Frequently Asked Questions are shown below. If you have a question that does not appear below, please contact us at info@kentair.org.uk 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 http://uk-air.defra.gov.uk/air-pollution/daqi. 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 - ie 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 are 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: https://uk-air.defra.gov.uk/air-pollution/uk-eu-limits.

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 gravimatric and automatic monitors which have a sample inlet which is designed to collect only particles on the PM10 size fraction.

What PM2.5 is exactly and how it is measured?

PM2.5 is also known as fine particulate matter (2.5 micrometres is one 400th of a millimetre). Monitors measure the mass per cubic metre of air of particles and and liquid droplets in the air with a size (diameter) generally less than 2.5 micrometres (µm). PM2.5 is measured by a range of gravimetric and automatic monitors which have a sample inlet which is designed to collect only particles in that size fraction.

The biggest impact of particulate air pollution on public health is understood to be from long-term exposure to PM2.5 particles, which increases the age-specific mortality risk, particularly from cardiovascular causes as they can reach deep into the lungs and enter the blood stream. Children, the elderly, and those with predisposed respiratory and cardiovascular disease, are known to be more susceptible to the health impacts from this and other air pollution.

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 = 1.9957 µg m-3 1 ppb = 1.96 µg m-3
Nitrogen Dioxide 1 ppb = 1.9125 µg m-3 1 ppb = 1.88 µg m-3
Carbon Monoxide 1 ppb = 1.1642 mg m-3 1 ppb = 1.15 mg m-3
Sulphur Dioxide 1 ppb = 2.6609 µg m-3 1 ppb = 2.62 µg m-3
Benzene 1 ppb = 3.2430 µg m-3 1 ppb = 3.19 µg m-3
1,3-butadiene 1 ppb = 2.2452 µg m-3 1 ppb = 2.21 µg m-3

NOx in µgm-3 is expressed as NO2 i.e. (NO ppb + NO2 ppb) * 1.9125 = NOx µgm-3.

In the UK Indicative gravimetric equivalent PM10 data are calculated from TEOM monitoring data by applying a default factor of 1.3.

How can weather affect pollution episodes?

Ground level ozone is not emitted directly into the air but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC). This happens when pollutants emitted by cars, power plants and other sources chemically react in the presence of sunlight. Higher air temperatures can speed up chemical reactions in the air.

Rain typically results in less pollution since it washes away particulate matter.

During a heat wave, air is often stagnant with low wind movement, so polluted air is not dispersed as well as it would on a windy day.

Higher wind speeds generally create a greater dispersion of air pollutants, resulting in lower air pollution concentrations. A good brisk wind can disperse pollutants, easing air pollution. But if you are downwind of a large wildfire, wind will bring that smoke and ash to you.

Actions we can take when there is a pollution episode

Kentair - act and sign up to https://kentair.org.uk/forecast-sign-up for air pollution forecast

Drive less or use other less polluting forms of transport such as carsharing, public transport or riding a bike


– Avoid lighting a fire in unsuitable weather conditions - smoke hangs in the air on damp, still days and in the evening. If it is very windy, smoke may be blown into neighbour's gardens and across roads.

– Avoid bonfires when air pollution in your area is high or very high.

Wood burning advice

– Open fireplaces are the most polluting. The most efficient stoves produce up to 90% less pollution than an open fire and up to 80% less than a stove that is more than 10 years old. A list of the cleanest stoves can be found here.

– It’s important to make sure that wood is dry and well-seasoned (lower moisture content) to prevent nuisance smoke. Use Ready to Burn wood fuel as it has a moisture content of less than 20% and is suitable for immediate use. Storing your wood correctly can help keep it dry, make sure it does not get damp from the rain or damp in the ground.

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.