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What causes Air Pollution?

Air pollution was originally considered as a problem mainly associated with domestic heating and industrial emissions, which are now controllable to a great extent. Despite significant improvements in fuel and engine technology, our environment is mostly dominated by traffic emissions.

The combustion of fuels, either for engines, heating or other processes cause emissions to the air. Pollutants are either directly emitted or in reaction with other pollutants or the atmosphere can create higher concentrations of a pollutant. Emissions of harmful pollutants has greatly reduced due to cleaner fuels, such as lead-free petrol, controlled clean-up technology, such as in industrial chimney scrubbing systems or particulate traps in diesel vehicles, more pollution control regulation and cleaner alternative technology, such as more efficient engines.

Motor vehicles are the main source of air pollution in Sussex, with the high volumes of vehicles on the road and congested traffic causing a large proportion of the emissions. Emissions from domestic, commercial and industrial premises contribute to the emissions of pollutants to air as well as shipping, agriculture, landfills and air craft. As a result, the air we breathe can contain a cocktail of various pollutants. Locally the main concerns are about air pollution are from nitrogen dioxide (NO2), particulates (PM10) and ozone (O3).

Sources of pollutants

The main sources of nitrogen dioxide (NO2), are from traffic and other combustion processes such as the electricity supply industry.

The main sources of particulates (PM10) are traffic, power stations, re-suspended dusts, trans-boundary (long range transported) dust, sea salt, biomass and shipping in the future.

The main sources of ozone (O3) are emissions from other gaseous pollutants* such as nitrogen oxides (NOx), nitrogen dioxide (NO2) and Volatile Organic Compounds (VOC’s) (both man made and naturally occurring). The sources of VOCs are similar to those described for NO2 above, but also include other activities such as solvent use, and petrol distribution and handling.

*Ozone is not emitted directly from any man-made source in any significant quantities. In the lower atmosphere, O3 is primarily formed by a complicated series of chemical reactions initiated by sunlight. These reactions can be summarised as the sunlight-initiated oxidation of volatile organic compounds (VOC’s) in the presence of nitrogen oxides (NOx).

Levels of air pollution can be influenced by:

  • distance from the source of pollution
  • local landscape features and surroundings
  • local and regional sources of pollution
  • seasonal variations and prevailing conditions

Air Pollution Episodes

Air pollution episodes are generally associated with low wind conditions. Episodes can occur in different seasons and in Sussex we tend to have summer time ozone episodes and some wintertime particulate episodes.

Ozone episodes usually occur on hot, sunny and relatively still summer days, called summer smogs. Ozone levels in Sussex are amongst the highest recorded in the UK, because of the relatively sunny and warm weather conditions prevailing in the region. Emissions from continental Europe are also thought to contribute to the relatively high ozone levels observed in our region. In Sussex, health standards are usually exceeded for ozone on 30-40 days in summer each year.

Summer Smog

(Images courtesy of the Department for Environment, Food and Rural Affairs)

Wintertime episodes (smogs) occur in cold, windless conditions, called inversions. Pollutants gets trapped within the inversion ("lid" of cold air) and do not disperse (mix and disappear), this causes pollutants to remain in the vicinity and build up. These episodes tend to occur for short periods (1-2 days) and are less frequent than summer-time episodes, occurring approx. less than 3- 4 times per year.

Winter Smog

(Images courtesy of the Department for Environment, Food and Rural Affairs)

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