- 1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
- 2International Joint Laboratory for Regional Pollution Control, Ministry of Education, Beijing 100816, China
- 3Institute of Environmental Physics (IUP-UB), University of Bremen, Bremen, Germany
- 4Sichuan Academy of Environmental Policy and Planning, Chengdu 610041, China
- 5Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, School of Environmental Science and Engineering, Nanjing University of Information Sci
- 6Key Laboratory for Urban Habitat Environmental Science and Technology, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen 518055, China
- 7State Key Laboratory of Regional Air Quality Monitoring, Guangdong Key Laboratory of Secondary Air Pollution Research, Guangdong Environmental Monitoring Center, Guangzhou 510308, China
- 8Center of Marine Environmental Science (MARUM), University of Bremen, Germany
- 9Climate and Atmosphere Research Center (CARE-C), The Cyprus Institute, Nicosia, Cyprus
- 10Environmental Chemical Processes Laboratory (ECPL), Department of Chemistry, University of Crete, Heraklion, Greece
- 11Environmental Modeling Group, Max Planck Institute for Meteorology, Hamburg, Germany
- 12Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA
PM2.5 pollution poses a serious threat to human health, making its mitigation a priority for policymakers. Over the last decade, air quality control measures have led to significant reductions in PM2.5 concentrations across China. However, meteorological changes driven by variations in the climate system can offset these effects and even exacerbate PM2.5 pollution. During the cold seasons (autumn and winter) of 2015-2017, PM2.5 pollution persisted in the Pearl River Delta (PRD), South China, despite rapid emission reductions both in the PRD and its upwind regions. This period coincided with a notable transition in ENSO state, from a very strong El Niño in 2015 to a weak-to-moderate La Niña in 2017. Through meteorological analysis and WRF/CMAQ simulations, this study investigates the connection between this climate transition and persisted PM2.5 pollution in the PRD. Comparisons of meteorological conditions during the three cold seasons align with previously reported El Niño and La Niña effects: Precipitation and polluted-day humidity reached the highest in the El Niño year (2015), while a northerly wind anomaly was observed in the La Niña year (2017). These meteorological changes weakened local PM2.5 production but enhanced PM2.5 transport to the PRD in the three cold seasons, as indicated by changing contributions to PM2.5 in the WRF/CMAQ simulations: The contributions of local emissions declined from 30% in 2015 to 22% in 2017, while the contributions of upwind emissions rose from 48% to 56%. Although emission reductions contributed to lower polluted-day PM2.5 concentration in the PRD by -5.7 µg/m3 in 2015-2016 and -2.7 µg/m3 in 2016-2017, this effect was outweighed by the influence of meteorological changes, which resulted in its reduction of -6.1 µg/m3 in 2015-2016 and increase of +10.7 µg/m3 in 2016-2017. Three-year changes in PM2.5 sulfate were mainly attributed to emission reduction in the upwind regions, while these in PM2.5 nitrate were linked to varying transport contributions under meteorological changes. This study indicates that to effectively mitigate PM2.5 pollution in the PRD, targeted strategies that focus on local or upwind emissions under varying meteorological conditions should be adopted.
Acknowledgement: This work was supported by the National Key Research and Development Program of China (grant No. 2018YFC0213204),the National Science and Technology Pillar Program of China (grant No. 2014BAC21B01), the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany´s Excellence Strategy (University Allowance, EXC 2077, University of Bremen) and co-funded DFG-NSFC Sino-German Air-Changes project (grant no. 448720203).
How to cite: Qu, K., Wang, X., Yan, Y., Jin, X., He, L.-Y., Huang, X.-F., Cai, X., Shen, J., Peng, Z., Xiao, T., Vrekoussis, M., Kanakidou, M., Brasseur, G., Daskalakis, N., Zeng, L., and Zhang, Y.: Why did PM2.5 pollution persist in the Pearl River Delta, South China during the El Niño–La Niña transition despite emission reductions?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8633, https://doi.org/10.5194/egusphere-egu25-8633, 2025.
