CHAPTER 2: Relevant Air Quality Standards and Regulations
The following sections provide overviews of the predominant air quality standards and regulations as they apply to airports and airport emission sources in the United States.
2.1 CLEAN AIR ACT (CAA)
For decades following the establishment of commercial-service airports in the United States, the common complaint from neighboring communities was aircraft noise, which was considered more of an annoyance than a health concern. This focus on noise continued through the introduction of the large commercial turboprop-engine aircraft in the 1950s and the turbofan engines in the 1960s. However, with the enactment of the Air Pollution Control Act in 1955, the Clean Air Act (CAA) in 1970, and the Clean Air Act Amendments (CAAA) in 1977 and 1990, emissions and air quality were given increasingly greater scrutiny. The 1990 CAAA brought sweeping changes that included various measures to further control and regulate emissions, including airport emission sources.
Standards Versus Pollutants
Primary and Secondary Standards refer to the ambient standards established as the National Ambient Air Quality Standards (NAAQS) for criteria pollutants for the protection of public health (primary standards) and protection of the environment (secondary standards).
Primary and Secondary Pollutants refer to whether pollutants are emitted directly from a source (primary pollutants) or formed in the atmosphere through chemical reactions and/or physical processes of the primary pollutants (secondary pollutants).
2.2 NATIONAL AMBIENT AIR QUALITY STANDARDS (NAAQS)
Under the CAA, ambient air concentration limits of six (6) criteria pollutants having adverse human health and environmental effects were established by the EPA as the NAAQS. The current NAAQS are summarized in Table 2-1.
Table 2-1. National Ambient Air Quality Standards.
| Pollutant | Averaging Period | Primary Standards | Secondary Standards | ||
|---|---|---|---|---|---|
| Carbon Monoxide (CO) | 8 hours | 9 ppm | None | ||
| 1 hour | 35 ppm | ||||
| Lead (Pb) | Rolling 3-month average | 0.15 µg/m3 | Same as Primary | ||
| Nitrogen Dioxide (NO2) | Annual | 53 ppb | Same as Primary | ||
| 1 hour | 100 ppb | None | |||
| Particulate Matter | PM10 | 24 hours | 150 µg/m3 | Same as Primary | |
| PM2.5 | Annual | 9.0 µg/m3 | 15.0 µg/m3 | ||
| 24 hours | 35 µg/m3 | Same as Primary | |||
| Ozone (O3) | 8 hours | 0.070 ppm | Same as Primary | ||
| Sulfur Dioxide (SO2) | 1 hour | 75 ppb | 3-hour | 0.5 ppm | |
Source: https://www.epa.gov/criteria-air-pollutants/naaqs-table
The NAAQS reflect concentration values that have been developed through various scientific and health studies. The EPA sets two types of NAAQS for each criteria pollutant: primary and secondary standards. Primary standards are designed to protect public health, including sensitive populations such as asthmatics, children, and the elderly. Secondary standards address public welfare by protecting against the reduction of visibility and damage to animals, crops, vegetation, and buildings. The NAAQS undergo thorough periodic reviews, as required by the CAA, and have been revised several times as a result of these reviews. Most recently, EPA strengthened the PM2.5 primary annual standard from 12 µg/m3 down to 9 µg/m3 in February 2024. The current standards can be found on the EPA website at https://www.epa.gov/criteria-air-pollutants.
The EPA determines the attainment status for each area in the United States for each of the NAAQS based on monitored pollutant concentrations and may also evaluate other information that can be used to characterize air quality in the area, such as air quality modeling. The following designations are used to signify the status of each area:
- Nonattainment—Any area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet) the national primary or secondary ambient air quality standard for the pollutant.
- Attainment—Any area that meets the national primary or secondary air quality standard for the pollutant.
- Unclassifiable—Any area that cannot be classified on the basis of available information as meeting or not meeting the national primary or secondary air quality standards for the pollutant, generally due to lack of monitoring data in that area.
Nonattainment areas may also be further designated as marginal, moderate, serious, severe, or extreme depending on how much the area’s concentrations exceed the ambient standards. An
airport must comply with state and federal regulations based on the attainment status of the area where it is located.
