A new determination of extinction due to atmospheric aerosols and the resulting implications for upper stratospheric ozone depletion

A crucial question in the statistical analysis of measurements of the vertical distribution of atmospheric ozone centers on the essential aerosol corrections to these data. A lack of global coverage of the atmospheric aerosol content leads to possible biases in these corrections. Limited aerosol data are available for correcting these ozone measurements and are in the form of broad-band transmission data from a single station. The effective wavelength of these transmission data is 7350 Angstroms which is far removed from the 3200 Angstrom wavelength of the ozone measurements. With the added uncertainty of the injection altitude of volcanic aerosols, these weaknesses point out the need for a better understanding of the spatial and temporal trends in atmospheric aerosols.;To resolve these weaknesses, atmospheric extinction coefficients, which were obtained from astronomical photometric observations, have been compiled, standardized, and analyzed. These extinction coefficients provided a means of extracting the extinction and transmission due specifically to atmospheric aerosols. These aerosol transmissions were analyzed for trends, and the wavelength dependence of the aerosol extinction coefficients was characterized to provide the necessary input for corrections to the measurements of atmospheric ozone.;Three primary weaknesses of the aerosol corrections to the ozone measurements have been effectively addressed by this research. The spatial, temporal, and wavelength dependencies of the atmospheric aerosol transmission which were found in the course of this research resulted in significant changes in the trend estimates for ozone. In particular, the trend estimates for depletion of upper stratospheric ozone were reduced from 0.08% to 0.05% per year for the 1970 to 1980 decade. These new data suggest that the original trend estimates were probably influenced by long-term and possible cyclic trends of aerosol transmission.