4. Ozone levels in the upper atmosphere of the Antarctic region on September 7, 1999, as measured by NASA's Total Ozone Mapping Spectrometer (TOMS) onboard the Earth Probe (EP) satellite. The Antarctic ozone hole is indicated by the pink, violet, purple, and dark blue regions, in contrast to the light blue, brown, yellow, and green regions farther north, which indicate higher ozone concentrations. No data exist for white regions.
(The color code in this image refers to Dobson units, which measure the concentration of ozone in the Earth's upper atmosphere. For instance, "300 Dobson units" refers to the ozone concentration averaged over the entire Earth. Dobson units of less than 300 mean a lower concentration than the average; Dobson units of more than 300 mean a higher concentration than the average.)
Image Credit: Ozone Processing Team, NASA/Goddard Space Flight Center.