A Decadal Change in Atmospheric Nitrogen Deposition at a Rural Site in Southern China.

Elevated atmospheric reactive nitrogen (Nr) emissions and the subsequent nitrogen (N) deposition have negatively impacted the global environment, particularly in China. In order to assess the long-term trends in atmospheric N deposition in the south of China, Taojiang County in Hunan Province was selected as a representative rural area for study. We analyzed interannual variation in atmospheric Nr, including gaseous ammonia (NH₃), nitrogen dioxide (NO₂), nitrate acid (HNO₃) vapor, particulate ammonium (NH₄⁺), and nitrate (NO₃⁻) in air and NH₄⁺-N and NO₃⁻-N in precipitation from 2011 to 2020. The 10-year average atmospheric wet-plus-dry N deposition was 41.9 kg N ha⁻¹ yr⁻¹, which decreased by approximately 24% after 2012, indicating that NH₃ and NO_x emissions were effectively reduced by emission controls introduced in 2013. Wet deposition accounted for approximately 74% of the total N deposition and was significantly influenced by annual precipitation amount. Reduced N (NH₃, pNH₄⁺, and NH₄⁺ in rainwater) was the dominant form, comprising approximately 58% of the total N deposition, while oxidized N (pNO₃⁻, NO₂, HNO₃, and NO₃⁻ in rainwater) accounted for 42% of the total N deposition. Atmospheric HNO₃, NO₂, and NH₃ concentrations and deposition declined by 30–80% over the decade, while particulate NH₄⁺ and NO₃⁻ concentrations and deposition remained at relatively stable levels, which suggests that ongoing research and policy should focus on rural particulate pollution. Future strategies must concentrate on the integrated control of NH₃ and NO_x emissions to mitigate air pollution and protect human health, particularly in rural areas because current abatement efforts are primarily directed toward urban areas and the industrial sector, whereas non-point source NH₃ pollution, influenced mainly by agricultural activities, dominates in rural regions. [ABSTRACT FROM AUTHOR]