Delhi, the capital city of India, experiences severe air pollution and suffers from its adverse effects on human health and ecosystems. This pollution is characterized by high levels of pollutants, including atmospheric nitrogen in both the gaseous and particulate phases. However, there is a lack of simultaneous measurement of chemical composition, tracers and N data in aerosols to understand the influence of different sources on N aerosols over Delhi. Here, we measured total nitrogen (TN), water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), and N stable isotope compositions (δN) in PM samples covering the post-monsoon, winter, and summer periods of the year 2018–19. NH-N was the major N species, accounting for an average 58% of TN and 68% of WSIN. The temporal variations of TN, WSTN, NH-N, NO-N, and WSON showed peaks in the post-monsoon and winter seasons, exhibiting seasonality similar to PM and levoglucosan (a biomass-burning tracer) indicating their co-genetic sources. Based on the correlation analysis between δN and N-species, we identified two distinct secondary chemical processes: i) in an NH-poor atmosphere, the gas-to-particle (NH → NH) conversion and subsequent formation of NHHSO was the main process controlling the N and nitrogen enrichments in PM; whereas ii) under NH-rich conditions, the formation and dissociation of NHNO dominated. The coupled HYSPLIT and PSCF analyses highlighted the transport and contributions of open biomass burning emissions under a northwesterly atmospheric flow during post-monsoon as well as from local biomass combustion (from cooking and heating) during winter in the city and its vicinity. Our results suggested that i) both NH-N and NO-N were mainly impacted by biomass combustion during post-monsoon and winter seasons, and ii) NO-N resulted of dust transport from the Thar Desert in the summer season, but not NH-N. Finally, we recommend that future research focuses on the study of the seasonality of atmospheric nitrogen composition using N data from their different sources to design tailor-made measures and policies regarding the different potential sources, combining them within a comprehensive framework to ultimately improve air quality and the living environment in Delhi.

中文翻译：

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印度新德里的氮气溶胶：形态、形成和来源

印度首都德里空气污染严重，对人类健康和生态系统造成不利影响。这种污染的特点是污染物含量高，包括大气中气态和颗粒态的氮。然而，缺乏对气溶胶中化学成分、示踪剂和氮数据的同步测量，以了解不同来源对德里上空氮气溶胶的影响。在这里，我们测量了季风后、冬季和夏季 PM 样品中的总氮 (TN)、水溶性总氮 (WSTN)、水溶性无机氮 (WSIN) 和氮稳定同位素组成 (δN) 2018-19 年度。 NH-N是主要的氮形态，平均占TN的58%和WSIN的68%。 TN、WSTN、NH-N、NO-N 和 WSON 的时间变化在季风后和冬季出现峰值，表现出与 PM 和左旋葡聚糖（生物量燃烧示踪剂）类似的季节性，表明它们的共生来源。基于 δN 和 N 物种之间的相关性分析，我们确定了两个不同的二次化学过程：i）在缺乏 NH 的大气中，气体到颗粒（NH → NH）的转化和随后形成 NHHSO 是主要过程控制PM中氮和氮的富集度；而ii)在富含NH的条件下，NHNO的形成和解离占主导地位。 HYSPLIT 和 PSCF 的耦合分析强调了季风后西北大气流下露天生物质燃烧排放的传输和贡献，以及城市及其附近地区冬季当地生物质燃烧（来自烹饪和取暖）的排放。我们的结果表明，i) NH-N 和 NO-N 主要受到季风后和冬季生物质燃烧的影响，ii) NO-N 是夏季塔尔沙漠沙尘输送的影响，但 NH 不是-N。最后，我们建议未来的研究重点是利用不同来源的氮数据来研究大气氮成分的季节性，针对不同潜在来源设计量身定制的措施和政策，将它们结合在一个综合框架内，最终改善空气质量以及德里的生活环境。