Ozone depletion in the Arctic

The areas generally north of 60o and the Arctic – which is to say, a good deal of Norway – are where the largest uncertainty lies in terms of ozone depletion. There have been large year-to-year variations over the last 10 years, as shown by NILU’s measurements. According to a report from the WMO/UNEP, there has been a steady increase in observations in the last decade of the conditions that lead to ozone depletion at these latitudes (see picture of clouds).
 

Picture: Polar stratospheric clouds over Kjeller and Oslo.

The reason for this is uncertain, but it is known that ozone breakdown is very dependent on stratospheric temperatures. The colder it is, the more ozone is lost as a result of the formation of polar stratospheric clouds (PSC), or mother-of-pearl clouds.

PSCs dramatically amplify chemical ozone depletion. Sunlight initiates the formation of chlorine compounds in the stratosphere as a result of reactions that take place on the PSC particles. These chlorine compounds react further with ozone in catalytic processes, which results in severe ozone depletion. There are two main types of PSCs, PSC I and PSC II. Type I is formed when temperatures are below -78 ° C and Type II, when temperatures are below -85 C. Type II clouds are the most effective with respect to ozone degradation. The first observation of PSC II clouds in the Arctic was in the winter of 2004/2005, when the stratosphere was extremely cold. Record levels of the chemical depletion of ozone were recorded in the Arctic in 2011.