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Trends - Air Quality Indicators

Ozone and PM10 Particulate Matter Trends

The graph below shows how annual mean concentrations of PM10 and ozone in Wales have changed in recent years.

Click on the image below to open a larger version in a new window.

Graph showing Ozone and PM<sub>10</sub> Particulate Matter Trends

In rural areas (where highest concentrations of ozone tend to occur) there appears to be no clear trend in average concentrations of this pollutant. In urban areas, background concentrations appear to have increased during 1993 to 2003, before subsequently levelling off (although this trend should be interpreted with caution, as prior to 2002 it is based on less than four monitoring sites). Concentrations of ozone fluctuate considerably from year to year because of variations in meteorological factors.

By contrast, average concentrations of PM10 particulate at both traffic urban (sites within 10 m of the kerb of an urban road) and background urban (sites within urban areas but not close to major roads) appear to show a general downward trend over the past decade. Again, prior to 2002 the trend should be treated with caution as it is based on a small number of monitoring sites.