Nitrate has long been focused due to its dominant proportion in PM_2.5. In this study, PM_2.5 samples were non-consecutively collected in a coastal city located in Western Pacific from March 6, 2019 to January 16, 2020. On the basis of the determination of water soluble inorganic ions and nitrogen and oxygen isotopic signatures of nitrate, its formation pathways were estimated by isotope fractionation calculation and NO_x source contributions were quantified with stable isotope analysis in R (SIAR) model. Results showed that δ¹⁵N-NO₃⁻ ranged from −3.7‰ to 32.1‰, and δ¹⁸O-NO₃⁻ varied from 38.1‰ to 101.4‰. Nitrate formation was dominated by oxidation of NO₂ with hydroxyl radical (OH) in spring, summer, and fall, while it was mainly controlled by N₂O₅ heterogeneous hydrolysis in winter. Quantitative analysis of NO_x sources contributing to nitrate by using SIAR model showed that estimated annual average contributions from diesel vehicle emission, gasoline vehicle emission, biogenic soil emission, biomass burning, and coal combustion were 25.6%, 21.4%, 21.1%, 17.4%, and 14.5%, respectively. The control of diesel vehicle emission is vital to nitrate reduction and air quality improvement in spring, summer, and fall, while coal combustion is the primary NO_x source to nitrate in winter. Posterior distribution of source contribution results from SIAR model presented more stable results in spring.

长期以来，硝酸盐因其在 PM _2.5中占主导地位而备受关注。本研究于 2019 年 3 月 6 日至 2020 年 1 月 16 日在位于西太平洋的一个沿海城市非连续采集 PM _2.5样品。在测定水溶性无机离子和硝酸盐氮氧同位素特征的基础上，通过同位素分馏计算估计其形成途径，并通过R（SIAR）模型中的稳定同位素分析量化NO _{x源贡献。}结果表明，δ ¹⁵ N-NO ₃ ^-范围为-3.7‰～32.1‰，δ ¹⁸ O-NO ₃ ^-从 38.1‰ 到 101.4‰ 不等。硝酸盐的生成在春季、夏季和秋季以羟基自由基（OH）氧化NO _{2为主，冬季主要以N 2} O ₅非均相水解控制。用SIAR模型定量分析NO _x对硝酸盐的贡献率表明，柴油车排放、汽油车排放、生物土壤排放、生物质燃烧和煤炭燃烧的年平均贡献分别为25.6%、21.4%、21.1%、17.4%和 14.5%，分别。控制柴油车排放对春夏秋季硝酸盐减少和空气质量改善至关重要，而燃煤是主要的_NOx冬季硝酸盐的来源。SIAR 模型的源贡献结果的后验分布在春季呈现出更稳定的结果。