THE DISTRIBUTION OF ACETALDEHYDE IN THE LOWER TROPOSPHERE DURING TROPOZ-II

A series of 72 measurements of the acetaldehyde (CH3CHO) mixing ratio were made in the lower troposphere during TROPOZ II. These measurement s are the first ever made of the background level of this trace gas in the free troposphere. The data show a vertical decrease of the CH3CHO mixing ratio with increasing altitude and indicate higher CH3CHO conc entrations in the Northern Hemisphere - in general agreement with a mo del-derived average CH3CHO distribution. Deviations of the observed CH 3CHO mixing ratios from the modelled mean distribution are correlated with similar deviations in the corresponding HCHO mixing ratios.