Source apportionment of atmospheric ammonia in suburban Beijing revealed through ¹⁵N-stable isotopes

Addressing the urgent issue of atmospheric ammonia (NH₃) 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 NH₃ levels. However, there is limited assessment of NH₃ 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 NH₃ concentrations. The δ¹⁵N-stable isotope method is employed to identify NH₃ sources and their contributions. Our results demonstrate that agricultural sources (53 %) dominate atmospheric NH₃ 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 NH₃ concentrations during these seasons. Even in autumn and winter, both agricultural (49 %) and nonagricultural (51 %) sources contribute almost equally to NH₃ emissions. This study emphasizes the need for coordinated efforts to control atmospheric NH₃ pollution in Beijing City, with particular attention to addressing both vehicular and agricultural emissions.