Understanding Regional Background Ozone by Multiple Methods: A Case Study in the Shandong Region, China, 2018–2020

Abstract

Uprising ground‐level ozone (O3) 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 O3 concentrations. To quantify the regional background O3 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 O3 pollution occurred frequently yet the background contributions have not been well quantified. We used four methods to quantify the regional background O3: Method 1 is PCA analysis with only ambient O3 data as input; Method 2 is PCA analysis considering O3 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 O3 measured to represent regional background O3 concentrations. Results derived from multiple methods show an overall consistent trend with 2018–2020 averaged regional background O3 (MDA8) of 41.5 ppb, accounting for 79.4% of the total O3 in the region. From 2018 to 2020, the changes in regional MDA8 O3 estimated by Methods 1–4 are −1.8, 0.7, −2.4, and 0.4 ppb, respectively. Clear seasonal variations in the regional background O3 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 O3 contribution gradually increasing from coastal areas to inland areas. The 3‐year average sea‐land breeze contribution to summertime O3 in the eastern coastal cities was estimated to be around 2.1%, while the local photochemistry to O3 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.

Analysis of Ozone Pollution Characteristics, Meteorological Effects, and Transport Sources in Zhuzhou, China

“…This phenomenon occurs mainly because concentrations in summer are lower due to consumption as an O 3 precursor, while the high concentrations in winter are due to greater consumption of fossil fuels and the tendency to have an inverse thermosphere and stable atmospheric boundary layer in winter [22], which limit the convective diffusion of several pollutants. The photochemical reaction process can be explained by Equations ( 1)-( 3) [23]. The main process is the oxidation of NO by atmospheric oxidants to produce NO 2 and the photolysis of NO 2 to produce O 3 .…”

“…O 3 pollution was influenced by temperature, relative humidity, NO x , wind direction, wind speed, and was also related to local emissions and regional transport, as well as photochemical reactions carried out by O 3 precursors during transport [23]. To clarify the transport channels of O 3 in Zhuzhou City, the city monitoring station sites with the highest number of O 3 exceedance days in 2021 were selected for transport analysis and cluster analysis of the days polluted by O 3 in September using a backward trajectory model.…”