Abstract
Nitrate (NO(3)(-)) is a crucial component of atmospheric pollutants, and understanding its sources and formation mechanisms holds significant importance for air pollution control. In this study, stable isotope techniques and Bayesian Mixing Models (Mix SIAR) were applied to analyze the primary sources and formation processes of NO(3)(-) in PM(2.5) and PM(10) in Beijing in 2022. The results indicate that the contribution of vehicle exhaust, coal combustion, biomass burning, and soil emissions to NO(3)(-) in PM(2.5) were 33.9%, 20.5%, 29.8%, and 15.9%, respectively, while for PM(10), the contributions were 30.6%, 21.6%, 29.9%, and 17.9% respectively. An analysis of δ(18)O-NO(3)(-) values indicated that the contribution of N(2)O(5) hydrolysis to NO(3)(-) in PM(2.5) and PM(10) over the year was 64.0% and 75.6%, respectively, highlighting its predominant role in nitrate formation. Nevertheless, the gas-phase reaction of NO(2) with ·OH radicals was notably more pronounced in summer. Compared to PM(10), the gas-phase reaction of NO(2) with ·OH radicals contributes more to NO(3)(-) in PM(2.5). These results offer a vital foundation for further research into the sources and formation mechanisms of atmospheric NO(3)(-) and provide scientific support for measures to prevent and control air pollution.