Air quality

Air pollution occurs when quantities of substances which have harmful effects are released into the atmosphere. Harm includes both acute and chronic effects on human health, affecting several different systems and organs, and environmental damage. Some form of air pollution control has existed as far back as the thirteenth century. Legislation imposes controls on emissions from all areas of businesses and private persons to prevent air pollution; industry and transport are particularly affected.


Air quality legislation is largely organised around the restriction of emissions to the air of specific substances found to be harmful to the environment and to human health.

Common pollutants


Industry sources: Arises mainly from combustion of petrol. Main sources are motor vehicles and other machinery, with other sources processes like synthetic rubber production for tyres.

Ammonia (NH3)

Industry sources: Mainly from agriculture, primarily livestock manure/slurry management and fertilisers, and, to a lesser extent, other sources like transport and waste disposal.

Benzene (C6H6)

Industry sources: Primarily domestic and industrial combustion, including industrial solvents, and road transport.

Carbon monoxide (CO)

Industry sources: Incomplete combustion of carbon containing fuels, mainly from road transport, as well as residential and industrial combustion.

Ground-level ozone (O3) – arises from chemical reactions between various air pollutions, primarily NOx and volatile organic compounds (VOCs), initiated by strong sunlight.

Lead (Pb) and heavy metals

Industry sources: Combustion processes, including industrial activities, traffic, energy production, iron, steel and non-ferrous metals processes and the incineration of metal-containing waste, particularly batteries and electronic equipment.

Nitrogen oxides (NOX)

Industry sources: All combustion processes in air; mainly from road transport, electricity supply, other industrial and commercial sectors, and livestock farming.

Particulate Matter (PM-10 and 2.5) microscopic particles of matter suspended in the air, from both natural and anthropogenic sources

Industry sources: Stationary fuel combustion, transport (engine emissions, tyre and brake wear and other non-exhaust emissions), quarrying, construction, and non-road mobile sources.

Polycyclic aromatic hydrocarbons (PAHs)

Industry sources: Domestic coal and wood burning, fires (accidental fires, bonfires, forest fires, etc), and industrial processes such as coke production. Road transport is the largest source for total PAHs, although it is dominated by types thought to be less hazardous.

Sulphur dioxide (SO2)

Industry sources: Combustion of sulphur-containing fuels, such as coal and heavy oils by power stations and refineries, and metal smelting processes. In some parts of the UK, notably Northern Ireland, coal for domestic use is a significant source.

Anthropogenic sources

Stationary point sources: A single, identifiable source, eg. combustion furnace flue gas stack.

Mobile sources: Exhaust emissions from vehicles.

Area sources: Two-dimensional source of diffuse emissions, eg. emissions of methane and ammonia from piggeries and other livestock operations.

Evaporative sources: Volatile liquids that evaporate when not completely enclosed in a tank or other container, and release vapours over time, eg. paints, solvents, pesticides, perfumes, hair sprays, aerosol sprays, and gasoline.

Controlled burns: Practised in forestry management and in agriculture emitting smoke, ash, dust, carbon dioxide, nitrogen oxides, and other air pollutants.

Waste disposal landfills: Landfill gas generated by the action of microbes and chemical reactions, containing methane and carbon dioxide as well as small amounts of ammonia, mercaptans and other sulphides.

Ambient air quality

National authorities are responsible for identifying pollutant threshold values that should not be exceeded, monitoring air quality, introducing measures to lower pollution levels where necessary, as well as communicating air quality information to the public.

In the UK, this framework has been developed through the EU regime, in particular the EU Ambient Air Quality (AAQ) Directive 2008/50/EC. It sets legally binding limits for concentrations of major air pollutants in outdoor air:
• benzene (C6H6)
• carbon monoxide (CO)
• lead (Pb)
• nitrogen dioxide (NO2) and nitrogen oxides (NOx)
• particulate matter (PM-10 and PM-2.5); and
• sulphur dioxide (SO2)

The EU Ambient Air Quality is supplemented by the EU Fourth Air Quality Daughter Directive 2004/107/EC in relation to arsenic, cadmium, mercury, nickel, and polycyclic aromatic hydrocarbons in ambient air.

These provisions are implemented in UK law under:

• the Air Quality Standards Regulations (SI 2010/1001, as amended)
• the Air Quality Standards (Scotland) Regulations (SSI 2010/204, as amended)
• the Air Quality Standards (Wales) Regulations (SI 2010/1433, as amended)
• the Air Quality Standards Regulations (Northern Ireland) (SR 2010/188, as amended)

Relevant authorities must draw up zones and agglomerations according to air quality status and develop air quality plans where necessary. Pollutant levels must not exceed the limit values stipulated under the legislation. Standards require large scale transition to new transport systems, less polluting vehicles, cleaner industry, and rethinking the planning of communities to reduce public exposure to pollutants. These requirements have led to implementation problems.

