Combustion-driven inorganic nitrogen in PM_2.5 from a city in central China has the potential to enhance the nitrogen load of North China

Inorganic nitrogen (NH₄⁺ and NO₃^-) is a significant component of PM_2.5, influencing not only regional ecological systems but also on other regions through the migration of air masses. However, few studies have simultaneously investigated the sources of NH₄⁺ and NO₃^-, and their potential transport pathways remain poorly understood. Here, daily PM_2.5 samples were collected in Jiaozuo, a key city in the air pollution transmission channel to the north China, from 1 September to 5 December, 2017. Major water-soluble inorganic ions and the isotope compositions of NH₄⁺ and NO₃^- in PM_2.5 were analyzed. The results indicated substantial amounts of inorganic nitrogen in PM_2.5, particularly at high PM_2.5 concentrations. The Bayesian isotope mixing model (MixSIAR) results revealed that combustion sources contributed 79.5 % to NO₃^- and 51.6 % to NH₄⁺. Moreover, the medium to high potential source regions for combustion-related NH₃ is basically consistent with combustion-related NOx. Therefore, stringent regulation of combustion emissions has the potential to mitigate inorganic nitrogen pollution in PM_2.5 in Jiaozuo. The results of the forward trajectory cluster and PSCF (potential source contribution function) analysis revealed that a significant amount of combustion-driven inorganic nitrogen in PM_2.5 from Jiaozuo will transport to downwind area, particularly north China. Combustion-driven inorganic nitrogen levels carried by these air masses exceeded half the average value for cities in North China during the same period. Our study highlights that combustion emissions dominate the inorganic nitrogen sources in PM_2.5 and that substantial amounts of combustion-driven inorganic nitrogen can be transported from Jiaozuo to North China, potentially enhancing the nitrogen load in those areas.