Parametrization of NO2 photodissociation rate

31-12-1995 | Publication

The NO2 photodissociation rate, j(NO2), plays a key role in atmospheric chemistry. It is one of the most sensitive parameters in atmospheric photochemical transport models. In transport models estimates of the photolysis rates are generally based on radiation transfer (sub-) models or on empirical relations.

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).