While the NAAQS include PM10 and PM2.5, currently there are no standards for much smaller PM size ranges, such as UFPs. UFPs are of concern because they can travel deep in the lungs. In addition, they can absorb a substantial amount of toxic substances, due to their high surface to volume ratio. UFPs have such a light mass they are described by particle number concentration (number of UFPs/volume), unlike larger particles described by mass concentration. Mass concentration of larger PM do not equate to UFP concentrations, i.e., a high PM10 concentration is not indicative of low or high UFP concentrations. It is difficult to propose limits and standards for UFPs because of the limited availability of ambient measurements of that pollutant needed for health studies. Moreover, UFPs quickly agglomerate into larger particles in ambient air, so concentrations tend to decline significantly with distance from a source, making it difficult to establish population exposures.
Similarly, there are no NAAQS for HAPs also known as air toxics. However, EPA and many states have established health benchmarks for cancer (unit risk values) and non-cancer effects (e.g., EPA’s Reference Concentrations [RfCs]) associated with inhalation of these pollutants. In addition, the Occupational Safety & Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) have concentration standards for workplaces in the form of permissible exposure limits (PELs) and recommended exposure limits (RELs). These recommended limits would apply to airport employees.
2.3 STATE IMPLEMENTATION PLAN
The 1970 CAA required states to develop a State Implementation Plan (SIP) to implement the NAAQS and ensure the standards are met and maintained. A SIP is intended to serve two purposes--to demonstrate how a state’s air quality management program will implement the NAAQS and to identify the emission control strategies the state will rely on to meet and/or maintain the NAAQS. An inventory of estimated emissions from airports located within each state, and the emissions projected to occur in the future from those airports, are included in the states’ SIP budgets and are considered in the states’ plans to reduce further emissions of harmful pollutants and maintain pollutant concentrations at an acceptable level.
2.4 GENERAL AND TRANSPORTATION CONFORMITY
The General Conformity Rule was established under the CAA and sets emissions thresholds above which an air quality assessment is required for new projects in areas of the country already experiencing poor air quality (i.e., within nonattainment areas or areas that have been redesignated from nonattainment to attainment of the NAAQS, known as maintenance areas). Similarly, Transportation Conformity requirements, also established under the CAA, ensure that federally funded highway or transit activities would not contribute to, cause new violations of, or delay timely attainment of the NAAQS. To assess the impact of new projects on a SIP, either General Conformity or Transportation Conformity evaluations need to be performed, depending on the project type. Most airport projects require General Conformity evaluations that include the quantification of the expected net emissions from a project (i.e., emissions beyond the status quo or no-build case). These are compared to established de minimis levels to determine if they will have a significant impact on the state’s overall emissions inventory. Depending on the magnitude of the project emissions, an evaluation of its compliance with the SIP may need to be made (i.e., whether the regional emissions budget can absorb the project emissions). In addition, atmospheric
dispersion modeling may need to be conducted to better assess the impact of the expected project emissions. If a project is found to conform to a SIP, it is not expected to cause or contribute to new air quality violations or delay the area from timely attainment of the NAAQS. If a project does not conform, emission mitigation measures may need to be adopted in order for the project to be approved.
2.5 STATIONARY SOURCE EMISSIONS STANDARDS AND PERMITS
To control emissions, the EPA sets New Source Performance Standards (NSPS), that apply to stationary sources of emissions on a category-specific basis. The NSPS typically include emissions limitations (e.g., 0.60 pounds of nitrogen oxides (NOx) per million BTU of coal for steam electric power plants), which are often more stringent for new sources than for existing sources in that category. Similar to the NSPS, the National Emission Standards for Hazardous Air Pollutants (NESHAP) are established to control mass emissions of HAPs through technology-based standards for each regulated facility or process type. These standards apply to equipment used at airports such as power generators and boilers. Section 112 of Title I of the CAA includes provisions for implementing NESHAP and lists each of the close to 200 HAP species, some of which are listed below:
- Acetaldehyde,
- Benzene,
- 1,3-Butadiene,
- Formaldehyde,
- Toluene,
- Trichloroethylene, and
- Lead compounds.
The full list can be found at the EPA air toxics website, https://www.epa.gov/haps/initial-list-hazardous-air-pollutants-modifications. Emissions and concentrations of HAPs species will vary by airport, with many below the detection limits of ambient monitoring and sampling equipment. It should be noted that lead is both a criteria pollutant and a HAP.
