Air Quality 101


The Clean Air Act (CAA) is a law created to protect public health and welfare (e.g., harm the environment and cause property damage) through protecting and improving air quality. The CAA is the legal bases for a national air pollution control program which has evolved over time.

The Air Pollution Control Act of 1955

  • First federal air pollution legislation. Funded research for scope and sources of air pollution

Clean Air Act of 1963

  • Authorized the development of a national program to address air pollution related environmental problems and research into techniques to monitor and control air pollution.

Air Quality Act of 1967

  • Authorized enforcement procedures for air pollution problems involving interstate transport of pollutants and expanded research activities.

Clean Air Act 1970 (U.S. Environmental Protection Agency established the same year)

  • Authorized the establishment of National Ambient Air Quality Standards; authorized the establishment of New Source Performance Standards for new and modified stationary sources; authorized the establishment of National Emission Standards for Hazardous Air Pollutants; and authorized requirements for control of motor vehicle emissions. Established requirements for State Implementation Plans to achieve the National Ambient Air Quality Standards and increased enforcement authority.

1977 Amendments to the Clean Air Act of 1970

  • Regarding the National Ambient Air Quality Standards, authorized provisions related to the Prevention of Significant Deterioration of air quality for areas meeting the standards (attainment areas) and provisions related to areas not meeting the standards (non-attainment areas).

1990 Amendments to the Clean Air Act of 1970

  • Authorized programs for Acid Deposition Control; authorized a program to control 187 toxic pollutants, including those previously regulated by the National Emission Standards for Hazardous Air Pollutants. Established permit program requirements and a program to phase out the use of ozone-depleting chemicals. Expanded and modified provisions concerning the attainment of National Ambient Air Quality Standards and enforcement authority.


Title V Permit Program

As applicable to the University – main campus, the CAA authorized Environmental Protection Agency (EPA) to establish national ambient air quality standards for certain common and widespread pollutants based on the latest science. EPA set air quality standards for six common “criteria pollutants”: particulate matter, ozone, sulfur dioxide, nitrogen dioxide, carbon monoxide, and lead. Additionally, EPA was authorized to create emission standards to reduce emissions from 187 hazardous air pollutants (HAP) and develop practices for ozone depleting chemicals.

One method EPA uses to improving air quality is through the 1990 Clean Air Act, Title V – Permits which authorized EPA to create a national operating permit program. There are multiple criteria to determine if a business is required to obtain a Title V permit before an air pollutant source can be constructed and operated. If it is determined that a Title V permit is required, the permit is classified into a category such as major or minor based on the potential pollutant emission. The University is permitted as a Title V major source due to potential emissions of 100 tpy of any regulated pollutant, 10 tpy of any single HAP, and 25 tpy of any combination of HAPs. However, operating limitations were taken to remain a minor classification with regards to HAPs.

One of the benefits of a Title V permit is that it compiles all of the compliance obligations into a single document. Prior to Title V, if a business constructed ten pieces of permitted equipment at individual times, then that facility would have been required to have ten individual permits instead of one permit to update with new/modified equipment.

Title V made three significant changes to the way businesses comply with air quality regulations by requiring the business to hold an operating permit, submit compliance reports, and undergo enhanced enforcement provisions.

Businesses in the Title V program must submit periodic compliance and monitoring reports to the EPA, to show which regulations have been met and which have not. The reports also tell the agency if a facility has been collecting the data required to demonstrate compliance. An official responsible for the business must certify under perjury of law whether or not a facility is in compliance. Misinformation or noncompliance can lead to legal action if the business has ongoing compliance issues. Reporting also greatly enhances the ability of federal and state agencies to assess a compliance situation for a Title V business and take enforcement action, if one is needed.

EPA has determined Kentucky has acceptable measures in place to operate a Title V permit program and has delegate authority to the State’s Energy and Environment Cabinet, Division for Air Quality. Therefore, it is primarily the State which issues the permit; conducts inspections; reviews recordkeeping, monitoring, and reports; and initiates enforcement actions. For more information on the Title V program, please review the Educational Resources page.


Common Title V Definitions

Actual Emissions

The actual controlled emissions rate of a pollutant from a source calculated using the actual operating hours, production rates, and types of materials processed, stored, or combusted during the selected time period.


Allowable Emissions

The controlled emissions rate that represents a limit on the emissions that can occur from a source. This limit may be based on a federal, state, or local regulatory emission limit.


Continuous Emissions Monitoring (CEM)

A monitoring effort that “continuously” measures (i.e., measures with very short averaging times) and records emissions. In addition to measuring

and recording actual emissions during the time of monitor operation, CEM data can be used to estimate emissions for different operating periods and longer averaging times.


