LATITUDINAL VARIATION OF MEASURED NO2 PHOTOLYSIS FREQUENCIES OVER THE ATLANTIC-OCEAN BETWEEN 50-DEGREES-N AND 30-DEGREES-S

Using a filter radiometer, the meridional profile of the NO2 photolysis frequency, J(NO2), was measured between 50-degrees-N and 30-degrees-S during the cruise ANTVII/1 September/October 1988 of the research vessel Polarstern on the Atlantic Ocean. Simultaneously, global broadband irradiance and aerosol were monitored. Clean marine background air with low aerosol loads (b(sp) = (1-2) x 10(5) m-1) was encountered at the latitudes 25-degrees-N-30-degrees-N and 18-degrees-S-27-degrees-S, respectively. Under these conditions and an almost cloudless sky J(NO2) reached 7.3 x 10(-3) s-1 (2pi sr) for a zenith angle of 30-degrees. Between 30-degrees-N and 30-degrees-S, the latitudinal variation of the J(NO2) noontime maxima was less than +/- 10%, while the mean value at noon vas 7.8 x 10(-3) s-1. For the set of all data between 50-degrees-N and 30-degrees-S, a nearly linear correlation of J(NO2) vs. global broadland irradiance was found. The slope of (8.24 +/- 0.03) x 10(-5) s-1/mW cm-2 agrees within 10% with observations in Julich (51-degrees-N, 6.2-degrees-E).