资源环境科技发展态势分析平台

With the increasingly severe ozone pollution in the Beijing-Tianjin-Hebei region in recent years, NO₂ photolysis has attracted our attention as the main source of tropospheric ozone generation. The photolysis rate of NO₂ (J(NO₂)) is of great importance for the quantification of photochemical ozone generation and photochemical pollution research, but its long-term changes in the Beijing-Tianjin-Hebei region remain unclear. An efficient reconstruction method for J(NO₂) was established via simulations with the troposphere ultraviolet and visible radiation (TUV) model and the observations of J(NO₂) and total ultraviolet (UV) radiation at a typical suburban site in the Beijing-Tianjin-Hebei region. We introduced the cloud modification factor in this method which improved the R² value between the calculated and observed J(NO₂) values from 0.64 to 0.94 over the TUV clear-sky simulation level. A long-term (2005–2019) J(NO₂) dataset in Xianghe was reconstructed by applying this method. The annual mean J(NO₂) value reached 3.5*10⁻³ s⁻¹ from2005 to 2019. The annual mean J(NO₂) value fluctuated slightly from 2005 to 2012 but increased evidently in the last 7 years. The increase rates of the annual mean J(NO₂) value and O(³P) generation via NO₂ photolysis were 1.3*10⁻⁴ s⁻¹ per year and 1.1*10⁻³ ppb•s⁻¹ per year, respectively, from 2013 to 2019. From 2005 to 2019, J(NO₂) exhibited the sharpest increasing trend in summer, but increased the least in spring. The monthly mean J(NO₂) value was the highest in May and the lowest in November. Our results demonstrated that to control the ozone concentration in the Beijing-Tianjin-Hebei region, we must pay more attention to the reduction in volatile organic compounds (VOCs) under the year-by-year increase in ambient J(NO₂).