The global distribution of ozone destruction rates obtained from 13 years of Nimbus/TOMS data (1979-1991)

Long-term ozone trends (percentage change) have been computed from 13 years of Nimbus/TOMS (Total Ozone Mapping Spectrometer) data as a function of latitude, longitude, and month for the period January 1, 1979 to December 31, 1991. In both hemispheres, the ozone column content has decreased at latitudes above 30 deg by amounts that are larger than predicted by homogeneous chemistry models for the 13-year time period. The largest rates of ozone decrease occur in the Southern Hemisphere during winter and spring, with recovery during the summer and autumn. The large winter ozone loss rates are consistent with observed low stratospheric temperatures, ice-cloud formation, and heterogeneous chemistry at middle and high latitudes. There are similar, but smaller changes observed in the Northern Hemisphere. At midlatitudes, (40 deg N to 50 deg N) there are increased zonal average ozone depletion rates that correspond to 5 geographically localized regions of increased ozone depletion rates. Only the equatorial band between plus or minus 20 deg shows little or no long-term ozone change since January, 1979. The long-term winter ozone depletion rate data for both hemispheres suggests that heterogeneous chemistry processes may operate over a wide range of latitudes during half of the year.