Antarctic ozone hole. Satellite image of the ozone hole (blue) over Antarctica (centre) on 10th September 2009. 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 17th September 2009, covering an area of over 24 million square kilometres. This was the tenth 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.