Assessment major NOx sources to nitrate of TSP around the Danjiangkou reservoir using isotopes and a Bayesian isotope mixing model

Nitrate (NO 3 - ) is a key component of atmospheric particulate matter. However, studies quantifying NO 3 - formation and sources in water source areas remain scarce. This study employs NO 3 - concentration, dual isotopic analyses ( delta 15 N, delta 18 O), and SIAR and PSCF models to elucidate NO 3 - formation mechanisms and apportion sources in the Danjiangkou Reservoir area. The result showed that the concentration of NO 3 - (0.52 mu g m -3 -2.39 mu g m -3 ), delta 15 N-NO 3 - (- 2.3 parts per thousand-4.2 parts per thousand) and delta 18 O-NO 3 - (64.2 parts per thousand - 96.6 parts per thousand) values varied seasonally in total suspended particulate matter (TSP). The contribution of the NO 2 + center dot OH pathway was the highest in summer (84%), while the main contributions came from the N 2 O 5 + H 2 O and NO 3 + VOCs pathways in winter (75%). The SIAR model revealed that the contributions of coal combustion and traffic emissions were 34% and 23%, respectively, indicating that fossil fuel release contributed most. Moreover, the contribution of biomass combustion sources was 31%, and soil emission sources had the least (12%). Considering liquefied petroleum gas, gasoline, and diesel vehicles as traffic emission sources, their contribution to NO 3 - in TSP increased to 50%. The PSCF analysis indicated that external input areas were predominantly from central Henan Province, northern Hubei Province, and central Shaanxi Province. This study quantitatively analyzed the sources of NO 3 - in atmospheric particulate matter in water sources for the first time, indicating that controlling the emissions of nitrogen oxides from gasoline cars, heavyduty diesel trucks, and ships could help alleviate haze pollution and enhance air quality in the Danjiangkou reservoir area.