National Engineering Laboratory for Applied Technology of Forestry & Ecology in Southern China, College of Biological Science and Technology, Central South University of Forestry and Technology, Changsha, Hunan 410004, China.
School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, China.
Sci Total Environ. 2024 Apr 20;922:171265. doi: 10.1016/j.scitotenv.2024.171265. Epub 2024 Feb 28.
The role of agricultural versus vehicle emissions in urban atmospheric ammonia (NH) remains unclear. The lockdown due to the outbreak of COVID-19 provided an opportunity to assess the role of source emissions on urban NH. Concentrations and δN of aerosol ammonium (NH) were measured before (autumn in 2017) and during the lockdown (summer, autumn, and winter in 2020), and source contributions were quantified using SIAR. Despite the insignificant decrease in NH concentrations, significantly lower δN-NH was found in 2020 (0.6 ± 1.0‰ in PM and 1.4 ± 2.1‰ in PM) than in 2017 (15.2 ± 6.7‰ in PM), which indicates the NH from vehicle emissions has decreased by∼50% during the lockdown while other source emissions are less affected. Moreover, a reversed seasonal pattern of δN-NH during the lockdown in Changsha has been revealed compared to previous urban studies, which can be explained by the dominant effect of non-fossil fuel emissions due to the reductions of vehicle emissions during the lockdown period. Our results highlight the effects of lockdown on aerosol δN-NH and the importance of vehicle emissions to urban atmospheric NH, providing conclusive evidence that reducing vehicle NH emissions could be an effective strategy to reduce PM in Chinese megacities.
农业和机动车排放对城市大气氨（NH）的作用仍不清楚。由于 COVID-19 爆发而实施的封锁为评估源排放对城市 NH 的作用提供了机会。在封锁之前（2017 年秋季）和期间（2020 年夏季、秋季和冬季）测量了气溶胶铵（NH）的浓度和 δN，并使用 SIAR 量化了源贡献。尽管 NH 浓度没有明显下降，但 2020 年的 δN-NH 明显较低（PM 中为 0.6 ± 1.0‰，PM 中为 1.4 ± 2.1‰），低于 2017 年（PM 中为 15.2 ± 6.7‰），这表明封锁期间机动车排放的 NH 减少了约 50%，而其他源排放的影响较小。此外，与以前的城市研究相比，封锁期间长沙的 δN-NH 呈现出相反的季节性模式，这可以用封锁期间机动车排放减少导致非化石燃料排放的主导作用来解释。我们的结果强调了封锁对气溶胶 δN-NH 的影响，以及机动车排放对城市大气 NH 的重要性，为减少车辆 NH 排放可以成为减少中国特大城市 PM 的有效策略提供了确凿证据。