The New Source Review (NSR) air permitting program was established as part of the CAAA. NSR requires sources to obtain preconstruction permits that set emissions and/or operational limits and establish procedures for demonstrating compliance with those limits. Depending on the projected emissions, equipment size, and air quality status of the region, sources including airports must apply for one of three types of NSR permits: prevention of significant deterioration (PSD), nonattainment NSR, and minor NSR.
The 1990 CAAA require facility-wide Title V operating permits for major and some smaller air pollution sources, including airports. Title V permits are legally enforceable documents designed to improve compliance by clarifying what facilities must do to control air pollution and include all air pollution control requirements from federal or state regulations that apply to a source. Title V permits are usually issued by state agencies. Airports must follow the requirements specified in their Title V permits, including recordkeeping and reporting.
2.6 MOBILE SOURCE EMISSIONS STANDARDS
In addition to emission standards for stationary sources, EPA also regulates emissions from mobile source engines, including aircraft, vehicles, and ground support equipment (GSE).
Information on these emission standards can be found at https://www.epa.gov/regulations-emissions-vehicles-and-engines. These standards apply to newly manufactured vehicles or engines with the applicable standard dependent on a vehicle or engine’s model year, size, power and/or use class, with standards generally increasing in stringency over time. These regulations target criteria pollutant and GHG emissions from vehicle or engine exhaust, and in some cases evaporative emissions. EPA most recently updated the standards for cars, sport utility vehicles, light and medium-duty large pickup trucks, and vans in 2024, with the regulations applying to model years 2027 through 2032. For certain categories of aircraft engines, EPA has established regulations for emissions of PM, NOx, and CO2 that align with the International Civil Aviation Organization (ICAO) standards.
Pursuant to section 231(a) of the CAA, EPA (2023) issued a finding that engine emissions of lead from certain aircraft cause or contribute to the lead air pollution that may reasonably be anticipated to endanger public health and welfare. As a result of this endangerment finding, EPA is now directed to propose and promulgate regulatory standards for lead emissions from certain aircraft engines. Under their own authority, FAA is now obligated to develop standards that address the composition or chemical or physical properties of an aircraft fuel or fuel additive to control or eliminate aircraft lead emissions. Separate from the endangerment finding, since 2022, the FAA is also actively partnering with the GA industry under the Eliminate Aviation Gasoline Lead Emissions (EAGLE) initiative to safely eliminate lead emissions from aviation gasoline by the end of 2030.
2.7 NATIONAL ENVIRONMENTAL POLICY ACT (NEPA)
Along with the CAA, the National Environmental Policy Act (NEPA) was enacted in 1970 to serve as a national policy on protecting the environment—requiring environmental evaluations for federal actions with significant impacts on the environment. To comply with NEPA, the FAA is required to provide an accounting of emissions projected to occur from aircraft and other sources of harmful emissions at airports when seeking to expand or improve operations. As part of the NEPA process, FAA is required to evaluate all potential environmental impacts caused by an action at an airport by comparing build and alternative cases with those of the corresponding no-build (baseline) case.
NEPA’s policy and guidance encompass air quality, climate change, health impacts, and EJ. NEPA reviews consider EJ concerns by meaningful engagement, public participation processes, screening analyses, and government-to-government consultation. Health Impact Assessments (HIA) use evidence-based health data to make recommendations for policy. An HIA evaluates how a proposed action might impact the health of the affected population, using qualitative and quantitative evidence and analytical methods along with stakeholder input, and provides decision-makers with information on the potential health outcomes of the proposed action before a decision is made. HIAs are used in the NEPA process to create an environmental impact statement (EIS) and/or assessment.
2.8 ENVIRONMENTAL JUSTICE (EJ)
As defined by Executive Order 14096 (Revitalizing our Nation’s Commitment to Environmental Justice for All, 2023), EJ is the “just treatment and meaningful involvement of all people, regardless of income, race, color, national origin, Tribal affiliation, or disability, in agency decision-making and other federal activities that affect human health and the environment so that people:
- are fully protected from disproportionate and adverse human health and environmental effects (including risks) and hazards, including those related to climate change, the cumulative impacts of environmental and other burdens, and the legacy of racism or other structural or systemic barriers; and
- have equitable access to a healthy, sustainable, and resilient environment in which to live, play, work, learn, grow, worship, and engage in cultural and subsistence practices.”
