[Estimation of Regional Background Ozone in Henan Province from 2019 to 2021]

Clarifying the regional transmission and local generation contributions of ozone （O₃） is important for controlling O₃ pollution. To quantify the regional background and spatial-temporal variations of O₃, a comprehensive study was conducted using multiple methods including principal component analysis （PCA） and TCEQ, with Henan Province as a case study. Based on monitoring data from 59 national sites in Henan Province during 2019-2021, four methods were employed to estimate the regional background of O₃. Method 1 was the traditional method, performing O₃ univariate-multisite PCA analysis. Method 2 was a multivariate-single-site PCA analysis considering nitrogen dioxide and meteorological conditions as constraints. Method 3 combined PCA and multiple linear regression （MLR） to determine regional background contributions, drawing on the idea of source apportionment. Method 4 was the TCEQ method that used the lowest measured O₃-8h concentration as the regional background. The estimation results showed that Methods 1 and 2 were basically equal, and Methods 3 and 4 were approximately 37-60 μg·m^-3 lower than Method 1. From 2019 to 2021, the changes in regional background ρ（O₃-8h） estimated by Methods 1-4 were 1.6, -13.4, 5.9, and -3.5 μg·m^-3, respectively. The average estimations derived from multiple methods showed that the regional background ρ（O₃-8h） in Henan Province from 2019 to 2021 concentrations were 82.0, 79.0, and 79.7 μg·m^-3, accounting for 75.9%, 76.4%, and 78.7% of the total regional O₃-8h, respectively. The regional background O₃-8h estimated by the four methods showed obvious seasonal changes, characterized by summer > spring > fall > winter.