'99 Update

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Air Pollution

Introduction

The air contains a wide variety of substances as particles, vapours and gases. If these substances harm human health, harm the environment, or cause a nuisance, then the air can be described as being polluted.

We can look in Hertfordshire at trends in air pollution, and whether it is getting better or worse, by looking at three particular pollutants. We measure the concentration of nitrogen dioxide (NO2) at specific sites in each district or borough of the county, and record the number of days in each year when ozone pollution is classed as 'low', 'moderate', 'high' or 'very high'. Particulates (PM10) are measured at 7 sites.

Improved Air Quality Monitoring in Hertfordshire

Monitoring of the air pollution in Hertfordshire has never been so widespread or so accurate as it is today. Almost every district/borough council has at least one monitoring site that measures for air pollution continuously. These sites are often supplemented by non-continuous air pollution monitoring, such as passive diffusion tubes measuring monthly NO2 concentrations, at many sites throughout the district/borough.

Indicator 1: Nitrogen Dioxide

In towns, most nitrogen dioxide in the air will have come from road vehicles. Nitrogen dioxide is harmful in two main ways: it can cause breathing problems and it also contributes to the problem of acid rain. Acid rain is harmful to nature and it can also damage buildings by attacking the materials the building is made of.

Estimated Annual Average Nitrogen Dioxide Concentration 1998 & 1999

The results so far for 1999 indicate that for 6 out of the 10 Hertfordshire districts the concentrations of nitrogen dioxide currently exceeds the National Air Quality Strategy (NAQS) standard of 21 ppb. The current NAQS objective is to achieve a nitrogen dioxide concentration below this standard by the year 2005. In most cases the results for 1999 are higher than for 1998 due to the different weather conditions.

Indicator 2: Ozone

Ozone is called a 'secondary pollutant'. This means that ozone is not emitted directly into the atmosphere, but is formed in the air by a complex series of chemical reactions powered by sunlight, so ozone pollution is worse on sunny summer days than in the winter. This is 'ground level ozone pollution' and should not be confused with the 'hole in the ozone layer' which is high above the earth. Ozone high in the atmosphere protects us from the sun, therefore lack of ozone in the upper atmosphere also causes a problem. Ozone at ground level can irritate your eyes, nose and throat and it can cause coughs and headaches.

Ozone is now monitored continuously at six sites in Hertfordshire. Overall ozone pollution in Hertfordshire is within the 'low' or 'moderate' bands, however several days of 'high' ozone pollution have been measured so far in 1999.

Ozone Concentrations 1998 & 1999
Percentage of Days in Each DETR Air Pollution Band

Indicator 3: Particles - PM10

Particles in the atmosphere come from a wide range of sources and are made up of a wide variety of substances. They can come from road traffic, be formed by chemical reactions in the atmosphere, or may even be seasalt, biological particles or dust. Particulate air pollution is associated with a range of effects on health including effects on the respiratory and cardiovascular systems, asthma and mortality.

Particles are now monitored continuously at seven sites in Hertfordshire. Overall particulate pollution in Hertfordshire is within the 'low' band, however several days of 'moderate' particulate pollution have been measured so far in 1999.

For further information contact: Alan Gough, Watford Council, 01923 226400