Cylinder Gas Audit (CGA)

A compliance demonstration which measures the performance of a continuous emission monitor (CEM) located in the release point (e.g., stack exhaust) of the source (e.g., boiler). The audit test is a quality assurance performance test used to validate the data collected with a CEM. If the CEM reports a concentration within an allowable percentage of the concentration found using the reference gases, then the CEM passes the audit.


Criteria Pollutants

A list of 6 common pollutants listed in the Clean Air Act for which National Ambient Air Quality Standards have been established to maintain or prevent deterioration of air quality. Ambient Standards limit the concentration of a given pollutant in the ambient air. Ambient

standards are not emissions limitations on sources, but usually result in such limits being placed on source operation as part of a control strategy to achieve or maintain an ambient standard.



Pollutant discharged into the atmosphere either as fugitive (e.g., stockpile) or non-fugitive (e.g., boiler stack). Emissions are considered non-fugitive if emitted from a source where an enclosure, collection system, ducting system, and/or stack (with or without an emission control device) is in place.


Emission Factors

A ratio that relates emissions of a pollutant to an activity level at a plant that can be easily measured, such as an amount of material processed, or an amount of fuel used. Given an emission factor and a known activity level, a simple multiplication yields an estimate of

the emissions. Emission factors are developed from separate facilities within an industry category, so they represent typical values for an industry, but do not necessarily represent a specific source. Published emission factors are available for numerous sources but are also determined from specific stack testing requirements. Use of an emission factor derived from a regulatory source stack test is required instead of a developed industrial category emission factor.


Emission Standards

A general type of standard that limit the mass of a pollutant that may be emitted by a source. The most straightforward emissions standard is a simple limitation on mass of pollutant per unit time (e.g., pounds of pollutant per hour).


Insignificant Activity

  • A source with potential to emit (PTE) equal to or less than 1,000 pounds per year of combined HAPs or five tons per year of any nonhazardous regulated air pollutant
  • The source cannot involve the incineration of medical waste
  • The source cannot be subject to a federally enforceable requirement, other than generally applicable requirements
  • For non-major sources, the emissions from all Insignificant Activities, when added with the source’s other emissions, cannot cause the source to equal or exceed a major source threshold, or an emission limit contained in the permit to avoid major source status under Title V of the Act, or New Source Review under Title I of the Act.


Hazardous Air Pollutant (also known as toxic air pollutants or air toxics)

A list of 187 pollutants listed in the Clean Air Act known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental effects. The list of HAPs includes relatively common pollutants such as formaldehyde,

chlorine, methanol, and asbestos, as well as numerous less-common substances.


Major/Title V Permits

Title V (pronounced “Title Five”) permits are required when all combined sources:

  • Emit more than 100 ton per year of any non-hazardous regulated air pollutant
  • Emit more than 10 tons per year of any single hazardous air pollutant (HAP) or more than 25 ton per year of all HAPs combined


Maximum Achievable Control Technology (MACT) Standards

Emission standard regulations that limit emissions of hazardous air pollutants based on risk to public health and emissions control technology. The regulations are source category specific and are technology-based standards requiring the use of maximum achievable control technology for specific categories (e.g., boilers and generators). The MACT standards are based on emissions levels that are already being achieved by the controlled and low-emitting sources in an industry.


National Emissions Standards for Hazardous Air Pollutants (NESHAP)

Emission standard regulations that limit emissions of hazardous air pollutants based on risk to public health. The regulations are pollutant specific and were established for asbestos, benzene, beryllium, coke oven emissions, inorganic arsenic, mercury, radionuclides, and vinyl chloride. However, the common usage of NESHAP actually refers to two different sets of standards one which includes risk-based standards and another that includes source category-specific. Therefore, the source specific category MACT regulations are also designated as NESHAP standards.


New Source Performance Standards (NSPS)

Emission standard regulations that require emissions of a regulated air pollutant including criteria, hazardous, and other pollutant emissions from a new source to be less than an older source. A new source could actually be an existing source that was modified or reconstructed to the point of being considered as new. The regulations technology-based and limited to source or industry categories deemed by EPA to significantly contribute to air pollution.


Potential to Emit

The potential emissions rate of a pollutant from a source calculated using the maximum design capacity. Potential emissions are a function of the source's physical size and operational capabilities.


Relative Accuracy Test Audit (RATA)

A compliance demonstration which measures the performance of a continuous emission monitor (CEM) located in the release point (e.g., stack exhaust) of the source (e.g., boiler). The audit test is a quality assurance performance test used to validate the data collected with a CEM. If the CEM reports a concentration within an allowable percentage of the concentration found using the reference method, then the CEM passes the audit.



An apparatus, building, operation, road, or other entity or series of entities that emits or may emit an air contaminant into the outdoor atmosphere.


Stack or Performance Test

A compliance demonstration which measures the amount of a specific pollutant or pollutants being emitted through release point (e.g., stack exhaust) of the source (e.g., boiler). A stack test may be used to demonstrate initial or ongoing compliance with federal and state regulations.