Aggravated multi-source air pollution exposure caused by open fires in China

Open fires produce pollutants that critically harm human health. Differences in emission characteristics and toxic substances from the burning of different biomasses lead to distinct exposure patterns. However, the details of these exposure patterns are still poorly known due to the uncertainties regarding cross-region transport. In this study, we investigated the particulate matters (PM) and ozone (O3) pollution produced by open fires from different vegetation types and locations, and assessed their exposure risks throughout China, by using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model combined with multi-source spatial data. Results revealed that open fires significantly enhanced the pollutant concentrations in China, which aggravated the risks of PM2.5 and O3 exposures for 303 million and 405 million people, respectively. Compared with cropland fires, forest and grassland fires had greater impacts on PM2.5 exposure, significantly increasing exposure risk for 208 million people in southern China. Cropland fires contribute more to O3 exposure in central and eastern China, which could increase the risk for 341 million people. For the location factor, the fires outside China, mainly forest and grassland burning, affected more than 74 million people, while domestic fires, mainly cropland burning, affected 354 million people. Therefore, the results suggest that the burning vegetation type and cross-region transport of pollutants should be considered in the formulation of national and regional pollution control measures, especially in densely populated areas.