Air quality law

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Air quality laws govern the emission of air pollutants into the atmosphere. A specialized subset of air quality laws regulate the quality of air inside buildings. Air quality laws are often designed specifically to protect human health by limiting or eliminating airborne pollutant concentrations. Other initiatives are designed to address broader ecological problems, such as limitations on chemicals that affect the ozone layer, and emissions trading programs to address acid rain or climate change. Regulatory efforts include identifying and categorising air pollutants, setting limits on acceptable emissions levels, and dictating necessary or appropriate mitigation technologies.


Air pollutant classification

Air quality regulation must identify the substances and energies which qualify as "pollution" for purposes of further control. While specific labels vary from jurisdiction to jurisdiction, there is broad consensus among many governments regarding what constitutes air pollution. For example, the United States Clean Air Act identifies ozone, particulate matter, carbon monoxide, nitrogen oxides (NOx), sulfur dioxide (SO2), and lead (Pb) as "criteria" pollutants requiring nationwide regulation. [1] EPA has also identified over 180 compounds it has classified as "hazardous" pollutants requiring strict control. [2] Other compounds have been identified as air pollutants due to their adverse impact on the environment (e.g., CFCs as agents of ozone depletion), and on human health (e.g., asbestos in indoor air). [3] A broader conception of air pollution may also incorporate noise, light, and radiation. The United States has recently seen controversy over whether carbon dioxide (CO2) and other greenhouse gases should be classified as air pollutants. [4]

Air quality standards

Air quality standards are legal standards or requirements governing concentrations of air pollutants in breathed air, both outdoors and indoors. Such standards generally are expressed as levels of specific air pollutants that are deemed acceptable in ambient air, and are most often designed to reduce or eliminate the human health effects of air pollution, although secondary effects such as crop and building damage may also be considered. [5] Determining appropriate air quality standards generally requires up-to-date scientific data on the health effects of the pollutant under review, with specific information on exposure times and sensitive populations. It also generally requires periodic or continuous monitoring of air quality.

As an example, the United States Environmental Protection Agency has developed the National Ambient Air Quality Standards (NAAQS) [6] NAAQS set attainment thresholds for sulfur dioxide, particulate matter (PM10 and PM2.5), carbon monoxide, ozone, nitrogen oxides NOx, and lead (Pb) in outdoor air throughout the United States. Another set of standards, for indoor air in employment settings, is administered by the U.S. Occupational Safety and Health Administration. [7]

A distinction may be made between mandatory and aspirational air quality standards. For example, U.S. state governments must work toward achieving NAAQS, but are not forced to meet them. On the other hand, employers may be required immediately to rectify any violation of OSHA workplace air quality standards.

Emission standards

Emission standards are the legal requirements governing air pollutants released into the atmosphere . Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes. They are generally designed to achieve air quality standards and to protect human life. Different regions and countries have different standards for vehicle emissions.

Numerous methods exist for determining appropriate emissions standards, and different regulatory approaches may be taken depending on the source, industry, and air pollutant under review. [8] Specific limits may be set by reference to and within the confines of more general air quality standards. Specific sources may be regulated by means of performance standards, meaning numerical limits on the emission of a specific pollutant from that source category. Regulators may also mandate the adoption and use of specific control technologies, often with reference to feasibility, availability, and cost. Still other standards may be set using performance as a benchmark - for example, requiring all of a specific type of facility to meet the emissions limits achieved by the best performing facility of the group. All of these methods may be modified by incorporating emissions averaging, market mechanisms such as emissions trading, and other alternatives.

For example, all of these approaches are used in the United States. [9] The United States Environmental Protection Agency (responsible for air quality regulation at a national level under the U.S. Clean Air Act, utilizes performance standards under the New Source Performance Standard (NSPS) program. Technology requirements are set under RACT (Reasonably Available Control Technology), BACT (Best Available Control Technology), and LAER (Lowest Achievable Emission Rate) standards. [10] Flexibility alternatives are implemented in U.S. programs to eliminate acid rain, protect the ozone layer, achieve permitting standards, and reduce greenhouse gas emissions. [11]

Control technology requirements

In place of or in combination with air quality standards and emission control standards, governments may choose to reduce air pollution by requiring regulated parties to adopt emissions control technologies (i.e., technology that reduces or eliminates emissions). Such devices include but are not limited to flare stacks, incinerators, catalytic combustion reactors, selective catalytic reduction reactors, electrostatic precipitators, baghouses, wet scrubbers, cyclones, thermal oxidizers, Venturi scrubbers, carbon adsorbers, and biofilters.

