Variation Characteristics and Estimation Method of NO₂ Photolysis Rate in Xianghe during Winter

The NO₂ photolysis frequency j(NO₂) is an important parameter in tropospheric chemistry. It is one of the key factors affecting the formation of ozone and OH radicals in the troposphere. The variations of j(NO₂) and solar radiation and the correlation between photolysis rate and sub-band solar radiation were analyzed using the observational data in Xianghe from November 2017 to January 2018. On this basis, a parameterized scheme suitable for reconstructing j(NO₂) in the Xianghe area was constructed. The results indicate that the variation trends of j(NO₂) and solar radiation in Xianghe are basically the same, and the diurnal variations are all unimodal with high noon and small morning and evening. The variation range of j(NO₂) in winter is 0.00046-0.0044 s^-1, with a mean of 0.0029 s^-1. Since j(NO₂) correlates well with the clear sky index (K_S) and transmittance of ultraviolet radiation (K_UV), an experimental estimating equation based on K_UV was established using the correlation between j(NO₂), air mass number, and clear air index. Considering the clear sky index K_S is more easily obtained and global radiation is a conventional observation of meteorological stations, an experimental estimating equation was established based on K_S. The instantaneous value of j(NO₂) can be estimated by the equations established using K_UV and Ks, and the mean absolute percentage errors between the instantaneous values obtained by the two equations and the observed value are 6.5% and 13.9%, and the root mean square errors are 0.00029 and 0.00051, respectively.