Estimations of Photolysis Frequencies of Ozone and Nitrogen Dioxide Using Satellite Data over East Asia

Solar ultraviolet (UV) radiation plays an important role in atmospheric photochemistry. UV radiation dissociates molecules (e.g., ozone; O₃ and nitrogen dioxide; NO₂) into the photolysis of species in the troposphere. The photolysis frequencies of O₃ and NO₂ are related to air pollution in the urban environment. The photolysis of O₃ is associated with the formation of hydroxyl radical (OH) that plays an essential role in secondary newly particle formation. On the other hand, the photolysis of NO₂ formed surface ozone.

In this study, we evaluate the photolysis frequencies of O₃ and NO₂ using OMI and TROPOMI satellite over East Asia. The actinic flux is simulated using a radiative transfer model, linearized pseudo-spherical vector discrete ordinate radiative transfer (VLIDORT). Then the photolysis frequencies are calculated using the actinic flux, absorption cross-section, and photolysis quantum yield. The cloud effect (cloud optical depth; COD) is estimated using the satellite reflectance based on the look-up table approach. The photolysis frequencies attenuated when clouds are present, and the amplitude of this attenuation increases with increasing COD.