The selection of emissions control technology may be the subject of complex regulation that may balance multiple conflicting considerations and interests, including economic cost, availability, feasibility, and effectiveness. [12] The various weight given to each factor may ultimately determine the technology selected. The outcome of an analysis seeking a technology that all players in an industry can afford could be different from an analysis seeking to require all players to adopt the most effective technology yet developed, regardless of cost. For example, the United States Clean Air Act contains several control technology requirements, including Best Available Control Technology (BACT) (used in New Source Review), Reasonably Available Control Technology (RACT) (existing sources), Lowest Achievable Emissions Rate (LAER) (used for major new sources in non-attainment areas), and Maximum Achievable Control Technology (MACT) standards.


Air quality laws may take the form of bans. While arguably a class of emissions control law (where the emission limit is set to zero), bans differ in that they may regulate activity other than the emission of a pollutant itself, even though the ultimate goal is to eliminate the emission of the pollutant.

A common example is a burn ban. [13] Residential and commercial burning of wood materials may be restricted during times of poor air quality, eliminating the immediate emission of particulate matter and requiring use of non-polluting heating methods. A more significant example is the widespread ban on the manufacture of dichlorodifluoromethane (Freon)), formerly the standard refrigerant in automobile air conditioning systems. This substance, often released into the atmosphere unintentionally as a result of refrigerant system leaks, was determined to have a significant ozone depletion potential, and its widespread use to pose a significant threat to the Earth's ozone layer. Its manufacture was prohibited as part of a suite of restrictions adopted internationally in the Montreal Protocol to the Vienna Convention for the Protection of the Ozone Layer. Still another example is the ban on use of asbestos in building construction materials, to eliminate future exposure to carcinogenic asbestos fibers when the building materials are disturbed. Other international regulatory areas, often under the auspices of the UN or EU, have also initiated work on phasing out the use of fossil based fuel. For example, the UN's International Maritime Organization (IMO) are beginning to develop and adopt regulatory measures (MARPOL 73/78) to decarbonize international shipping. [14]

Data collection and access

Air quality laws may impose substantial requirements for collecting, storing, submitting, and providing access to technical data for various purposes, including regulatory enforcement, public health programs, and policy development.

Data collection processes may include monitoring ambient air for the presence of pollutants, directly monitoring emissions sources, or collecting other quantitative information from which air quality information may be deduced. For example, local agencies may employ a particulate matter sampler to determine ambient air quality in a locality over time. Fossil power plants may required to monitor emissions at a flue-gas stack to determine quantities of relevant pollutants emitted. Automobile manufacturers may be required to collect data regarding car sales, which, when combined with technical specifications regarding fuel consumption and efficiency, may be used to estimate total vehicle emissions. In each case, data collection may be short- or long-term, and at varying frequency (e.g., hourly, daily).

Air quality laws may include detailed requirements for recording, storing, and submitting relevant information, generally with the ultimate goal of standardizing data practices in order to facilitate data access and manipulation at a later time. [15] Precise requirements may be very difficult to determine without technical training and may change over time in response to, for example, changes in law, changes in policy, changes in available technology, and changes in industry practice. Such requirements may be developed at a national level and reflect consensus or compromise between government agencies, regulated industry, and public interest groups.

Once air quality data are collected and submitted, some air quality laws may require government agencies or private parties to provide the public with access to the information - whether the raw data alone, or via tools to make the data more useful, accessible, and understandable. Where public access mandates are general, it may be left to the collecting agency to decide whether and to what extent the data is to be centralized and organized. For example, the United States Environmental Protection Agency, National Oceanic and Atmospheric Administration, National Park Service, and tribal, state, and local agencies coordinate to produce an online mapping and data access tool called AirNow, which provides real-time public access to U.S. air quality index information, searchable by location.

