Atmospheric Nitrogen Dioxide, Nitric Acid, Nitrate Nitrogen Concentrations, and Wet and Dry Deposition Rates in a Double Rice Region in Subtropical China

Abstract

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--Np), and rainwater nitrate-nitrogen (NO3--Nr) in a double rice region in subtropical China are still unclear,. In this study, the atmosphere concentrations of NO2-N, HNO3-N, NO3--Np in PM10, and NO3--Nr 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--Np, and NO3--Nr concentrations and quantifying the wet and dry deposition rates. The results showed that the annual mean concentrations of NO2-N, HNO3-N, NO3--Np, and NO3--Nr 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--Np 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--Np pollution in this study area. The NO3--Nr concentrations were negatively correlated with rainfall, as well as the concentrations of HNO3-N and NO3--Np. The annual total dry and wet depositions of the atmospheric NO2-N, HNO3-N, NO3--Np, and NO3--Nr 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.