The Environment Agency, on behalf of Defra and the devolved administrations, run a series of monitoring networks for different pollutants (see the UK AIR: Air Information Resource), involving over 300 monitoring stations with both automatic and non-automatic fixed measurement techniques.

Relevant authorities for the purposes of the Air Quality Standards Regulations:

Secretary of State for Environment, Food and Rural Affairs

Scottish Ministers

Welsh Ministers

Northern Ireland Department of Agriculture, Environment and Rural Affairs (DAERANI)

National emission ceilings

The revised National Emission Ceilings (NEC) Directive 2016/2284/EU establishes reduction targets to national limits for anthropogenic emissions of air pollutants.

These requirements are transposed into UK law by the National Emission Ceilings Regulations 2018 (SI 2018/129). UK targets are:
• SO2 reduction from 2005 levels: 59% for any year between 2020-2029, 88% from 2030
• NOx reduction from 2005 levels: 55% for any year between 2020-2029, 73% from 2030
• non-methane volatile organic compound (NMVOC) reduction from 2005 levels: 32% for any year between 2020-2029, 39% from 2030
• ammonia (NH3) reduction from 2005 levels: 8% for any year between 2020-2029, 16% from 2030
• PM 2.5 reduction from 2005 levels: 16% for any year between 2020-2029, 49% from 2030

The Secretary of State for Environment, Food and Rural Affairs must ensure that national limits are met.

The most recent UK National Air Pollution Control Programme was published in April 2019.

Air quality strategy

A strategic approach to air pollution control was introduced under Part IV of the Environment Act 1995, covering national and local air quality.

The requirements include a duty on the UK government and devolved administrations to produce a national air quality strategy.

The latest UK Clean Air Strategy was published in January 2019. Its measures include:
• ending the sale of new conventional petrol and diesel cars by 2040 – as of May 2020, the government is considering bringing this forward to at least 2035;
• introducing emissions permitting for non-road mobile machinery (NRMM) and intensive farming sectors;
• plans to phase out highly polluting emissions across different transport sectors;
• prohibiting sale of the most polluting fuels and other measures to minimise air pollution in the home;
• maintaining a predictable and improving regulatory framework for industrial emissions; and
• introducing an ‘up to date legislative framework’ for tackling pollution at the national and local level.

Strategies for the devolved jurisdictions have also been published:
• the Cleaner Air for Scotland Strategy, in November 2015; and
• the Clean Air Plan for Wales, in August 2020.

Related guides

Energy & climate change, Industrial regulation, Planning, Hazardous substances, Statutory nuisance, Transport

Local air quality management

The statutory framework (under the Environment Act 1995) for local air quality management (LAQM) in England, Scotland and Wales imposes an obligation on local authorities to undertake an air quality assessment and take action where statutory objectives are not being met. Similar measures exist for Northern Ireland under Part II of the Environment (Northern Ireland) Order 2002 (SI 2002/3153).

Air quality objectives for local authorities – pertaining to benzene (C6H6), 1,3 -Butadiene, carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), particulate matter (PM-10), and sulphur dioxide (SO2) – are set out under:

• the Air Quality (England) Regulations 2000 (SI 2000/928, as amended);
• the Air Quality (Scotland) Regulations 2000 (SSI 2000/97, as amended);
• the Air Quality (Wales) Regulations 2000 (WSI 2000/1940, as amended); and
• the Air Quality Regulations (Northern Ireland) 2003 (SR 2003/342, as amended).

Standards are set in relation to the effect of the pollutant on human health, although effects on the wider environment are also a material consideration. Where a local authority finds places where objectives are not likely to be achieved, it must declare an Air Quality Management Area (AQMA) and devise a Local Air Quality Action Plan (LAQAP) to improve air quality. Those plans can impact industry, development and transport, for instance through the introduction of low emission zones (LEZs) or clean air zones (CAZs).

Clean air strategies

Clean air zones framework for England

Cleaner Air for Scotland Strategy for Scotland

Clean Air Plan for Wales for Wales

Defra guidance on driving in clean air zones in England

Smoke control

The Clean Air Act 1993 addresses air pollution in England, Scotland and Wales from smog caused by widespread burning of coal for residential heating and by industry; it has since been extensively amended.

