Parametrization of NO2 photodissociation rate

The theoretical determination of j(NO₂) is in general too complex for implementation in atmospheric transport models. For application in transport models it is convenient to have a simple, analytical expression that adequately relates j(NO2) to routinely available meteorological parameters (global radiation, cloud cover, zenith angle). In this report j(NO₂) - estimated from hourly measured concentrations of NO, NO₂ and O₃ - is related to the measured global radiation and to the solar zenith angle. The derived empirical relations show a good agreement between observed and calculated values with an estimated relative error of ca 25%. For partly clouded skies (cloud covers N < 0.5) the attenuation of j(NO₂) is small ; for overcast situations j(NO₂) is reduced to ca. 50% of its clear sky value. Cloud cover more strongly attenuates global radiation than j(NO₂).