Increased diurnal difference of NO2 concentrations and its impact on recent ozone pollution in eastern China in summer

Yang Shen, Fei Jiang, Shuzhuang Feng, Zheng Xia, Yanhua Zheng, Xiaopu Lyu, LingYu Zhang, Chenxi Lou

Research output: Contribution to journalJournal articlepeer-review

7 Citations (Scopus)


Nitrogen dioxide (NO2) is a key tropospheric O3 precursor. Since 2013, efforts to decrease air pollution in China have driven substantial declines in annual NO2 concentrations, whereas ozone (O3) concentrations have increased. Based on nationwide NO2 observations and a regional air quality model (WRF-CMAQ), we analyzed trends in the diurnal difference (DD, the difference between nighttime and daytime concentrations) of NO2 concentrations across eastern China and in five national urban agglomerations (UAs) from 2014 to 2021, and explored the factors underlying such changes and the potential impacts on O3 pollution. We found that the observed DD of NO2 has increased in most cities and UAs, and that this trend can be primarily attributed to changes in anthropogenic emissions, based on comparison with DDs simulated with fixed anthropogenic emissions, which generally showed much weaker trends and little interannual variation. A sensitivity analysis using the WRF-CMAQ model was conducted to investigate the impact of a modified diurnal cycle of nitrogen oxides (NOx) emissions on O3 concentrations. The result revealed that enhancing the DD of NO2 would increase O3 concentrations in the morning and the daily maximum 8-h O3 concentrations in the cities with high NOx concentrations, as well as downwind areas of cities, indicating that greater DDs in NO2 is one of the reasons that have led to the enhanced China's O3 pollution in recent years.

Original languageEnglish
Article number159767
JournalScience of the Total Environment
Volume858, Part 1
Publication statusPublished - 1 Feb 2023

Scopus Subject Areas

  • Pollution
  • Waste Management and Disposal
  • Environmental Engineering
  • Environmental Chemistry

User-Defined Keywords

  • Diurnal difference
  • NO2 concentrations
  • O3 pollution
  • Urban agglomeration


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