Air Quality & Noise Monitoring Program


Frequently Asked Questions are shown below. If you have a question that does not appear below, please contact us at and we will respond to your query.

What are the effects of air quality?
Impacts of Air Pollution can be both natural and man-made and have an impact both indoors and outside. Although natural emissions of air pollution may impact upon the environment from time to time, for example through a volcanic eruption, it is most often man-made air pollution which can lead to poor air quality on a more regular basis.

Outdoors, common air pollutants which affect ambient air quality include sulphur dioxide, nitrogen oxides, carbon monoxide, particulate matter and volatile organic compounds (VOCs), emitted through the burning of fossil fuels for energy and transportation.

Ozone, a secondary pollutant, is formed in the atmosphere near ground level when primary pollutants are oxidised in the presence of sunlight. The resulting cocktail of pollution can have detrimental effects on human health, wildlife and vegetation.

Asthma is an increasingly common respiratory disease which may be triggered by air pollution. In addition, sulphur dioxide and nitrogen oxides may be converted into acids, and deposited as acid rain.

Indoors, poor ventilation can lead to a build-up of air pollutants, including carbon monoxide and nitrogen dioxide from faulty gas heaters and cookers, carbon monoxide and benzene from cigarette smoke, and volatile organic compounds (VOCs) from synthetic furnishings, vinyl flooring and paints.

Like outdoor pollutants, indoor pollutants may also act as triggers for attacks of asthma. Since most of us spend up to 90% of the time indoors, indoor air quality could have a real bearing on our health.

How can "air quality" be defined?
Air quality refers to the degree of pollution in the atmosphere and is using an index system which is described on page Air pollution is the contamination of the air by noxious gases and minute particles of solid and liquid matter (particulates) in concentrations that endanger health. The major sources of air pollution are transportation engines, power and heat generation, industrial processes, and the burning of solid waste.

Where are the lowest air pollution areas? As a generalisation, how do urban, rural & coastal areas compare?
There is no simple answer to this frequently asked question. Pollution builds up in towns and cities where it can become trapped between buildings, and in prolonged still, sunny weather in the summer and in still foggy weather in winter.

It will also build up in low lying areas - i.e. valleys, between hills etc. - so pollutant levels are dependent on topography of the area and weather conditions, as well as local and regional sources. Pollutants may also be carried long distances on prevailing winds. For example, polluted air masses from Europe sometimes contribute to high ozone levels on the south coast.

Ozone levels are often higher in the countryside than towns, but the pollutants that form it are generally generated in towns. Generally, open areas and coastal areas should be cleaner as air changes more frequently (apart from seaside resorts on a hot bank holiday!).

What is the safe levels of pollutants?
The government has set standards for levels of air pollution which should not be exceeded to protect human health. These can be found at:

What are the main sources of air pollution?
Air pollutants occur both outdoors or indoors, and can be natural or man-made. Outdoor air pollution, sometimes called ambient air pollution, occurs in both urban and rural areas, although a different mix of air pollutants may be found in the countryside to that found in a city. Typical urban air pollutants from man-made activities include nitrogen oxides, carbon monoxide, sulphur dioxide, hydrocarbons and particulate matter. All these pollutants are called primary pollutants because they are emitted directly into the atmosphere.

Common sources of these primary pollutants include power station and industrial plants (sulphur dioxide), and road transport (carbon monoxide, particulate matter and nitrogen oxides). Ozone is a secondary pollutant, formed in the air as a result of chemical reactions.

What PM10 is exactly and how it is measured?
PM10 particulates are small particles with an aerodynamic diameter less than or equal to a nominal 10 microns (1 micron = 1 millionth of a metre). Their small size allows them to make their way to the air sacs deep within the lungs where they may be deposited and result in adverse health effects. PM10 is measured by a range of gravimetric and automatic monitors which have a sample inlet which is designed to collect only particles on the PM10 size fraction.

For Gaseous Pollutants, what are the conversion Factors between ppb and µg m-3 and ppm and mgm-3?
For the Kent and Medway region the appropriate conversion factors at 20°C and 1013 mb are used.
Pollutant EC
20°C and 1013mb
25°C and 1013mb
Ozone 1 ppb = 2.00 µg m-3 1 ppb = 1.96 µg m-3
Nitrogen Dioxide 1 ppb = 1.91 µg m-3 1 ppb = 1.88 µg m-3
Carbon Monoxide 1 ppb = 1.16 mg m-3 1 ppb = 1.15 mg m-3
Sulphur Dioxide 1 ppb = 2.66 µg m-3 1 ppb = 1.15 µg m-3
Benzene 1 ppb = 3.25 µg m-3 1 ppb = 3.19 µg m-3
1,3-butadiene 1 ppb = 2.25 µg m-3 1 ppb = 2.21 µg m-3

NOx in µgm-3 is expressed as NO2 i.e. (NO ppb + NO2 ppb) * 1.91 = NOx µgm-3.

Get more information

For more information about air quality and how it affects the UK, visit the UK-AIR Air Quality website from Defra to find out more.