Antarctic ozone hole. Satellite image of the ozone hole (blue) over Antarctica (centre) on 12th September 2010. 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 25th September 2010, covering an area of over 22 million square kilometres, the second smallest in over a decade. The amount of ozone depleting substances are decreasing 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.