Once data are collected and published, they may be used as inputs in mathematical models and forecasts. For example, atmospheric dispersion modeling may be employed to examine the potential impact of new regulatory requirements on existing populations or geographic areas. Such models in turn could drive changes in data collection and reporting requirements.


Proponents of air quality law argue that they have caused or contributed to major reductions in air pollution, with concomitant human health and environmental benefits, even in the face of large-scale economic growth and increases in motor vehicle use. [16] On the other hand, controversy may arise over the estimated cost of additional regulatory standards. [17]

Arguments over cost, however, cut both ways. For example, the "estimates that the benefits of reducing fine particle and ground level ozone pollution under the 1990 Clean Air Act amendments will reach approximately $2 trillion in 2020 while saving 230,000 people from early death in that year alone." According to the same report, 2010 alone the reduction of ozone and particulate matter in the atmosphere prevented more than 160,000 cases of premature mortality, 130,000 heart attacks, 13 million lost work days and 1.7 million asthma attacks. [18] Criticisms of EPA's methodologies in reaching these and similar numbers are publicly available. [19]

Around the world

International law

International law includes agreements related to trans-national air quality, including greenhouse gas emissions:


With some industry-specific exceptions, Canadian air pollution regulation was traditionally handled at the provincial level. [21] However, under the authority of the Canadian Environmental Protection Act, 1999, the country has recently enacted a national program called the Canadian Air Quality Management System (AQMS). The program includes five main regulatory mechanisms: the Canadian Ambient Air Quality Standards (CAAQS); Base Level Industrial Emission Requirements (BLIERs) (emissions controls and technology); management of local air quality through the management of Local Air Zones; management of regional air quality through the management of Regional Airsheds; and collaboration to reduce mobile source emissions. [22]

The Canadian government has also made efforts to pass legislation related to the country's greenhouse gas emissions. It has passed laws related to fuel economy in passenger vehicles and light trucks, heavy-duty vehicles, renewable fuels, and the energy and transportation sectors. [23]


China, with severe air pollution in mega-cities and industrial centers, particularly in the north, has adapted the Airborne Pollution Prevention and Control Action Plan which aims for a 25% reduction in air pollution by 2017 from 2012 levels. Funded by $277 billion from the central government, the action plan targets PM 2.5 particulates which affect human health. [24]

New Zealand

New Zealand passed its Clean Air Act 1972 in response to growing concerns over industrial and urban air pollution. [25] That Act classified sources, imposed permitting requirements, and created a process for determining requisite control technology. Local authorities were authorized to regulate smaller polluters. Within the Christchurch Clean Air Zone, burn bans and other measures were effected to control smog.

The Clean Air Act 1972 was replaced by the Resource Management Act 1991. The act did not set air quality standards, but did provide for national guidance to be developed. This resulted in the promulgation of New Zealand's National Environmental Standards for Air Quality in 2004 with subsequent amendments. [26]

United Kingdom

In response to the Great Smog of 1952, the British Parliament introduced the Clean Air Act 1956. This act legislated for zones where smokeless fuels had to be burnt and relocated power stations to rural areas. The Clean Air Act 1968 [27] introduced the use of tall chimneys to disperse air pollution for industries burning coal, liquid or gaseous fuels. [28]

The Clean Air Act was updated in 1993. [29] The biggest domestic impact comes from Part III, Smoke Control Areas, which are designated by local authorities and can vary by street in large towns.

United States

The primary law regulating air quality in the United States is the U.S. Clean Air Act. The law was initially enacted as the Air Pollution Control Act of 1955. Amendments in 1967 and 1970 (the framework for today's U.S. Clean Air Act) imposed national air quality requirements, and placed administrative responsibility with the newly created Environmental Protection Agency. Major amendments followed in 1977 and 1990. State and local governments have enacted similar legislation, either implementing federal programs or filling in locally important gaps in federal programs.

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<span class="mw-page-title-main">Exhaust gas</span> Gases emitted as a result of fuel reactions in combustion engines

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The National Emission Standards for Hazardous Air Pollutants (NESHAP) are air pollution standards issued by the United States Environmental Protection Agency (EPA). The standards, authorized by the Clean Air Act, are for pollutants not covered by the National Ambient Air Quality Standards (NAAQS) that may cause an increase in fatalities or in serious, irreversible, or incapacitating illness.

