资源环境科技发展态势分析平台

Abstract. Atmospheric ammonia (NH₃) is a critical component of our atmosphere that contributes to air quality degradation and reactive nitrogen deposition; however, our knowledge of NH₃ in urban environments remains limited. Year-long ambient NH₃ and related species were measured for concentrations and the nitrogen isotopic compositions (δ¹⁵N) of NH₃ and particulate ammonium (pNH₄⁺) to understand the temporal sources and chemistry of NH₃ in a northeastern US urban environment. We found that urban NH₃ and pNH₄⁺ concentrations were elevated compared to regional rural background monitoring stations, with seasonally significant variations. Local and transported sources of NH_x (NH₃ + pNH₄⁺) were identified using polar bivariate and statistical back trajectory analysis, which suggested the importance of vehicles, volatilization, industry, fuel combustion, and biomass burning emissions. Utilizing a uniquely positive δ¹⁵N(NH₃) emission source signature from vehicles, a Bayesian stable isotope mixing model indicates that vehicles contribute 30.7±11.6 % (mean±1σ) to the annual background level of urban NH_x, with a strong seasonal pattern with higher relative contribution during winter (45.8±13.0 %) compared to summer (20.8±9.7 %). The decrease in the relative importance of vehicle emissions during the summer was suggested to be driven by temperature-dependent NH₃ emissions from volatilization sources based on wind direction, back trajectory, and NH₃ emission inventory analysis. This work highlights that reducing vehicle NH₃ emissions should be considered to improve wintertime air quality in this region.