The latitudinal distribution (50°N–50°S) of NO2 and O3 in October/November 1990

Abstract

The present paper reports on shipboard DOAS (Differential Optical Absorption Spectroscopy) measurements of stratospheric NO2 and O3 vertical column abundances. The data were obtained between 50°N and 50°S during October and November 1990, before the eruption of Mt. Pinatubo. The daily measurements were made during morning and evening twilight. The retrieved column abundances were averaged over a solar zenith angle (SZA) range of 87° to 91°, for both NO2 measured in the visible wavelength region and for O3 measured in the UV. The instrumentation and the data evaluation technique are briefly discussed.In the Northern Hemisphere (autumn) the NO2 vertical column abundances show a steady decrease from 50°N to the equator, while in the Southern Hemisphere (spring) the corresponding increase with latitude is both more pronounced and more variable. Depending on latitude, the measured mean am/pm ratios are between 0.55 and 0.63, generally consistent with the pre‐Pinatubo overnight conversion of NO2 to N2O5.Within the estimated error of our DOAS measurements, the retrieved O3 vertical column amounts are in good agreement with the TOMS data. Both data sets show a slightly different longitudinal distribution than expected from the O3 climatology.