Source apportionment of atmospheric ammonia in suburban Beijing revealed through N-stable isotopes.

Addressing the urgent issue of atmospheric ammonia (NH) emissions is crucial in combating poor air quality in megacities. Previous research has highlighted the significant contribution of nonagricultural sources, particularly fossil fuel emissions, to urban NH levels. However, there is limited assessment of NH dynamics in suburban areas. This study focuses on four suburban sites in Beijing, covering a 16 to 22-month observation period, to investigate spatial and temporal patterns of NH concentrations. The δN-stable isotope method is employed to identify NH sources and their contributions. Our results demonstrate that agricultural sources (53 %) dominate atmospheric NH emissions in suburban areas of Beijing, surpassing nonagricultural sources, and primarily emanate from local sources. Notably, fertilizer application (37 ± 11 %) and livestock breeding (32 ± 6 %) emerge as the primary contributors in summer and spring, respectively, leading to significantly elevated NH concentrations during these seasons. Even in autumn and winter, both agricultural (49 %) and nonagricultural (51 %) sources contribute almost equally to NH emissions. This study emphasizes the need for coordinated efforts to control atmospheric NH pollution in Beijing City, with particular attention to addressing both vehicular and agricultural emissions.