THE LATITUDINAL DISTRIBUTION (50-DEGREES-N-50-DEGREES-S) OF NO2 AND O-3 IN OCTOBER NOVEMBER 1990

The present paper reports on shipboard DOAS (Differential Optical Abso rption Spectroscopy) measurements of stratospheric NO2 and 0(3) vertic al column abundances. The data were obtained between 50 degrees N and 50 degrees S during October and November 1990, before the eruption of Mt. Pinatubo. The daily measurements were made during morning and even ing twilight. The retrieved column abundances were averaged over a sol ar zenith angle (SZA) range of 87 degrees to 91 degrees, for both NO2 measured in the visible wavelength region and for 0(3) measured in the UV. The instrumentation and the data evaluation technique are briefly discussed. In the Northern Hemisphere (autumn) the NO2 vertical colum n abundances show a steady decrease from 50 degrees N to the equator, while in the Southern Hemisphere (spring) the corresponding increase w ith latitude is both more pronounced and more variable. Depending on l atitude, the measured mean am/pm ratios are between 0.55 and 0.63, gen erally consistent with the pre-Pinatubo overnight conversion of NO2 to N2O5. Within the estimated error of our DOAS measurements, the retrie ved 0(3) vertical column amounts are in good agreement with the TOMS d ata. Both data sets show a slightly different longitudinal distributio n than expected from the 0(3) climatology.