Yao Xiaohong, Zhang Leiming
Lab of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100, China.
Air Quality Research Division, Science and Technology Branch, Environment and Climate Change Canada, Toronto M3H 5T4, Canada.
ACS Omega. 2019 Dec 11;4(26):22133-22142. doi: 10.1021/acsomega.9b03284. eCollection 2019 Dec 24.
Decadal trends of atmospheric ammonia (NH) and their potential causes were explored through the analysis of monitored data collected at 15 sites in the United States and 7 sites in Canada. Large percentage increases in the annual average concentration of atmospheric NH, for example, >100% at 6 sites and 40-100% at 10 sites, were observed over the most recent 8-13 year period. In contrast, a decrease or a narrow variation in NH emissions was reported at the state or provincial level in both countries during the same period. Decreased emissions of SO and NO across North America in the past decade would have reduced the chemical loss of atmospheric NH to form particulate NH . Such a chemical mechanism was verified through regression analysis at about half of the monitored sites, where the increasing trends in atmospheric NH were partially explained by the reduced NH . Excluding the reduced contribution from this chemical loss to generate the adjusted annual NH concentration through two approaches, no decreasing trends can be obtained to align those in emissions at most sites, implying that other factors also contributed to the increase in the annual NH concentration. Correlation analysis results implied that enhanced drought conditions and increased ambient temperatures also likely contributed to the increasing trend in the annual NH concentration at some sites. The large percentage increases in the annual NH concentration cannot be fully explained by all the identified causes, leading to oppugning the reality of the decrease in NH emissions reported across North America in the recent decade.
通过对在美国15个地点和加拿大7个地点收集的监测数据进行分析，探讨了大气氨（NH₃）的年代际趋势及其潜在成因。在最近的8 - 13年期间，观测到大气NH₃年平均浓度大幅上升，例如，6个地点上升幅度超过100%，10个地点上升幅度在40% - 100%之间。相比之下，同期两国在州或省级层面报告的NH₃排放量有所下降或变化不大。过去十年北美地区SO₂和NOₓ排放量的减少本应降低大气NH₃形成颗粒态NH₄⁺的化学损失。通过对约一半监测站点的回归分析验证了这种化学机制，在这些站点，大气NH₃的上升趋势部分可由NH₄⁺的减少来解释。通过两种方法排除这种化学损失对调整后的年NH₃浓度贡献的减少后，在大多数站点无法得到与排放量下降趋势一致的下降趋势，这意味着其他因素也导致了年NH₃浓度的增加。相关性分析结果表明，干旱加剧和环境温度升高也可能导致了部分站点年NH₃浓度上升趋势。年NH₃浓度的大幅上升无法完全由所有已确定的原因来解释，这引发了对北美近十年报告的NH₃排放量下降真实性的质疑。
