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 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 (NO_x), sulfur dioxide (SO₂), and lead (Pb) as "criteria" pollutants requiring nationwide regulation. EPA has also identified over 180 compounds it has classified as "hazardous" pollutants requiring strict control. 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). 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.

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. 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) NAAQS set attainment thresholds for sulfur dioxide, particulate matter (PM₁₀ and PM_2.5), carbon monoxide, ozone, nitrogen oxides NO_x, 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.

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 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. 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. 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. Flexibility alternatives are implemented in U.S. programs to eliminate acid rain, protect the ozone layer, achieve permitting standards, and reduce greenhouse gas emissions.