Most ozone is found in the stratosphere, with peak values in number density of 5 x 1012 molecules/m3 around 22 km and a peak value in mixing ratio of 8-10 ppmv around 35 km. In addition to the difference in appearance of the ozone profile due to the units in which it's measured, the shape and the peak altitude of the profile vary with latitude and season. The shape of the profile can also vary due to dynamical or chemical processes, the most notable example being profiles taken in the Antarctic ozone hole, where large chunks of the ozone profile have been lost due to chemical processes, occurring in the context of special meteorological processes.
Below the ozone peak, ozone molecules have long lifetimes and therefore behave essentially as a tracer of atmospheric motion. Above the ozone peak, ozone is photochemically controlled, with rapid creation and destruction of ozone molecules leading to a short lifetime. Dynamical features evident in ozone fields at low altitudes where ozone lifetimes are long do not appear at high altitudes where ozone is photochemically controlled.
TOMS measurements show that a typical column of ozone contains about 300 DU. Measurements vary significantly with latitude and season. The largest values of ozone are typically found at high northern latitudes during the northern winter, and mid- to high southern latitudes during the Austral (southern) winter. Low values and little interseasonal variability characterize ozone column amounts in the tropics. Very low values (as low as 110 DU) are seen in the Antarctic regions during the Austral spring when the ozone hole is present.
Time series of the TOMS data have shown that ozone in Antarctica during the Austral spring has steadily decreased since 1978. In fact, there did not appear to be an ozone hole in the TOMS data in the late 1970s. Recent ozone measurements in the Antarctic ozone hole have fallen to near 110 DU.
We also know from Dobson's data that no ozone hole existed back in the late 1950s. While Dobson showed that the annual cycle of ozone over Antarctica was quite different from what had been seen in the Arctic latitudes of the northern hemisphere, Dobson's measurements were some 180 DU higher than what TOMS reports today.
By examining the zonal mean TOMS data, we have been able to observe and characterize the annual variability of ozone. Long time series records of averaged TOMS data showed a clear annual cycle, but also year-to-year variability and some higher order variability as well. Data from the northern mid latitudes showed larger annual variability, but less high order variability. The Fresno data set indicated that ozone can vary by as much as 25 percent from one day to the next. Typical variability, however, is on the order of 5 percent or less.