The Clean Air (Northern Ireland) Order (SI 1981/158, as amended) applies in respect of Northern Ireland; it consolidates the Clean Air Act (Northern Ireland) 1964 and its amendments.

It is an offence for:

• factories and trade premises to emit dark smoke from their chimneys; and
• dark smoke to be emitted from open burning on industrial or trade premises or agricultural land.

The Act also controls the amount of grit and dust emitted from the chimney of non-domestic boilers and some furnaces.

Local authorities can declare the whole or part of their district to be a smoke control zone making it an offence to:

• cause smoke from a chimney; and/or
• obtain or deliver unauthorised fuel, unless the appliance in use is exempt.

Around 50% of households live in smoke control areas.

Exempted appliances and authorised fuels are set out in dedicated Regulations:

Authorised fuels

• the Smoke Control Areas (Authorised Fuels) (England) (No. 2) Regulations 2014 (SI 2014/2366)
• the Smoke Control Areas (Authorised Fuels) (Wales) Regulations 2019 (WSI 2019/50, as amended)
• the Smoke Control Areas (Authorised Fuels) Regulations (Northern Ireland) 2013 (SR 2013/205)

Exempted fireplaces

• the Smoke Control Areas (Exempted Fireplaces) (England) Order 2015 (SI 2015/307)
• the Smoke Control Areas (Exempted Classes of Fireplace) (Wales) Order 2019 (WSI 2019/51)
• the Smoke Control Areas (Exempted Fireplaces) (No.2) Regulations (Northern Ireland) 2013 (SR 2013/292)

The Regulatory Reform (Scotland) Act 2014 introduced amendments which allow for lists to be published by the Scottish Ministers and published in such manner as they consider appropriate (authorised fuels and exempt appliances).


The Environmental Protection Act 1990 provides that smoke, fumes or gases, and any dust, steam, smell or other effluvia arising on industrial, trade or business premises may be considered as a statutory nuisance in England, Scotland and Wales. For nuisance actions to succeed, the offence has to be a cause of material harm; or is persistent or likely to recur.

Similar provisions apply under the Clean Neighbourhoods and Environment Act (Northern Ireland) 2011 in Northern Ireland.

The Statutory Nuisance guide provides further details regarding this area.

Although some activities fall to Defra and the devolved administrations, key measures under the Clean Air Act are generally applied and supervised by local authorities.

Industrial activity

A number of measures have been introduced at EU-level to address air pollution from industrial activities; see Industrial Regulation guide for further details regarding this area. Measures in the UK are delivered through environmental permitting regulations and activity-specific – often pollutant-specific – controls.

Environmental permitting

The environmental permitting regime (EPR) covers a wide range of industries, including fuel production and power generation, metal production and processing, mineral industries, chemical industries, waste disposal and recycling, food and drink processing and intensive livestock installations. Operators must obtain an environmental permit from the appropriate regulator in respect of all activities undertaken. A number of smaller installations, including many solvent using processes, timber activities and crematoria, are regulated for their emissions to air only.

The EPR is governed under:

• the Environmental Permitting (England and Wales) Regulations 2016 (SI 2016/1154)
• the Pollution Prevention and Control (Scotland) Regulations 2012 (SSI 2012/360)
• the Pollution Prevention and Control (Industrial Emissions) Regulations (Northern Ireland) 2013 (SR 2013/160)

These regulations transpose a number of EU-level provisions into domestic law, including:

• the EU Industrial Emissions Directive (IED) 2010/75/EU, which establishes principles for the permitting and control of large industrial installations. It covers emissions to air, including volatile organic compounds (VOCs), among other things.
• the EU Medium Combustion Plant (MCP) Directive 2015/2193/EU, which lays down emission limit values and monitoring requirements to control emissions of sulphur dioxide (SO2), nitrogen oxides (NOx), and dust into the air from MCPs rated at 1 megawatt (MW) or greater.
• the EU Stage I Petrol Vapour Recovery (PVR I) Directive 94/63/EC and the EU Stage II Petrol Vapour Recovery (PVR II) Directive 2009/126/EC, which prevent atmospheric emissions of volatile organic compounds (VOCs) – which readily evaporate contributing to several environmental problems, including excessive levels of toxic benzene (C6H6) in ambient air and photochemical formation of ozone (O3) – by imposing measures on key steps in the storage and distribution of petrol.

Appropriate regulators include the Environment Agency (EA), Natural Resources Wales (NRW), the Scottish Environment Protection Agency (SEPA), and the Northern Ireland Environment Agency (NIEA). Smaller, less complex, installations may also be regulated by local authorities in England and Wales.


