Institute for Environmental and Climate Research, Jinan University, Guangzhou, China; Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou, China.
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China; Guangzhou Sub-branch of Guangdong Ecological and Environmental Monitoring Center, Guangzhou, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China; CAS Center for Excellence in Deep Earth Science, Guangzhou, China; University of Chinese Academy of Sciences, Beijing, China.
Sci Total Environ. 2022 Nov 20;848:157750. doi: 10.1016/j.scitotenv.2022.157750. Epub 2022 Aug 1.
Ammonia (NH) is the most prevalent alkaline gas in the atmosphere and plays a critical role in air pollution and public health. However, scientific debate remains over whether agricultural emissions (e.g., livestock and fertilizer application) dominate NH in urban atmosphere in China, which is one of the largest NH emitters in the world. In this study, we first simultaneously collected the fine atmospheric particles (PM) at two heights (ground and 488 m) using the atmospheric observatories in Canton Tower, Guangzhou city, China for the measurements of stable nitrogen isotope composition in ammonium (δN-NH). Our results showed that the average δN-NH value at the ground and the 488 m observatory were 16.9 ‰ and 3.8 ‰, respectively, implying that NH aerosols between the two heights probably have different sources. Moreover, we found that the δN-NH value would sharply decrease to -16.7 ‰ when the air masses came from western Guangzhou, where the urbanization is limited compared to other surrounding areas. The Bayesian mixing model indicated that NH aerosol at the ground observatory was mainly derived from non-agricultural activities (76 %, e.g., vehicular exhaust), with the rest from agricultural sources (24 %). As for the 488 m observatory, the contribution of non-agricultural sources was 53 %, which is lower than the ground observatory. This is expected as the lower air receives more impacts from the local urban emission. However, the current "bottom-up" emission inventory illustrates that only ~20 % NH in Guangzhou is associated with non-agricultural emissions, which is significantly lower than our δN-based results. Overall, our findings strongly imply that non-agricultural sources dominate the urban NH in Guangzhou or maybe in adjacent cities of the Pearl River Delta region as well, suggesting that the emission inventory of NH in this region probably is urgently needed to be revisited in future studies.
氨（NH）是大气中最普遍的碱性气体，在空气污染和公共健康方面发挥着关键作用。然而，科学界仍在争论农业排放（例如牲畜和化肥施用）是否主导了中国城市大气中的 NH，中国是世界上最大的 NH 排放国之一。在这项研究中，我们首先使用中国广州 Canton Tower 的大气观测站在两个高度（地面和 488 米）同时收集细颗粒大气颗粒物（PM），以测量铵中的稳定氮同位素组成（δN-NH）。我们的结果表明，地面和 488 米观测站的平均 δN-NH 值分别为 16.9‰和 3.8‰，这意味着两个高度之间的 NH 气溶胶可能有不同的来源。此外，我们发现当空气团来自城市化程度低于其他周边地区的广州西部时，δN-NH 值会急剧下降到-16.7‰。贝叶斯混合模型表明，地面观测站的 NH 气溶胶主要来自非农业活动（76%，例如车辆尾气），其余来自农业源（24%）。对于 488 米观测站，非农业源的贡献为 53%，低于地面观测站。这是意料之中的，因为低空更受当地城市排放的影响。然而，当前的“自上而下”排放清单表明，广州只有约 20%的 NH 与非农业排放有关，这明显低于我们基于 δN 的结果。总的来说，我们的研究结果强烈表明，非农业源主导了广州或可能是珠江三角洲地区其他城市的城市 NH，这表明该地区 NH 的排放清单在未来研究中可能需要重新修订。
