Model-aided radiometric determination of photolysis frequencies in a sunlit atmosphere simulation chamber

[摘要] In this work diurnal and seasonal variations of mean photolysisfrequencies for the atmosphere simulation chamber SAPHIR atForschungszentrum Jülich are calculated. SAPHIR has a complexconstruction with UV permeable teflon walls allowing naturalsunlight to enter the reactor volume. The calculations are basedon external measurements of solar spectral actinic flux and amodel considering the time-dependent impact of shadows fromconstruction elements as well as the influence of the teflonwalls. Overcast and clear-sky conditions are treated in aconsistent way and different assumptions concerning diffuse skyradiance distributions are tested. Radiometric measurements insidethe chamber are used for an inspection of model predictions. Underovercast conditions we obtain fractions of 0.74 and 0.67 ofexternal values for photolysis frequencies j(NO₂) (NO₂+hν→NO+O(³P)) and j(O¹D)(O₃+hν→O₂+O(¹D)), respectively. On a clearsky summer day these values are time-dependent within ranges0.65-0.86 and 0.60-0.73, for j(NO₂) and j(O¹D),respectively. A succeeding paper (Bohnet al., 2004) is dealing withan on-road test of the model approach by comparison withphotolysis frequencies from chemical actinometry experimentswithin SAPHIR.

[学科分类] 大气科学