Volatile Organic Compounds (VOCs) are organic chemicals that easily vaporize at room temperature, including a wide range of individual substances, such as hydrocarbons – for example, benzene (C6H6) and toluene (C7H8), halocarbons and oxygenates. They are usually grouped into methane and non-methane VOCs and are often found in paints and varnishes.

The Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012 (SI 2012/1715) lays down maximum content limits for VOCs in consumer products. Labels must carry an indication of VOC content. Requirements are derived from the EU Paints Directive 2004/42/EC in the UK.

The environmental permitting regime also limits emissions of VOCs in other industrial activities.

Industries using ozone-depleting substances

Ozone depleting substances (ODS) damage the stratospheric ozone layer, a protective shield against harmful levels of ultraviolet radiation from the sun. They are widely used in refrigerators, air conditioners, fire extinguishers, in dry cleaning, as solvents for cleaning, electronic equipment and as agricultural fumigants.

The production, import, export, marketing, use, recovery, recycling, reclamation and destruction of ODS, such as chlorofluorocarbons and methyl bromide, are set out under:

• the Ozone Depleting Substances Regulation 2015 (SI 2015/168), for England, Scotland and Wales, as well as Northern Ireland in so far as they relate to import and export, and
• the Controls on Ozone-Depleting Substances Regulations (Northern Ireland) 2011 (SR 2011/239)

They provide for the enforcement of the EU ODS Regulation 1005/2009/EC, which prohibits the production of controlled substances, including certain chlorofluorocarbons (CFCs), halons, and hydrochlorofluorocarbons (HCFCs), carbon tetrachloride (CCl4), and methyl bromide (CH3Br), among others.

Measures to address ODS were established at the international level under the 1985 Vienna Convention for the Protection of the Ozone Layer and the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer.

Non-road mobile machinery

The UK framework implementing the revised type-approval testing regime for NRMM – as set out under the EU Non-Road Mobile Machinery (NRMM) Regulation 2016/1628/EU, which sets requirements relating to gaseous and particulate pollutant emission limits – has been introduced under the Non-Road Mobile Machinery (Type-Approval and Emission of Gaseous and Particulate Pollutants) Regulations 2018 (SI 2018/764).

NRMM covers a wide variety of machinery, for example:

• small gardening and handheld equipment;
• construction machinery;
• agricultural and farming machinery; and even

• railcars, locomotives and inland waterway vessels.


Transport is unsurprisingly majorly impacted by air quality legislation, from UK air quality plans dedicated to tackling nitrogen dioxide emissions from road transport, to emissions performance standards impacting the design and manufacture of vehicles.


The Merchant Shipping (Prevention of Air Pollution from Ships) Regulations 2008 (SI 2008/2924, as amended) implement a series of internationally agreed technical standards set out under Annex VI (Regulations for the Prevention of Air Pollution from Ships) to 1973 MARPOL Convention for the Prevention of Pollution from Ships.


Leaded fuel

The Motor Fuel (Composition and Content) Regulations 1999 (SI 1999/3107) banned leaded petrol from 1 January 2000, implementing the requirements of the EU Fuel Quality Directive 98/70/EC. Petrol producers and importers of leaded petrol for classic cars must apply for a permit.


The EU Sulphur Content of Certain Liquid Fuels Directive 2016/802/EU lays down the maximum permitted sulphur content for heavy fuel oil, gas oil, marine gas oil and marine diesel oil in the EU. In the UK, this is implemented through:

• the Merchant Shipping (Prevention of Air Pollution from Ships) Regulations 2008 (SI 2008/2924), for ships
• the Sulphur Content of Liquid Fuels (England and Wales) Regulations 2007 (SI 2007/79)
• the Sulphur Content of Liquid Fuels (Scotland) Regulations 2014 (SSI 2014/258)
• the Sulphur Content of Liquid Fuels Regulations (Northern Ireland) (SR 2007/272).

MARPOL, Annex VI, sets limits on sulphur and nitrogen oxides (SOx and NOx) emissions from ship exhausts and prohibits deliberate emissions of ozone depleting substances (ODS); designated emission control areas set more stringent standards for SOx, NOx, and particulate matter (PM).

