Antarctic ozone hole maximum. Satellite image of the maximum extent in 2015 of the ozone hole (blue) over Antarctica (centre). Ozone layer thicknesses are colour coded from purple (lowest) through blue, cyan and green to yellow (highest). The ozone hole reached its annual maximum on 2 October 2015, covering an area of over 28 million square kilometres. This was the fourth largest ozone hole on record, though the amount of ozone depleting substances have decreased from peak levels in 2000. NASA has been monitoring the status of the ozone layer through satellite observations since the 1970s. Image data obtained by the Ozone Monitoring Instrument on NASA's Aura satellite.