Overview of air pollutants 

You can select information about the air pollutants below. Each description page will allow you to find out more about the pollutant itself, related issues and a timeseries graph.

Air pollutants

Heavy metals and base cations


Emissions of air quality pollutants in the UK contribute to both local and transboundary air pollution. The NAEI calculates and reports on the quantity of pollutants that are emitted to air. This impacts on the concentrations of pollution in the air, although there is not a direct relationship between the two as concentrations can be affected by weather patterns, chemical transformations, and pollutants emitted elsewhere.

'Transboundary air pollution' refers to pollution transported in the atmosphere from one country or region to another and often undergoing chemical transformation in the process. As a result of the distances travelled and chemical changes that occur, it is very difficult to pinpoint which emission source (e.g. sulphur dioxide emissions from a factory), in which location, has led to a specific impact in another location (e.g. increased acidity in a lake).

Acidification, eutrophication and ground level ozone are effects of transboundary air pollution, arising from the emissions of the following air quality pollutants:

  • Nitrogen oxides
  • Sulphur dioxide
  • Hydrogen chloride
  • Non-methane volatile organic compounds
  • Ammonia
  • Hydrogen fluoride

Concerns about acidifying pollutants arise as when acidifying species settle and accumulate they can have adverse effects on buildings and vegetation, as well as acidifying streams and lakes and damaging the aquatic environment. Eutrophying pollutants enrich soils or rivers and lakes through rain with higher levels of nitrogen, thereby disturbing the natural balance of nutrient levels and diversity of species in sensitive environments. Ground level ozone precursors play a key role in ozone formation and ozone can affect human health and damage plants and crops.

Particulate matter (PM) is also formed from the long-range transport of precursor gases forming PM through atmospheric processes.

Local air quality can also be affected by emissions of air pollutants. High concentrations of air pollutants are known to be harmful to human health and the environment. In addition to the pollutants which affect transboundary pollution, the NAEI also reports on emissions of pollutants for which the concentrations are subject to air quality objectives and controls under the Air Quality Standards Regulations (2010)

  • The Air Quality Standards Regulations 2010 in England (UK Government , 2010), and their December 2016 amendment (UK Government , 2016)
  • The Air Quality Standards (Scotland) Regulations 2010 in Scotland (Scottish Government, 2010), and their December 2016 amendment (Scottish Government, 2016)
  • The Air Quality Standards (Wales) Regulations 2010 in Wales (Welsh Government, 2010)
  • The Air Quality Standards Regulations (Northern Ireland) 2010 (Department of Environment Northern Ireland, 2010) and their December 2016 amendment (DAERA, 2017)

These pollutants are:

  • Sulphur dioxide
  • Nitrogen dioxide and oxides of nitrogen
  • Particulate Matter
  • Lead
  • Benzene
  • Carbon monoxide
  • Ozone
  • Arsenic
  • Cadmium
  • Nickel
  • Mercury
  • Benzo(a)pyrene (BAP) and Polycyclic Aromatic Hydrocarbons (PAHs)

Important sources and trends

Sources which account for high shares of emissions differ from pollutant to pollutant. However, in general terms the combustion of solid and liquid fuels (coal, wood, oil) tend to produce the highest emissions per unit of fuel burned as well as specific industrial processes for specific pollutants. Agriculture is the dominant source of ammonia emissions.  Over the years, emissions from solid fuel combustion have declined significantly, e.g. emissions from coal combustion in the residential sector. In contrast the strong increase in the use of transportation and road traffic, an important source for many air quality and transboundary pollutants, has resulted in the increase in emissions from the combustion of petrol and diesel, although this has been counteracted by improvements in emissions from individual vehicles due to tighter vehicle emission regulations.

Emissions from all pollutants have decreased since the earliest year the data is available from (1970, 1980, 1990 and 2000, depending on pollutant) partly as a result of policies put in place to control certain emissions and a decline in the use of solid and liquid fuels in the domestic and power generation sectors. Emission trends of selected pollutants (NOx, SO2, NMVOC, NH3, PM10, and CO) from key source categories since 1990 are summarised in the latest UK Informative Inventory Report in the Reports section and Defra statistical releases.

Further information and analysis on the emission trends of all pollutants reported under the CLRTAP and NECR are available in the latest Informative Inventory Report also found in the Report section.


The UK is committed to reducing transboundary air pollution through emission targets set under the UNECE's Convention on Long-Range Transboundary Air Pollution (CLRTAP) and the National Emissions Ceilings Regulations (NECR).

Page last modified: 02 August 2022