[Atmospheric Nitrogen Dioxide, Nitric Acid, Nitrate Nitrogen Concentrations, and Wet and Dry Deposition Rates in a...

Nitrogen dioxide (NO₂) and nitric acid (HNO₃) are nitrogen-containing acidic gases in the atmosphere, and they are important precursors of nitrate in aerosol and rainwater. The emission intensity of atmospheric nitrogen oxides is high in the subtropical region of China, but the concentrations and deposition rates of atmospheric nitrogen dioxide, nitric acid, particulate nitrate-nitrogen (NO₃^--N_p), and rainwater nitrate-nitrogen (NO₃^--N_r) in a double rice region in subtropical China are still unclear,. In this study, the atmosphere concentrations of NO₂-N, HNO₃-N, NO₃^--N_p in PM₁₀, and NO₃^--N_r and related meteorological parameters were simultaneously monitored in a typical double rice region within a subtropical hilly region of China, with the aim of determining the characteristics and influencing factors of NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r concentrations and quantifying the wet and dry deposition rates. The results showed that the annual mean concentrations of NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r were 4.2 μg·m^-3, 0.7 μg·m^-3, 4.0 μg·m^-3, and 1.0 mg·L^-1, respectively, and the deposition rates were 1.5, 3.2, 2.3, and 6.1 kg·hm^-2, respectively. The NO₂-N concentrations were negatively correlated with air temperatures, and the HNO₃-N concentrations were negatively correlated with wind speeds. TheNO₃^--N_p concentrations were negatively correlated with air temperatures, positively correlated with NO₂-N concentrations, but not significantly correlated with HNO₃-N concentrations, thus indicating that NO₂-N concentrations were an important limiting factor forNO₃^--N_p pollution in this study area. The NO₃^--N_r concentrations were negatively correlated with rainfall, as well as the concentrations of HNO₃-N and NO₃^--N_p. The annual total dry and wet depositions of the atmospheric NO₂-N, HNO₃-N, NO₃^--N_p, and NO₃^--N_r were 13.0 kg·hm^-2, which indicates that these compounds are important sources of nitrogen in paddy fields and may have significant impacts on paddy fields and surrounding ecosystems.