DataSheet1_Developing Nitrogen Isotopic Source Profiles of Atmospheric Ammonia for Source Apportionment of Ammonia in Urban Beijing.docx

Atmospheric ammonia (NH3) is the key precursor in secondary particle formation, which is identified as the most abundant components of haze in Beijing in most cases. It is critical to understand the characteristics of NH3 from various emission sources and quantify each source contribution to NH3 in ambient atmosphere. Stable nitrogen (N) isotope composition (δ15N) is an effective tool to study NH3 source. However, this tool cannot be effectively applied in Beijing due to the lack of comprehensive N nitrogen isotope source profiles. Reliable source profiles are the basis of source apportionment of NH3 using the isotope mixing model. In this study, multiple NH3 source samples were collected at sites, representing six major NH3 source types in Beijing from 2017 to 2018 in four seasons. The δ15N values of 212 NH3 source samples were determined to build a local source profiles database of δ15N. NH3 from traffic source presents significantly higher δ15N values (−14.0 ± 5.4‰), distinguished from other sources. The δ15N values of other sources besides traffic were more depleted and did not clear differences (solid waste, sewage, human feces, fertilizer, and livestock for −33.6 ± 4.5‰, −34.1 ± 4.8‰, −32.2 ± 3.8‰, −35.0 ± 3.9‰, and −34.9 ± 4.4‰, respectively). These sources were classified into non-traffic source in this study. From March 2018 to March 2019, ambient NH3 samples were collected at an urban site in Beijing. With the newly developed source profiles in this study, the contribution of traffic and non-traffic sources to ambient NH3 in an urban site in Beijing was calculated using 15N isotope mass balance equations. Traffic and non-traffic sources contributed 8% and 92% to ambient NH3 in urban Beijing, respectively. The highest seasonal average contribution of traffic to ambient NH3 was found in winter (22%). Our results reveal the importance of traffic source and provide evidence for the need to control NH3 emission from traffic in urban Beijing in winter.

大气氨（NH3）是次生粒子形成的关键前体物质，通常情况下，其在北京雾霾中的含量最为丰富。深入了解不同排放源中NH3的特性，并量化每种源对环境大气中NH3的贡献至关重要。稳定氮同位素组成（δ15N）是研究NH3源的有效手段。然而，由于缺乏全面的N氮同位素源谱，该工具在北京地区无法有效应用。可靠的源谱是利用同位素混合模型进行NH3源分配的基础。在本研究中，于2017年至2018年间四个季节内，于多个地点收集了代表北京六种主要NH3源类型的多个NH3源样品。通过测定212个NH3源样品的δ15N值，构建了一个本地的δ15N源谱数据库。来自交通源的NH3呈现出显著更高的δ15N值（−14.0 ± 5.4‰），与其他源区分开来。除交通源之外的其他源的δ15N值较为贫乏，且差异不明显（分别为固体废物、污水、人粪、肥料和家畜的δ15N值为−33.6 ± 4.5‰、−34.1 ± 4.8‰、−32.2 ± 3.8‰、−35.0 ± 3.9‰和−34.9 ± 4.4‰）。这些源在本研究中被归类为非交通源。从2018年3月到2019年3月，在北京一个城市站点收集了环境NH3样品。利用本研究新开发的源谱，利用15N同位素质量平衡方程计算了交通源和非交通源对北京城市站点环境NH3的贡献。交通源和非交通源分别贡献了环境NH3的8%和92%。交通源对环境NH3的最高季节平均贡献出现在冬季（22%）。我们的研究结果揭示了交通源的重要性，并为北京城市冬季控制交通源NH3排放提供了证据。