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Trends - Air Quality Indicators

Maps of Air Quality

Overall pollution levels in Wales have changed over the last 20 years. To an extent, these analyses are affected by changes in monitoring site numbers. Since these were relatively low up to 1999, trends in the earlier years should be regarded with caution.

In 1999, a first air quality 'headline' indicator was introduced in support of the UK Sustainable Development Strategy. In 2005, a new indicator was added, better reflecting the effects on health of long-term exposure to lower levels of pollution.

Data from the air quality monitoring networks in Wales have been combined with pollutant emissions data from the UKs National Atmospheric Emissions Inventory (NAEI) to produce detailed maps (at 1km resolution) of average or peak pollutant concentrations across the country. These maps shown below calibrated and validated against UK and Welsh monitoring data- provide a powerful tool for identifying pollutant 'hot-spots' and managing air quality problems in the most direct and cost-efficient manner.

Levels of primary pollutants, those emitted directly into the atmosphere, tend to be highest around their sources; these are usually located in urban and industrial areas. Motor vehicles are a major source of primary pollution throughout the UK. In particular, traffic is an important source of carbon monoxide, nitrogen dioxide and volatile hydrocarbons (VOCs) such as benzene and 1,3-butadiene and primary particles (PM10). Concentrations of all these pollutants are therefore usually highest in built-up urban areas.

This pattern is readily apparent from the maps below; it shows levels of traffic and industrial pollutants such as nitrogen dioxide and PM10 particles higher in the built-up parts of the country.

In general, patterns of secondary pollutants such as ground-level ozone and secondary PM10, which are formed by chemical reaction in the atmosphere, are markedly different from those of primary pollutants; they are characteristically less dependent on emission patterns, and tend to be more strongly influenced by meteorology and atmospheric chemistry. As a result, they also change more from year to year than those of primary pollutants.

The patterns of ozone concentration shown on the maps are therefore highly complex, showing some topographic-dependence; they are also considerably higher than the corresponding 2005 levels. This is due to the ozone episodes associated with the heat waves in June and July 2006. In general, ozone concentrations tend to be lower in the parts of Wales where NO2 and PM10 are higher. The south to north gradient in PM10 concentration is due to a combination of the patterns in the concentration of secondary particles and sea salt particles.

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Map showing Annual Means