<span class="mw-page-title-main">National Ambient Air Quality Standards</span> US EPA limits on certain air pollutants

The U.S. National Ambient Air Quality Standards are limits on atmospheric concentration of six pollutants that cause smog, acid rain, and other health hazards. Established by the United States Environmental Protection Agency (EPA) under authority of the Clean Air Act, NAAQS is applied for outdoor air throughout the country.

<span class="mw-page-title-main">Air quality index</span> Measure of air pollution

An air quality index (AQI) is used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. AQI information is obtained by averaging readings from an air quality sensor, which can increase due to vehicle traffic, forest fires, or anything that can increase air pollution. Pollutants tested include ozone, nitrogen dioxide, sulphur dioxide, among others.

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<span class="mw-page-title-main">Clean Air Act (United States)</span> United States federal law to control air pollution

The Clean Air Act (CAA) is the United States' primary federal air quality law, intended to reduce and control air pollution nationwide. Initially enacted in 1963 and amended many times since, it is one of the United States' first and most influential modern environmental laws.

To protect the environment from the adverse effects of pollution, many nations worldwide have enacted legislation to regulate various types of pollution as well as to mitigate the adverse effects of pollution. At the local level, regulation usually is supervised by environmental agencies or the broader public health system. Different jurisdictions often have different levels regulation and policy choices about pollution. Historically, polluters will lobby governments in less economically developed areas or countries to maintain lax regulation in order to protect industrialisation at the cost of human and environmental health.

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<span class="mw-page-title-main">Water quality law</span>

Water quality laws govern the protection of water resources for human health and the environment. Water quality laws are legal standards or requirements governing water quality, that is, the concentrations of water pollutants in some regulated volume of water. Such standards are generally expressed as levels of a specific water pollutants that are deemed acceptable in the water volume, and are generally designed relative to the water's intended use - whether for human consumption, industrial or domestic use, recreation, or as aquatic habitat. Additionally, these laws provide regulations on the alteration of the chemical, physical, radiological, and biological characteristics of water resources. Regulatory efforts may include identifying and categorizing water pollutants, dictating acceptable pollutant concentrations in water resources, and limiting pollutant discharges from effluent sources. Regulatory areas include sewage treatment and disposal, industrial and agricultural waste water management, and control of surface runoff from construction sites and urban environments. Water quality laws provides the foundation for regulations in water standards, monitoring, required inspections and permits, and enforcement. These laws may be modified to meet current needs and priorities.

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Entergy Corp. v. Riverkeeper, Inc., 556 U.S. 208 (2009), is a decision by the United States Supreme Court that reviewed the Environmental Protection Agency's (EPA) interpretation of the Clean Water Act regulations with regard to cooling water intakes for power plants. Existing facilities are mandated to use the "Best Technology Available" to "minimize the adverse environmental impact." The issue was whether the agency may use a cost–benefit analysis (CBA) in choosing the Best Available Technology or (BAT) to meet the National Performance Standards (NPS).

<span class="mw-page-title-main">Mobile source air pollution</span>

Mobile source air pollution includes any air pollution emitted by motor vehicles, airplanes, locomotives, and other engines and equipment that can be moved from one location to another. Many of these pollutants contribute to environmental degradation and have negative effects on human health. To prevent unnecessary damage to human health and the environment, environmental regulatory agencies such as the U.S. Environmental Protection Agency have established policies to minimize air pollution from mobile sources. Similar agencies exist at the state level. Due to the large number of mobile sources of air pollution, and their ability to move from one location to another, mobile sources are regulated differently from stationary sources, such as power plants. Instead of monitoring individual emitters, such as an individual vehicle, mobile sources are often regulated more broadly through design and fuel standards. Examples of this include corporate average fuel economy standards and laws that ban leaded gasoline in the United States. The increase in the number of motor vehicles driven in the U.S. has made efforts to limit mobile source pollution challenging. As a result, there have been a number of different regulatory instruments implemented to reach the desired emissions goals.

