Understanding Regional Background Ozone by Multiple Methods: A Case Study in the Shandong Region, China, 2018–2020
Fengyun Wang, Hong Zhang, Jianfu Xue, Ling Huang, Y. J. Wang, Hui Chen, S. Y. Wang, Joshua S. Fu, Li Li
Abstract
Abstract Uprising ground‐level ozone (O 3 ) and its regional pollution in Northern China are attracting more attention. Besides local precursor emissions and photochemistry, background ozone and long‐range transport also contribute significantly to O 3 concentrations. To quantify the regional background O 3 concentrations and their temporal and spatial variations, multiple methods, including the principal component analysis (PCA) and the Texas Commission on Environmental Quality (TCEQ) method, were applied as a case study in Shandong province in Northern China, where serious O 3 pollution occurred frequently yet the background contributions have not been well quantified. We used four methods to quantify the regional background O 3 : Method 1 is PCA analysis with only ambient O 3 data as input; Method 2 is PCA analysis considering O 3 and meteorological parameters; Method 3 combines multiple linear regression and the traditional PCA method; and Method 4 is based on TCEQ and consists of the lowest MAD8 O 3 measured to represent regional background O 3 concentrations. Results derived from multiple methods show an overall consistent trend with 2018–2020 averaged regional background O 3 (MDA8) of 41.5 ppb, accounting for 79.4% of the total O 3 in the region. From 2018 to 2020, the changes in regional MDA8 O 3 estimated by Methods 1–4 are −1.8, 0.7, −2.4, and 0.4 ppb, respectively. Clear seasonal variations in the regional background O 3 are observed, showing a pattern of summer > spring > autumn > winter. In addition, the regional ozone contribution at coastal cities was larger than that for inland cities with local O 3 contribution gradually increasing from coastal areas to inland areas. The 3‐year average sea‐land breeze contribution to summertime O 3 in the eastern coastal cities was estimated to be around 2.1%, while the local photochemistry to O 3 in the inland cities was about 29.7% during ozone pollution episodes, with maximum contribution estimated up to 55.8%. Overall, our study provides insights into the regional background ozone and local photochemistry in Northern China.