Overlooked Nonagricultural and Wintertime Agricultural NH3 Emissions in Quzhou County, North China Plain: Evidence from 15N-Stable Isotopes

Ammonia (NH3) plays a critical role in atmospheric chemistry and can exacerbate haze formation. Agricultural emissions have been known as a primary source of global atmospheric NH3. However, with accelerating urbanization and optimized agricultural production, the dominance of agricultural emissions has become less clear. We investigated the contributions of nonagricultural and agricultural sources to atmospheric NH3 based on measurements of NH3 isotopes at nine sites in Quzhou County, a typical agricultural county in the North China Plain. We found that Quzhou had extremely high NH3 concentrations (annual average across all sites of 40.3 ± 3.3 μg m–3). We compared the sources of seasonal NH3 contributions in rural and urban areas through 15N-stable isotope analyses, which provides new insights into NH3 sources compared with the traditional emission inventories. In rural areas, agricultural sources (fertilizer application and livestock production) make significant contributions (56 ± 3%) to NH3 emissions in the winter, whereas there were larger contributions of nonagricultural sources [fossil fuel, waste, and biomass burning (56 ± 2%)] relative to agricultural sources in urban areas. More effective strategies are still needed for better manure management and vegetable/fruit production in the winter and for controlling nonagricultural sources, even in counties dominated by agriculture.