Close Menu

Main Content

Air Permitting Background and Terminology

U.S. EPA, and therefore IDEM, has created multiple definitions of the certain words and phrases. In this guide, we reference the most common definition. When actually completing an application, one should check each rule for a specific definition.

Potential to Emit (PTE)

PTE is the total potential emissions of any regulated pollutant which could result from operating under a "worst case operating scenario," running twenty-four hours a day (with no pollution control equipment), 365 days a year at full capacity. Based on the equipment capacity and other factors, IDEM’s Office of Air Quality (OAQ) will estimate the PTE for your entire source, and then determine the level of permit required for an operation. Once this has been determined, the permitting process can move forward. For more information, visit the U.S. EPA Emissions Factors and Policy Applications Center page, and refer to IDEM's non-rule policy document for the Approval of Alternative Emission Factors, Air-014 (available on the IDEM Nonrule Policies page).

Definition of a source

A source is an aggregation of one or more emission units, pollution control devices and associated origins of emissions of regulated pollutants which are all related to the production of a specific product or products and are located on one piece of property, or contiguous or adjacent properties that are owned by the same person or are under common control.

Construction and Operating permits

The Clean Air Act (CAA) calls for both construction and operating permits. IDEM has decided to combine both permits for sources. IDEM's construction permit program is called New Source Review, with various categories. IDEM's operation permit program is broken down into registrations, Minor Source Operating Permits (MSOPs), Federally Enforceable State Operating Permits (FESOPs), and Title V. IDEM has several alternative operating approvals, including Permit-by-Rule and Source Specific Operating Agreements (SSOAs).

The Major and Minor Warning

U.S. EPA tends to use the term "major" for when something is subject to a given program. U.S. EPA tends to use "minor" for when something is not subject or subject to lesser requirements of a given program. Just because a source is major for one program does not mean it will or will not be major for another. The question to ask is, "Major for what?"

New Source Review (NSR)

New Source Review is the phrase used for any type of construction or modification. Categories are:

  • Minor NSR
  • Major NSR
    • Prevention of Significant Deterioration
    • Nonattainment NSR (aka: Emission Offset)

NSR means there is a new source of air emissions for which potentially applicable rules will be evaluated during review of the permit application. All NSR requires a review of applicable requirements, determination of necessary compliance determination, monitoring, recordkeeping, and reporting. Minor NSR is a project that does not trigger PSD or emission offset requirements. Minor NSR does not require any new requirement beyond what is in the existing permit. During a minor NSR review, a Permittee may voluntarily choose to take limits on their PTE to get a lower level permit. The goal of minor NSR is to ensure the Permittee knows all of their air requirements prior to construction or modification.

Major NSR serves to ensure that new major sources will not contribute to the degradation of air quality, that any large new or modified industrial source will be as clean as possible, and that advances in pollution control occur concurrently with industrial expansion. To do this, Major NSR includes all the steps of Minor NSR plus specific cases by case reviews that create new emission limits, compliance determination requirements and compliance monitoring requirements.

Prevention of Significant Deterioration

Prevention of Significant Deterioration (PSD) applies to new major PSD sources, modifications that themselves are a major PSD source at a minor PSD source, or major PSD modifications at existing major PSD sources for pollutants in attainment areas or areas that are unclassifiable under the National Ambient Air Quality Standards (NAAQS). It requires: the installation of the "Best Available Control Technology (BACT)"; an air quality analysis; an additional impacts analysis; and public involvement. Additional information is provided on the U.S. EPA New Source Review page.

Nonattainment NSR

Nonattainment NSR permits are required for new major sources or major sources making a major modification in a nonattainment area. Nonattainment NSR requires the installation of the lowest achievable emission rate (LAER) and Emission Offsets. Emission Offsets are emission reductions, generally obtained from existing sources located in the vicinity of a proposed source which must: (1) offset the emissions increase from the new source or modification; and, (2) provide a net air quality benefit. The purpose for requiring offsetting emissions decreases is to allow an area to move towards attainment of the NAAQS while still allowing some industrial growth. U.S. EPA provides information about Nonattainment NSR on its New Source Review Basic Information Web page.

Operating permits

IDEM issues operating permits that compile all applicable requirements. The greater the expected emissions at the source, the higher the level of permit approval required. A source's Potential to Emit (PTE) a regulated pollutant (or more than one regulated pollutant) is a primary factor in determining the appropriate approval or permit required for its operation. IDEM issues and enforces permits and U.S. EPA has continuing oversight over Indiana’s air permit program and enforcement program.

