Nitrogen isotopic characteristics of aerosol ammonium in a Chinese megacity indicate the reduction from vehicle emissions during the lockdown period

Zhengjie Li; Hongwei Xiao; Wendell W Walters; Meredith G Hastings; Juan Min; Linlin Song; Weizhi Lu; Libin Wu; Wende Yan; Shuguang Liu; Yunting Fang

doi:10.1016/j.scitotenv.2024.171265

Nitrogen isotopic characteristics of aerosol ammonium in a Chinese megacity indicate the reduction from vehicle emissions during the lockdown period

Sci Total Environ. 2024 Apr 20:922:171265. doi: 10.1016/j.scitotenv.2024.171265. Epub 2024 Feb 28.

Authors

Zhengjie Li¹, Hongwei Xiao², Wendell W Walters³, Meredith G Hastings⁴, Juan Min¹, Linlin Song⁵, Weizhi Lu¹, Libin Wu⁶, Wende Yan¹, Shuguang Liu⁷, Yunting Fang⁸

Affiliations

¹ 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.
² School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai 200240, China.
³ Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA.
⁴ Institute at Brown for Environment and Society, Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA.
⁵ CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China; Key Laboratory of Stable Isotope Techniques and Applications, Liaoning Province 110016, China.
⁶ Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China.
⁷ 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. Electronic address: shuguang.liu@yahoo.com.
⁸ CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China; Key Laboratory of Stable Isotope Techniques and Applications, Liaoning Province 110016, China; Qingyuan Forest CERN, Chinese Academy of Sciences, Shenyang, Liaoning 110016, China. Electronic address: fangyt@iae.ac.cn.

PMID: 38417516
DOI: 10.1016/j.scitotenv.2024.171265

Abstract

The role of agricultural versus vehicle emissions in urban atmospheric ammonia (NH₃) remains unclear. The lockdown due to the outbreak of COVID-19 provided an opportunity to assess the role of source emissions on urban NH₃. Concentrations and δ¹⁵N of aerosol ammonium (NH₄⁺) 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 NH₄⁺ concentrations, significantly lower δ¹⁵N-NH₄⁺ was found in 2020 (0.6 ± 1.0‰ in PM_2.5 and 1.4 ± 2.1‰ in PM₁₀) than in 2017 (15.2 ± 6.7‰ in PM_2.5), which indicates the NH₃ from vehicle emissions has decreased by∼50% during the lockdown while other source emissions are less affected. Moreover, a reversed seasonal pattern of δ¹⁵N-NH₄⁺ 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 δ¹⁵N-NH₄⁺ and the importance of vehicle emissions to urban atmospheric NH₃, providing conclusive evidence that reducing vehicle NH₃ emissions could be an effective strategy to reduce PM_2.5 in Chinese megacities.

Keywords: Ammonia; COVID-19 lockdown; Emission regulations; Nitrogen isotopes; Urban aerosol; Vehicle emissions.

MeSH terms

Air Pollutants* / analysis
Ammonia / analysis
Ammonium Compounds* / analysis
China
Environmental Monitoring
Nitrogen Isotopes / analysis
Particulate Matter / analysis
Respiratory Aerosols and Droplets
Vehicle Emissions

Substances

Ammonium Compounds
Nitrogen Isotopes
Vehicle Emissions
Air Pollutants
Ammonia
Particulate Matter