Global impact of fire emission on ambient nitrate (NO₃^-) and health effects during 2005–2019

Smoke from fires often aggravate ambient nitrate pollution and pose significant threats to human health because nitrate showed high exposure-response coefficient. To better assess the impact of fire emissions on ambient nitrate and public health, a multi-stage model was developed to optimize fire-related ambient nitrate concentrations globally. Then, the mortalities caused by fire-sourced ambient nitrate exposure were estimated based on the health risk assessment model. The results suggest that the global annual mean fire-induced nitrate (NO₃^-) concentration during 2005–2019 was 0.19 ± 0.14 μg/m³. Spatially, fire-related NO₃^- showed the highest concentration in Sub-Saharan Africa (1.47 ± 0.78 μg/m³), followed by Australia (0.40 ± 0.22 μg/m³) and South America (0.30 ± 0.18 μg/m³), with the lowest level in Western Europe (0.11 ± 0.06 μg/m³), which was closely linked with burned areas and fuel consumption. Additionally, fire-related NO₃^- levels in India (89 %), Australia (66 %), and North America (57 %) experienced rapid increases from 2005 to 2019. Unlike exposure concentrations, fire-induced mortalities were higher in China (113,372 deaths) and India (82,880 deaths) because regions with frequent fires overlapped with high population density areas in these countries. These results demonstrate the necessity of refraining from such burns to improve global air quality and mitigate health damages. Furthermore, our study challenges the traditional view and confirms that both of China and India experience the most serious fire-related nitrate health risks.