Air Quality
The air contains a wide variety of particles, vapours and gases, some natural, some man-made. Those that are considered harmful to human health, harmful to the environment, or a potential nuisance are called 'pollutants'. The Government, with advice from health experts, has set limits for each of these pollutants to help inform the public about air pollution levels.
Indicator AQ1 - Air Pollution
Indicator AQ1 (formerly QoL27) is used to illustrate air pollution levels in Hertfordshire, and show whether air quality is getting better or worse. The indicator is calculated using accurate measurements collected continuously from a number of monitoring sites around the county and has five separate values;
- the number of days in which ozone levels in rural areas exceeded the Government's standard;
- the number of days in which particulate levels in urban areas exceeded the Government's standard;
- the number of days in which particulate levels close to busy roads exceeded the Government's standard;
- annual mean nitrogen dioxide levels in urban areas and
- annual mean nitrogen dioxide levels close to busy roads.
Not all districts and boroughs in Hertfordshire have the facility to calculate these indicators. Therefore, one overall set of indicator values has been calculated for the whole of the county. Where possible, results from a number of districts are used to produce an average.
The two graphs show how the five air pollution indicators have changed for Hertfordshire since 2000. Local pollution levels are dependent on a range of factors including traffic levels, vehicle technology, imported pollution from other areas such as London and continental Europe, and the weather. It usually takes a long time for emissions from traffic and other sources of pollution to change, so short-term variations in the indicator are largely due to weather conditions. The ozone is formed in the atmosphere by a chemical reaction in the presence of sunlight. As a result; a warm sunny summer will cause the rural ozone indicator to go up. A cold, still winter will cause the urban and roadside indicators to go up.
All of the indicators for 2004 were lower than 2003. Unlike 2003, there were no exceptionally extended pollution episodes during 2004 due to the more unstable weather conditions experienced. There were no incidences of 'moderate' carbon monoxide or nitrogen dioxide recorded by any network site during the year. There were a number of days where 'moderate ozone' was recorded across the network, the earliest of these widespread incidents occurred during mid-March, the last at the beginning of September. There were very few incidents of 'high' ozone recorded with only the Hertsmere rural site recording more than a single day.
Annual means for Nitrogen Dioxide
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No. of days levels exceeded government targets
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Local authorities in Hertfordshire are required to make regular detailed studies of air pollution levels throughout their areas. Where they estimate that air quality will not meet the Government's standards by specified dates, they have to produce action plans describing how they intend improving the situation. Air quality monitoring in Hertfordshire is coordinated through the Hertfordshire and Bedfordshire Air Pollution Monitoring Network. More detail on the monitoring network including measurements, reports and daily bulletins can be found through the Network's website: www.hertsbedsair.org.uk.