The influence of aerosols on the NO2 photolysis rate in a suburban site in North China

The photolysis of NO₂ is an important driving force of tropospheric ozone. The intensity of this photolysis reaction affects atmospheric oxidation and photochemical pollution process. Photolysis rate of nitrogen dioxide (JNO₂) is affected by aerosols, temperature, solar zenith angle (SZA), clouds, and so on. Among them, aerosol is an important influencing factor because of its complicated and irregular change; aerosol quantitative effect on JNO₂ is constructive for the coordinated control of O₃ and particulate matter. In order to quantitatively assess the impact of aerosols on JNO₂ in the long-term, the reconstructed JNO₂ data in a suburban site in North China from 2005 to 2019 are used. We found that JNO₂ and aerosol optical depth (AOD) presented logarithmic relations under different solar zenith angle (SZA) levels, the aerosol attenuation effect on JNO₂ decreased as AOD increased. Two main influencing factors of JNO₂, SZA, and AOD, were fitted into a quadratic polynomial to quantify the AOD effect on JNO₂. The results showed that the average annual AOD effect on JNO₂ in Xianghe from 2005 to 2019 was -28.6% compared to an aerosol free atmosphere; the seasonal mean AOD effect in spring, summer, autumn, and winter was -27.1% and -35.1%, -25.5% and -26.3%, respectively. During the study period, JNO₂ increased with an average of 5 × 10^-5 s^-1 per year, while the annual average aerosol optical depth (AOD) was 0.80 ± 0.10, showing an overall downward trend. Annual mean AOD attenuation effect on JNO₂ decreased over time; the decreases were larger in spring and summer, and smaller in autumn and winter.