Assessing Contributions of Agricultural and Nonagricultural Emissions to Atmospheric Ammonia in a Chinese Megacity

Ammonia (NH 3 ) is the predominant alkaline gas in the atmosphere contributing to formation of fine particles -a leading environmental cause of increased morbidity and mortality worldwide.Prior findings suggest that NH 3 in the urban atmosphere derives from a complex mixture of agricultural (mainly livestock production and fertilizer application) and non-agricultural (e.g., urban waste, fossil fuel-related emissions) sources; however, a citywide holistic assessment is hitherto lacking.Here we show that NH 3 from non-agricultural sources rivals agricultural NH 3 source contributions in the Shanghai urban atmosphere.We base our conclusion on four independent approaches: (i) a full-year operation of a passive NH 3 monitoring network at 14 locations covering urban, suburban, and rural landscapes; (ii) modelmeasurement comparison of hourly NH 3 concentrations at a pair of urban and rural supersites; (iii) source-specific NH 3 measurements from emission sources; and (iv) localized isotopic signatures of NH 3 sources integrated in a Bayesian isotope mixing model to make isotope-based source apportionment estimates of ambient NH 3 .Results indicate that non-agricultural sources and agricultural sources are both important contributors to NH 3 in the urban atmosphere.These findings highlight opportunities to limit NH 3 emissions from non-agricultural sources to help curb PM 2.5 pollution in urban China.