Quantifying the importance of vehicle ammonia emissions in an urban area of northeastern USA utilizing nitrogen isotopes

Abstract. Atmospheric ammonia (NH3) is a critical component of our atmosphere that contributes to air quality degradation and reactive nitrogen deposition; however, knowledge NH3 in urban environments remains limited. Year-long ambient related species were measured for concentrations the isotopic compositions (?15N) particulate ammonium (pNH4+) understand temporal sources chemistry northeastern US environment. We found pNH4+ elevated compared regional rural background monitoring stations, with seasonally significant variations. Local transported NHx (NH3+ pNH4+) identified using polar bivariate statistical back trajectory analysis, which suggested importance vehicles, volatilization, industry, stationary fuel combustion emissions. Utilizing uniquely positive ?15N(NH3) emission source signature from Bayesian stable isotope mixing model (SIMMR) indicates vehicles contribute 46.8±3.5 % (mean ±1?) annual level NHx, strong seasonal pattern higher relative contribution during winter (56.4±7.6 %) summer (34.1±5.5 %). The decrease vehicle emissions was be driven by temperature-dependent volatilization sources, fuel-combustion energy generation, change transport patterns based on wind direction, trajectory, inventory analysis. This work highlights reducing should considered improve wintertime this region.