Impact of averaged photolysis rates on stratospheric chemical models

An evaluation is made of the effect of two approximations to the diurnal variation of photolysis rates on the simulation of stratospheric chemistry. The daylight average approximation uses photolysis rates that are given a value representative of the daylight average over that portion of the day that the Sun is shining, and zero otherwise. Although this distorts the diurnal cycle, the zonal average concentrations using this approximation are within about 5% of those from the fully resolved diurnal cycle for most of the important species in the stratosphere. Larger discrepancies occur in the partitioning of inorganic chlorine, although even this is in error by only 10% for the dominant species. -from Author