Road Vehicles

Emissions performance standards

Emissions performance standards in the UK are derived from legislation set out at the EU level in respect of the design and construction of motor vehicles, through:

• the EU Type Approval of Motor Vehicles Framework Directive 2007/46/EC, which provides a common legal framework for the type approval of cars, vans, trucks, buses and coaches;
• the Road Vehicles (Approval) Regulations 2009 (SI 2009/717), which implement EU Directive 2007/46/EC in domestic UK law;
• the EU CO2 Performance Standards for New Passenger Cars and Light Commercial Vehicles Regulation 2019/631/EU;
• the EU CO2 Performance Standards for Heavy-duty Vehicles Regulation 2019/1242/EU;
• the EU Euro 5 and 6 Regulation 715/2007/EC, the latest in a long series of measures dating back to the 1970s which restrict emissions of pollutants from light motor vehicles;
• the EU Euro VI Regulation 595/2009/EC, which establishes similar controls regarding emissions from heavy-duty vehicles; and
• testing requirements under EU Regulations 2017/1151/EU (regarding the Worldwide Harmonised Light Vehicles Test Procedure) and 2018/1832/EU (regarding real-driving emissions).

The EU Regulations are retained in UK law, and continue to apply in this domestic form to the UK after 31 December 2020.

The Motor Vehicles (Replacement of Catalytic Converters and Pollution Control Devices) Regulations 2009 (SI 2009/1899) further prohibit the supply and installation of non type-approved replacement catalytic converters on certain vehicles that have been approved to EU emissions standards (under the original EU Euro Emissions Directive 70/220/EC through to the Euro 5 and 6 Regulation 715/2007/EC).

Exhaust emissions

The Road Vehicles (Construction and Use) Regulations (SI 1986/1078) regulate the manufacture, equipment and maintenance of new motor vehicles, including setting standards for exhaust emissions for England, Wales and Scotland. The Motor Vehicles (Construction and Use) Regulations (Northern Ireland) 1999 (SR 1999/454) does the same for Northern Ireland.

Emission tests are a mandatory part of the MOT. Police can stop a vehicle on the road if it is producing so much smoke as to be a hazard to other drivers. Smoky buses, coaches and lorries can be reported to DSA, who will notify the operator to clean up their vehicle.

The Driver and Vehicle Standards Agency (DVSA), and the Driver and Vehicles Agency (DVA) in Northern Ireland, also carry out roadside tests and can issue fixed penalties for failing vehicles.

Within air quality management areas (AQMAs), local authorities can also issue fixed penalty notices under:

• the Road Traffic (Vehicle Emissions) (Fixed Penalty) (England) Regulations 2002 (SI 2002/1808)
• the Road Traffic (Vehicle Emissions) (Fixed Penalty) (Wales) Regulations 2003 (WSI 2003/300)
• the Road Traffic (Vehicle Emissions) (Fixed Penalty) (Scotland) Regulations 2003 (SSI 2003/312)

The same Regulations provide for fixed penalties for stationary idling.

Related guides

Energy & climate change, Transport


Transboundary pollution

Pollution doesn’t stop at national borders. International treaties have addressed the issue of transboundary polluting emissions, on the basis that ‘no State has the right to use or permit the use of its territory in such a manner as to cause injury by fumes in or to the territory of another or the properties or persons therein, when the case is of serious consequence and the injury is established by clear and convincing evidence’1.

The 1979 Geneva Convention on Long-Range Transboundary Air Pollution (CLRTAP) (Geneva, 1979) represents the first internationally legally binding instruments dealing with problems of air pollution on a broad regional basis – adopted in response to growing international concern over transboundary movements of acidifying pollutants, particularly in respect of the destruction of Scandinavian forests and lakes. CLRTAP does not set air quality standards or set up liability rules for polluting states. Parties – including the EU and its Member States – to the Convention agree to ‘endeavour to limit and, as far as possible, gradually reduce and prevent air pollution including long-range transboundary air pollution’.

CLRTAP is supplemented by eight protocols, setting national emission limits and reduction targets for certain pollutants:

1984 Geneva Protocol on Long-Term Financing of the Cooperative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP)
1985 Helsinki Protocol on the Reduction of Sulphur Emissions or their Transboundary Fluxes by at least 30 per cent
1988 Sofia Protocol concerning the Control of Nitrogen Oxides or their Transboundary Fluxes
1991 Geneva Protocol concerning the Control of Emissions of Volatile Organic Compounds or their Transboundary Fluxes
1994 Oslo Protocol on Further Reduction of Sulphur Emissions
1998 Aarhus Protocol on Heavy Metals
1998 Aarhus Protocol on Persistent Organic Pollutants (POPs)
1999 Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone

The 1991 Espoo Convention on Environmental Impact Assessment in a Transboundary Context establishes environmental impact assessment obligations onto its parties in relation to major projects that are likely to have a significant adverse environmental impact across boundaries. States should also notify and consult each other.

1 – the harm principle, established in the Trail Smelter arbitrations 1938 and 1941