Column Ozone Measurements: 1981-2011
Column ozone concentrations over Lerwick (Dobson units)
The stratospheric ozone layer, located around 10-30 km above the Earth's surface, forms a protective shield against harmful solar (UVB) radiation. Thinning of the ozone layer has occurred since the beginning of the 1980s in all regions except equatorial ones. Depletion is most marked in the Antarctic where, in 2006, the Antarctic ozone hole reached 29.5 million square kilometres in area (over 300 times the land area of Scotland).
The 1987 Montreal Protocol set guidelines to eliminate the global production and use of ozone depleting substances. European production of CFCs for non-essential use fell to zero in 1995. However, leaks form old equipment and the long life of these substances mean that full recovery of the ozone layer is not predicted until about 2050.
The total ozone levels at Lerwick vary seasonally, with maximum levels generally occurring in early spring and minimum levels in autumn. Over the last 30 years, the annual average total ozone cover over Lerwick has shown the natural interannual variability which would be expected due to varying meteorological conditions. Generally, levels have decreased over this period. More recently, it appears that this trend may be levelling out, but it is too soon to be sure.
Email: Sandy McPhee
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