Why do extreme particulate pollution events occur in low-emission Yunnan Province, China?

Yunnan Province in southwest China has low anthropogenic emissions, but in recent years it encountered unprecedented serious particulate pollution. To clarify the causes of pollution in this province, this study comprehensively analyzed the spatial-temporal distribution of near-surface PM2.5 (particles with aerodynamic diameter less than 2.5 μm) from 2017 to 2021, which was retrieved from Himawari-8 aerosol optical depth. The results show that, particulate pollution mainly occurred in the dry season (November to April), especially in March and April. And the heavily polluted areas mainly distributed in the southwest of the province, where there is small population and high forest cover. Dust, polluted dust, and elevated smoke were the most spatio-temporally variable aerosols, which should be attributed to biomass combustion and polluted air mass transportation from neighboring countries. The comparisons between effects of anthropogenic emissions, stable weather and pollutant transportation on local air quality indicate that exogenous pollutants should be mainly responsible for the concentrated outbreak of particulate pollution in Yunnan Province during the second half of the dry season. Besides, the stable weather conditions would further aggravate the deterioration of air quality. This study provides important reference for further strengthening joint prevention and control of regional air pollution.