Spatiotemporal characterization of aerosols and trace gases over the Yangtze River Delta region, China: impact of trans-boundary pollution and meteorology

Zeeshan Javed; Muhammad Bilal; Zhongfeng Qiu; Guanlin Li; Osama Sandhu; Khalid Mehmood; Yu Wang; Md Arfan Ali; Cheng Liu; Yuhang Wang; Ruibin Xue; Daolin Du; Xiaojun Zheng

doi:10.1186/s12302-022-00668-2

Spatiotemporal characterization of aerosols and trace gases over the Yangtze River Delta region, China: impact of trans-boundary pollution and meteorology

Environ Sci Eur. 2022;34(1):86. doi: 10.1186/s12302-022-00668-2. Epub 2022 Sep 8.

Authors

Zeeshan Javed^#¹, Muhammad Bilal^#², Zhongfeng Qiu², Guanlin Li¹, Osama Sandhu³, Khalid Mehmood⁴, Yu Wang², Md Arfan Ali², Cheng Liu^{5

6

7

8}, Yuhang Wang⁹, Ruibin Xue¹⁰, Daolin Du¹, Xiaojun Zheng¹

Affiliations

¹ Institute of Environment and Ecology, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, 212013 China.
² School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing, 210044 China.
³ National Agromet Center, Pakistan Meteorological Department, Islamabad, 44000 Pakistan.
⁴ Key Laboratory of Meteorological Disaster, Ministry of Education [KLME]/Joint International Research Laboratory of Climate and Environment Change [ILCEC]/Collaborative Innovation Center On Forecast and Evaluation of Meteorological Disasters [CIC-FEMD]/CMA Key Laboratory for Aerosol-Cloud-Precipitation, Nanjing University of Information Science and Technology, Nanjing, 210044 China.
⁵ Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, 230026 China.
⁶ Key Laboratory of Environmental Optics & Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, 230031 China.
⁷ Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021 China.
⁸ Key Laboratory of Precision Scientific Instrumentation of Anhui Higher Education Institutes, University of Science and Technology of China, Hefei, 230026 China.
⁹ School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332 USA.
¹⁰ Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention [LAP3], Department of Environmental Science and Engineering, Fudan University, Shanghai, 200433 China.

^# Contributed equally.

Abstract

Background: The spatiotemporal variation of observed trace gases (NO₂, SO₂, O₃) and particulate matter (PM_2.5, PM₁₀) were investigated over cities of Yangtze River Delta (YRD) region including Nanjing, Hefei, Shanghai and Hangzhou. Furthermore, the characteristics of different pollution episodes, i.e., haze events (visibility < 7 km, relative humidity < 80%, and PM_2.5 > 40 µg/m³) and complex pollution episodes (PM_2.5 > 35 µg/m³ and O₃ > 160 µg/m³) were studied over the cities of the YRD region. The impact of China clean air action plan on concentration of aerosols and trace gases is examined. The impacts of trans-boundary pollution and different meteorological conditions were also examined.

Results: The highest annual mean concentrations of PM_2.5, PM₁₀, NO₂ and O₃ were found for 2019 over all the cities. The annual mean concentrations of PM_2.5, PM₁₀, and NO₂ showed continuous declines from 2019 to 2021 due to emission control measures and implementation of the Clean Air Action plan over all the cities of the YRD region. The annual mean O₃ levels showed a decline in 2020 over all the cities of YRD region, which is unprecedented since the beginning of the China's National environmental monitoring program since 2013. However, a slight increase in annual O₃ was observed in 2021. The highest overall means of PM_2.5, PM₁₀, SO₂, and NO₂ were observed over Hefei, whereas the highest O₃ levels were found in Nanjing. Despite the strict control measures, PM_2.5 and PM₁₀ concentrations exceeded the Grade-1 National Ambient Air Quality Standards (NAAQS) and WHO (World Health Organization) guidelines over all the cities of the YRD region. The number of haze days was higher in Hefei and Nanjing, whereas the complex pollution episodes or concurrent occurrence of O₃ and PM_2.5 pollution days were higher in Hangzhou and Shanghai.The in situ data for SO₂ and NO₂ showed strong correlation with Tropospheric Monitoring Instrument (TROPOMI) satellite data.

Conclusions: Despite the observed reductions in primary pollutants concentrations, the secondary pollutants formation is still a concern for major metropolises. The increase in temperature and lower relative humidity favors the accumulation of O₃, while low temperature, low wind speeds and lower relative humidity favor the accumulation of primary pollutants. This study depicts different air pollution problems for different cities inside a region. Therefore, there is a dire need to continuous monitoring and analysis of air quality parameters and design city-specific policies and action plans to effectively deal with the metropolitan pollution.

Supplementary information: The online version contains supplementary material available at 10.1186/s12302-022-00668-2.

Keywords: China’s clean air action plan; National Ambient Air Quality Standards; Ozone; Particulate matter; TROPOMI; Yangtze River Delta region.