Estimating the global ozone characteristics during the last 30 years

All available total ozone data from over 150 past and present Global Ozone Observing System (GO 3 OS) stations, after careful quality control and reevaluation, have been analyzed in order to deduce the basic global ozone characteristics both for pre‐ozone‐hole and during “ozone hole” time periods. Utilizing Total Ozone Mapping Spectrometer (TOMS) data, the longitudinal inhomogeneity of the total ozone distribution was estimated. That permitted the use of ground‐based data for establishing long‐term zonal as well as hemispheric and global ozone variations for the 1964–1994 period. The difference between the estimations of monthly zonal variations from ground‐based and TOMS data for the overlapping period of 1979–1993 is less than 1% in latitudes 40°S–60°N. The ozone changes are several times larger than possible errors of the estimated values; therefore the results are highly reliable. They show that the northern hemisphere average ozone was ∼312 and the southern average was ∼300 matm cm in the pre‐ozone‐hole decades (1964–1980) and that the global average for the 1984–1993 period was lower by ∼3% (from 306.4±1.0 down to 297.7±2.2 matm cm). The southern hemisphere contributed ∼64% of the overall ozone decline. The levels of annual ozone maximum have been reduced by 5.8% in the southern hemisphere and 3.2% in the northern hemisphere, and the levels of ozone minimum have been reduced by 2.1% and 1.2%, respectively. The ozone trends for midlatitudinal bands (35–65°) show a pronounced seasonal dependence varying from ∼3% to 8 % (and even more for the southern hemisphere) for the cumulative decline since 1970. The ozone decline calculated in percent per decade from 1980 is almost twice as large as the decline calculated from 1970. The cumulative year‐round global ozone decline is 4.8±0.6%; however, the cumulative year‐round decline over middle and polar latitudes is more than 7%. The advantages of establishing ozone “norms” for estimations of long‐term ozone variations from ground‐based data are emphasized.