The Ventura County Air Pollution Control District (VCAPCD), formed in 1968, is the air pollution agency responsible mainly for regulating stationary sources of air pollution for Ventura County. The District was formed by the Board of Supervisors in response to the county's first air pollution study which identified Ventura County as having a severe air quality problem.

Utility Air Regulatory Group v. Environmental Protection Agency, 573 U.S. 302 (2014), was a US Supreme Court case regarding the Environmental Protection Agency's regulation of air pollution under the Clean Air Act.

CMAQ is an acronym for the Community Multiscale Air Quality Model, a sophisticated three-dimensional Eulerian grid chemical transport model developed by the US EPA for studying air pollution from local to hemispheric scales. EPA and state environmental agencies use CMAQ to develop and assess implementation actions needed to attain National Ambient Air Quality Standards (NAAQS) defined under the Clean Air Act. CMAQ simulates air pollutants of concern—including ozone, particulate matter (PM), and a variety of air toxics — to optimize air quality management. Deposition values from CMAQ are used to assess ecosystem impacts such as eutrophication and acidification from air pollutants. In addition, the National Weather Service uses CMAQ to produce twice-daily forecast guidance for ozone air quality across the U.S. CMAQ unites the modeling of meteorology, emissions, and chemistry to simulate the fate of air pollutants under varying atmospheric conditions. Other kinds of models—including crop management and hydrology models— can be linked with the CMAQ simulations, as needed, to simulate pollution more holistically across environmental media.


  1. U.S. EPA, What Are the Six Common Air Pollutants?
  2. U.S. EPA, Original list of hazardous air pollutants.
  3. U.S. EPA, Air Pollutants Archived June 23, 2014, at the Wayback Machine .
  4. See Massachusetts v. Environmental Protection Agency .
  5. See generally U.S. EPA, Air Quality.
  6. See U.S. EPA NAAQS Archived 2010-12-10 at the Wayback Machine .
  7. See U.S. OSHA, Indoor Air Quality.
  8. See generally, U.S. EPA Emissions page.
  9. See generally, U.S. EPA, Setting Emissions Standards Based on Technology Performance, Building Flexibility with Accountability into Clean Air Programs, and linked materials.
  10. See U.S. EPA, Emissions page.
  11. See U.S. EPA, EPA's Greenhouse Gas Emissions Reductions.
  12. See, for example, U.S. EPA's Industrial Boiler process and linked materials.
  13. See, e.g., Puget Sound Air Resources Board Burn Bans Archived 2015-06-26 at the Wayback Machine .
  14. Jesper Jarl Fanø (2019). Enforcing International Maritime Legislation on Air Pollution through UNCLOS. Hart Publishing. Part IV (Ch. 16-18)
  15. See, for example Massachusetts EPA Air Permit & Reporting Toolkit Forms.
  16. See Union of Concerned Scientists, The Clean Air Act.
  17. See, e.g., W. Koch, Obama, EPA sued for nixing tougher ozone rules (USA Today).
  18. Enesta Jones (2011-03-01). "EPA Report Underscores Clean Air Act's Successful Public Health Protections/Landmark law saved 160,000 lives in 2010 alone". Retrieved 22 March 2012.
  19. See generally EPA air quality dockets at
  20. Georgia Basin-Puget Sound International Airshed Strategy, Vancouver, Statement of Intent, 2002
  21. See Environmental Law in Canada, Blakes Lawyers (2012) Archived 2015-07-01 at the Wayback Machine .
  22. Overview available at Newfoundland Labrador Department of Environment and Conservation Archived 2015-07-01 at the Wayback Machine .
  23. See [ Canada's Action on Climate Change].
  24. "Airborne Pollution Prevention and Control Action Plan (2013-17)". August 16, 2013. Retrieved December 10, 2014.
  25. Historical information in this section adapted from The State of New Zealand’s Environment 1997, Chapter 6.
  26. See About the NES.
  27. "Watership Down author Richard Adams mentions his role in the Clean Air Act 1968". Archived from the original on 2010-01-09. Retrieved 2010-01-16.
  28. "United Kingdom's Clean Air Acts". Archived from the original on 2010-01-26. Retrieved 2010-01-16.
  29. Clean Air Act 1993