Abstract
Ammonia (NH3) is the most abundant alkaline gas in the ambient air, and it is also one of the important precursors for the ammonium salts in aerosol and rainwater. Though the emission intensities of NH3 and acidic gases are high, the concentrations and deposition rates of atmospheric ammonia-nitrogen (NH3-N), particulate ammonium-nitrogen (NH4+-Np) and rainwater ammonium-nitrogen (NH4+-Nr) in double rice regions in subtropical China are still less known. In this study, atmospheric concentrations of NH3-N, NH4+-Np in PM10 and NH4+-Nr and related meteorological parameters were observed simultaneously in a typical double rice region in the subtropical hilly region of China, with the aim to clarify the characteristics and influencing factors of atmospheric NH3/NH4+-N concentrations and to quantify the wet and dry deposition rates of atmospheric NH3/NH4+-N. The results showed that the annual mean concentrations of nitrogen in NH3-N, NH4+-Np and NH4+-Nr were 5.7 μg·m-3, 12.8 μg·m-3 and 0.8 mg·L-1, respectively, and their deposition rates were 8.38, 5.61 and 9.07 kg·(hm2·a)-1, respectively. The NH3-N concentration was significantly increased after application of nitrogen fertilizer in the paddy field, and had a significant positive correlation with the air temperature. The NH4+-Np concentration did not show significant correlation with NH3-N concentration, indicating that atmospheric NH3-N concentration was not the main limiting factor for the NH4+-Np pollution in the studied region. The NH4+-Nr concentration was positively correlated with the NH4+-Np concentration but negatively correlated with precipitation. The high concentrations and deposition rates of atmospheric NH3-N/NH4+-N in the studied region indicated that the atmospheric NH3/NH4+-N pollution was serious, and atmospheric deposition of NH3/NH4+-N was an important nitrogen source in paddy fields, which should be considered in cropland nitrogen nutrient management.
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