Timeseries of the Antarctic ozone loss in the last 10 years, in megaton ozone
Timeseries of the Antarctic ozone loss in the last 10 years, in megaton ozone
In the analysis by the Royal Netherlands Meteorological Institute (KNMI), ozone loss on 1 October was more than the record ozone loss that was measured in the year 2000. Ozone loss is the quantity that is commonly used to quantify the amount of ozone depletion in the ozone hole. It depends on both the area and the depth of the ozone hole.

The KNMI has measured the thickness of the ozone layer with the satellite instruments GOME (since 1995), SCIAMACHY (since 2002) and OMI (since 2005). The KNMI coordinates the quality control of the SCIAMACHY instrument, and is the principle investigator of the Dutch-Finnish OMI instrument.

The ozone hole appears annually in spring (autumn in the Northern Hemisphere) over Antarctica since the 1980’s. It is caused by chemical depletion of ozone by chlorine, released from chlorine compounds like CFCs that were used until recently in aerosol sprays and refrigerators.

The fast depletion of ozone requires both very low temperatures and sunlight. These conditions are met in early spring over Antarctica. This year the temperatures in the Antarctic ozone hole are the lowest since the beginning of the satellite measurements in 1979, which explains the extreme loss of ozone this year.

Production of CFCs has been phased out since the late 1980’s and the amount CFCs in the atmosphere has been decreasing slowly in the last few years. It is expected that the ozone hole will disappear in the course of this century. However, this process is slowed down by a gradual cooling of ozone layer, as a result of the enhanced greenhouse effect. (This effect leads to higher temperatures near the earth’s surface, and to lower temperatures at the altitudes between about 10 and 25 km where the ozone layer is situated.)

Although it is expected that the ozone hole will eventually disappear, the exceptionally large ozone hole of this year shows that this process has not started yet.