Changes in source composition of wet nitrate deposition after air pollution control in a typical area of Southeast...

In recent years, China has adopted numerous policies and regulations to control NO_x emissions to further alleviate the adverse impacts of NO₃^--N deposition. However, the variation in wet NO₃^--N deposition under such policies is not clear. In this study, the southeastern area, with highly developed industries and traditional agriculture, was selected to explore the variation in NO₃^--N deposition and its sources changes after such air pollution control through field observation and isotope tracing. Results showed that the annual mean concentrations of NO₃^--N in precipitation were 0.67 mg L^-1 and 0.54 mg L^-1 in 2014-2015 and 2021-2022, respectively. The average wet NO₃^--N depositions in 2014-2015 and 2021-2022 was 7.76 kg N ha^-1 yr^-1 and 5.03 kg N ha^-1 yr^-1, respectively, indicating a 35% decrease. The δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- values were lower in warm seasons and higher in cold seasons, and both showed a lower trend in 2021-2022 compared with 2014-2015. The Bayesian model results showed that the NO_x emitted from coal-powered plants contributed 53.6% to wet NO₃^--N deposition, followed by vehicle exhaust (22.9%), other sources (17.1%), and soil emissions (6.4%) during 2014-2015. However, the contribution of vehicle exhaust (33.3%) overpassed the coal combustion (32.3%) and followed by other sources (25.4%) and soil emissions (9.0%) in 2021-2022. Apart from the control of air pollution, meteorological factors such as temperature, precipitation, and solar radiation are closely related to the changes in atmospheric N transformation and deposition. The results suggest phased achievements in air pollution control and that more attention should be paid to the control of motor vehicle exhaust pollution in the future, at the same time maintaining current actions and supervision of coal-powered plants.