Atmospheric reactive nitrogen concentration and deposition trends from 2011 to 2018 at an urban site in north China

Atmospheric reactive nitrogen (Nr) emissions and deposition have caused much damage to the global environment and also impacted human health. Determining long-term trends in atmospheric Nr concentrations and deposition is important for evaluating air quality and ecosystem effects and formulating control measures to reduce negative impacts. We measured monthly concentrations of NH3, pNH4þ, HNO3, pNO3 -, and NO2 and calculated their dry deposition rates using an inferential method from 2011 to 2018 at an urban site in Zhengzhou in the North China Plain. Inorganic N (NH4+ and NO3- ) concentrations in precipitation and wet/bulk N deposition were also quantified in 2011, 2016, 2017 and 2018. The results showed high concentrations of atmospheric Nr species, with considerable variation in some species over the monitoring period. Annual mean NH3 concentrations significantly increased from 2011 to 2018 (p < 0.001) with that in 2018 being twice that in 2011. However, pNO3- and pNH4þ concentrations decreased after 2013. The annual mean NO2 concentration in 2018 had decreased by 33.4% compared to the peak in 2011. Highest NH3 concentrations were measured in spring or summer, and lowest concentrations in winter. pNH4þ and pNO3- concentrations peaked mainly in winter. Total annual dry N deposition ranged from 21.9 to 41.2 kg N ha-1. Bulk NH4þ and NO3- deposition was lower in 2016–2018 than in 2011. However, atmospheric Nr concentrations and N deposition remained high in this urban ecosystem. NH3 emissions urgently need control measures, and Nr impacts on the surrounding ecosystems and human health should be considered. Continuous long-term measurements of atmospheric Nr concentrations and deposition at a regional scale are necessary to help formulate emission control measures and protect human and ecosystem health.