Ground Level Ozone Concentrations: 1990-2011
Number of days exceeding 100µg/m3 (maximum 8hr running mean)
Ozone in the stratosphere forms a layer that protects the earth against harmful ultra-violet radiation, but tropospheric (ground level) ozone is a damaging oxidant. Exposure to high ozone concentrations can cause respiratory damage, and affects vegetation by damaging leaves and reducing yields.
Ozone is formed by a slow, complicated series of reactions from other pollutants that may be blown over from Europe. The most important man-made precursors are nitrogen oxides and volatile organic compounds produced by road transport, industrial processes and solvent use. Ozone concentrations tend to be lower in urban areas where it is converted to nitrogen dioxide by reacting with nitrogen oxides.
The Air Quality Strategy objective for ground level ozone concentration (to be met by 2005) states that the maximum daily concentration (measured as an 8-hour running mean) of 100µg/m3 should not be exceeded more than 10 days per year. In 2011, this objective was met at 8 of the 11 sites. The sites that failed were Straith Vaich, Bush Estate and Lerwick. Since 1990 there has been relatively little variation in annual average concentrations.
Email: Sandy McPhee
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