Fair treatment means not disproportionately placing the burden of negative environmental impacts on any population. Meaningful involvement requires informed decision-making with stakeholder and community participation.
EJ concerns need to be considered for airport developments subject to FAA approval. In line with NEPA requirements, Executive Orders 14096 and 12898 (Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations), and DOT Order 5610.2 (Department of Transportation Actions to Address Environmental Justice in Minority Populations and Low-Income Populations), the FAA must determine whether the area near a proposed airport project has minority or low-income communities and whether the environmental impacts of the proposed development disproportionately affect these communities. EJ concerns associated with airports are numerous: human health, air quality, water quality, light pollution, noise pollution, traffic, and safety. Dispersion modeling and emission monitoring have shown that aircraft emissions travel into local airport communities, potentially leading to detrimental health impacts for residents of the airport communities.
2.9 INDOOR AIR POLLUTION
The importance of indoor air quality received heightened awareness during the global COVID19 pandemic. Implementation of enhanced measures at airports to reduce transmission of COVID19, such as improved HVAC systems, filtration, and faster turnover of indoor air, also serve as methods for improving indoor air quality at airports from causes of indoor air pollution. Since airport employees spend significant amounts of time in the airports, the health impacts of poor indoor air quality would be pronounced from increased exposure to these pollutants. It’s also possible that frequent passengers or passengers with extended stays could experience health impacts. While not the main focus for airports when evaluating health impacts from air pollutants, indoor air still needs to be considered to allow for a comprehensive understanding of potential public health impacts from airport air pollution.
While the NAAQS are set to protect and promote human health and welfare from ambient air quality impacts, EPA currently does not regulate indoor air quality although EPA does offer guidance (https://www.epa.gov/indoor-air-quality-iaq) on educating and helping the public reduce exposures to indoor pollutants. Sources of indoor air pollution at airports include engine exhaust from aircraft, equipment, and vehicles as well as indoor sources including smoking, indoor combustion (such as for food preparation), volatile organic compounds (VOCs) from paints, markings, solvents, cleaning solutions, and indoor building materials. In addition to these sources, inadequate ventilation increases levels of indoor air pollutants because insufficient outdoor air is available for diluting indoor air pollutant concentrations. Thermal conditions (temperature, airflow, and relative humidity) can impact indoor air quality in two ways: (1) optimizing indoor humidity, airflow, and temperature can improve indoor air quality and (2) building materials can release pollutants under high temperature conditions. In extreme cases, indoor pollution can lead to sick building syndrome or building related illness.
OSHA sets standards for specific indoor air contaminants and provides limits to an employee’s exposure to such contaminants through its Standard 29 CFR 1910.1000, Air Contaminants. The listed air contaminants in this standard include all of the criteria air pollutants as well as numerous other substances. This standard sets 8-hour time weighted average exposure limits for employees as well as acceptable ceiling concentrations of these contaminants. These standards are intended to “address potential hazardous conditions leading to serious physical harm or death” and require employers to provide a safe place of employment for their employees. In addition, several organizations have developed standards aimed at improving indoor air quality in buildings. Some organizations encourage improved indoor air through various certification levels. Others provide information and guidance on best practices. Two examples follow.
- The International Well Building Institute has developed WELL Building Standards focused on the people in the building. The air standards under this system encompass 29 criteria for industrial buildings, including specific standards for formaldehyde, VOCs, CO, PM2.5, PM10, ozone, and radon. Other air criteria include smoking bans, ventilation and filtration specifications, mold control, and asbestos and lead restrictions. Buildings are then certified based on how well they meet these and other criteria with a goal of promoting human health and well-being, based on research and development and best practices.
- The International Society of Indoor Air Quality and Climate (ISIAQ) is an international, multidisciplinary organization supporting the creation of healthy, comfortable, and productive indoor environments. The organization works to “advance the science and technology of indoor air quality and climate as it relates to indoor environmental design, construction, operation and maintenance, air quality measurement and health sciences.” This organization provides a database of indoor environmental quality guidelines from across the world and develops its recommendations for indoor environmental quality guidelines.
