Abstract. Stable nitrogen isotopic composition (δ¹⁵N) has proven to be a valuable tool for identifying sources of nitrates (NO₃^–) in PM_2.5. However, the absence of a systematic study on the δ¹⁵N values of domestic NOx sources hinders accurate identification of NO₃^– sources in China. Here, we systematically determined and refined δ¹⁵N values for six categories of NOx sources in the local Tianjin area using an active sampling method. Moreover, the δ¹⁵N values of NO₃^– in PM_2.5 were measured during pre-heating, mid-heating and late-heating periods, which are the most heavily polluted in Tianjin. Results shown that the representative nature and region-specific characteristics of isotopic fingerprints for six categories of NOx sources in Tianjin. The Bayesian isotope mixing (MixSIAR) model demonstrated that coal combustion, biomass burning, and vehicle exhaust collectively contributed more than 60 %, dominating the sources of NO₃^– during sampling periods in Tianjin. However, failure to consider the isotopic signatures of local NOx sources could result in an underestimation of the contribution from coal combustion. Additionally, the absence of industrial sources, an uncharacterized source in previous studies, may directly result in the contribution fraction of other sources being overestimated by the model more than 15 %. Notably, as the number of sources input to the model increased, the contribution of various NOx sources was becoming more stable, and the inter-influence between various sources significantly reduced. This study demonstrated that the refined isotopic fingerprint in a region-specific context could more effectively distinguish source of NO₃^–, thereby providing valuable insights for controlling NO₃^– pollution.

中文翻译：

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技术说明：精炼局部 NOx 的 δ15N 同位素指纹，以准确识别 PM2.5 中硝酸盐的来源


摘要。稳定氮同位素组成 (δ ¹⁵ N) 已被证明是识别 PM _2.5 ^– ) 来源的宝贵工具。 /b3> .然而，由于缺乏对国内NOx源δ ¹⁵ N值的系统研究，阻碍了我国NO ₃ ^– 源的准确识别。在此，我们采用主动采样的方法，系统地测定并细化了天津地区六类NOx源的δ ¹⁵ N值。此外，还测量了PM _2.5 中NO ₃ ^– 的δ ¹⁵ N值，并在预热、加热中期和后期进行了测量。 -供暖期是天津污染最严重的时期。结果表明，天津市六类NOx源同位素指纹图谱具有代表性和区域特征。贝叶斯同位素混合（MixSIAR）模型表明，煤炭燃烧、生物质燃烧和汽车尾气合计贡献超过60%，是天津采样期间NO ₃ ^– 的主要来源。然而，如果不考虑当地氮氧化物源的同位素特征，可能会导致低估煤炭燃烧的贡献。此外，工业源的缺失（先前研究中未表征的源）可能会直接导致模型高估其他源的贡献比例超过15%。值得注意的是，随着输入模型的源数量增加，各种NOx源的贡献变得更加稳定，并且各种源之间的相互影响显着减少。 本研究表明，在特定区域背景下精制的同位素指纹可以更有效地区分 NO ₃ ^– 的来源，从而为控制 NO ₃ 提供有价值的见解。 ^– 污染。