicates typical biomass burning characteristics. Apparent pollution transport and settling events were observed with lidars. The good agreement of the spatial distribution of PM_2.5 and K⁺ concentrations also provide visual evidence of the impact of biomass burning emissions on the border cities of Yunnan. Cluster analysis and data assimilation results show that high concentration air mass from biomass burning of the South and Southeast Asia is an important cause of the surge in PM_2.5 in border cities. Notably, eastern Myanmar represents the dominant potential source of PM_2.5 for Yunnan's border cities in spring, with emissions from Myanmar's biomass burning contributing over 20 μg/m³ to local PM_2.5 levels.