Received: 03 Mar 2016 – Accepted for review: 08 Mar 2016 – Discussion started: 08 Mar 2016
Abstract. Using isotope mixing model (IsoSource) and natural δ15N method, this study evaluated contributions of major sources to N of PM2.5 at Beijing (collected during a severe haze episode of January 22nd–30th, 2013) and a background site (Menyuan, Qinghai province; collected from September to October of 2013) of China. At Beijing, δ15N values of PM2.5 (−4.1 – +13.5 ‰; mean = +2.8 ± 6.4 ‰) distributed within the range reported for major anthropogenic sources (including NH3 and NO2 from coal combustion, vehicle exhausts and domestic wastes/sewage). However, δ15N values of PM2.5 at the background site (+8.0 – +27.9 ‰; mean = +18.5 ± 5.8 ‰) were significantly higher than that of potential sources (including NH3 and NO2 from biomass burning, animal wastes, soil N cycle, fertilizer application, and organic N of soil dust). Evidences from molecular ratios of NH4+ to NO3− and/or SO42− in PM2.5, NH3 to NO2 and/or SO2 in ambient atmosphere suggested that the equilibrium of NH3 ↔ NH4 + caused apparent 15N enrichment only in NH4 + of PM2.5 at the background site due to more abundant NH3 than SO2 and NO2. Therefore, a net 15N enrichment (33 ‰) was assumed for NH3 sources of background PM2.5 when fractional contributions were estimated by IsoSource model. Results showed that 41 %, 30 % and 14 % of N in PM2.5 of Beijing originated from coal combustion, vehicle exhausts and domestic wastes/sewage, respectively. Background PM2.5 derived N mainly from biomass burning (58 %), animal wastes (15 %) and fertilizer application (9 %). These results revealed the regulation of the stoichiometry between ammonia and acidic gases on δ15N signals in PM2.5. Emissions of NO2 from coal combustion and NH3 from urban transportation should be strictly controlled to advert the risk of haze episodes in Beijing.
How to cite. Wang, Y.-L., Liu, X.-Y., Song, W., Yang, W., Han, B., Dou, X.-Y., Zhao, X.-D., Song, Z.-L., Liu, C.-Q., and Bai, Z.-P.: Isotopic partitioning of nitrogen in PM2.5 at Beijing and a background site of China, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2016-187, 2016.