Operating conditions

Indiana’s air permits have five main sections: a Source Summary, which tells what kind of industry the source is engaged in and lists the equipment that is regulated by the permit; General Conditions, containing provisions that are necessary for the permit to work or are a general requirement on the Permittee; Source Operation Conditions; Facility Operating Conditions, which specifically regulate the source and require specific controls and limits on emissions; and, incorporation of federal standards.

Each facility operating section has up to four parts: Emission Limits and Standards; Compliance Determination Requirements; Compliance Monitoring Requirements; and, Record Keeping and Reporting Requirements.

State Implementation Plan (SIP)

A State Implementation Plan (SIP) is a detailed description of the programs a state will use to carry out its responsibilities under the Clean Air Act. State Implementation Plans are collections of the regulations used by a state to reduce air pollution. The Clean Air Act requires that U.S. EPA approve each State Implementation Plan. Members of the public are given opportunities to participate in review and approval of State Implementation Plans.

New Source Performance Standards (NSPS)

New Source Performance Standards (NSPS) apply to some "new "sources. The "new' is generally based on the date the specific standard came out. Performance standards are set by industry type. The New Source Performance Standards (NSPS) establish emissions limits for some new or modified sources. The federal regulations for NSPS can be found in Title 40, Chapter 1, Subchapter C, Part 60 of the Code of Federal Regulations (40 CFR 60).

National Emission Standard for Hazardous Air Pollutants (NESHAP)

NESHAPs set requirements for specific industries in limiting the release of Hazardous Air Pollutants (HAPs). The Clean Air Act requires U.S EPA to regulate emissions of toxic air pollutants from a published list of industrial sources referred to as "source categories." U.S. EPA has developed a list of source categories that must meet control technology requirements for these toxic air pollutants. The U.S. EPA is required to develop regulations (also known as rules or standards) for all industries that emit one or more of the pollutants in significant quantities. U.S. EPA has developed implementation tools (eg.including checklists and brochures) to help comply with the standards. The NESHAPs can be found in 40 CFR 61 and 40 CFR 63. Visit the Rules and Implementation Web page on U.S. EPA’s Air Toxics Web site for more information.

Public notice

IDEM publishes a notice regarding the issuance of draft permits, prior to issuing a final permit decision. The public notice seeks public comment. The public comment period is usually 30 days. Anyone can request that IDEM conduct a public hearing regarding a draft permit. IDEM will review the request and make a determination on holding a hearing. IDEM may also choose to hold a public meeting. Regardless if IDEM holds a public hearing or meeting, IDEM will accept all written comments on the permit. Where public hearings are held, the public comment period may be extended. Following the public comment period, IDEM makes the final permit determination. The final determination includes IDEM’s response to all written comments.

Regulated Pollutants

The 1970 Clean Air Act identified Criteria Air Pollutants and Hazardous Air Pollutants (HAPs), and required the U.S. EPA and states to control these pollutants. Regulations include New Source Review (NSR), New Source Performance Standards (NSPS), National Emissions Standards for Hazardous Air Pollutants (NESHAP), and State Implementation Plans (SIPS). The same pollutant may be regulated under more than one of these regulatory standards. For example, lead is both a Criteria Air Pollutant and a Hazardous Air Pollutant.

Criteria Air Pollutants

The National Ambient Air Quality Standards (NAAQS) set the allowable level of pollution in the air for the six Criteria Pollutants. Criteria Air Pollutants are pollutants or precursors for which National Ambient Air Quality Standards (NAAQS) have been established. These include: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter (also known as particle pollution), and sulfur dioxide. The U.S. EPA determines whether the air in Indiana meets the NAAQS for each criteria air pollutant. If an area meets the NAAQS, it is considered “in attainment”. If an area fails to meet the NAAQs for a criteria pollutant it is considered “nonattainment” for that pollutant. The state must develop a plan to improve air quality for that pollutant. This plan includes more stringent emission limitations for the pollutant, as well as, more stringent permitting requirements.

IDEM operates a network of air monitors across the state to monitor for levels of six criteria air pollutants in the ambient air.

Ground level ozone isn’t directly emitted. Its precursors are nitrogen oxides and volatile organic compounds. The U.S. EPA Air and Radiation: Six Common Air Pollutants page provides information about carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter and sulfur dioxide.

Hazardous Air Pollutants

Hazardous Air Pollutants are also known as HAPs, toxic air pollutants or air toxics. U.S. EPA is required to control 188 hazardous air pollutants. The 1990 Clean Air Act Amendments direct U.S. EPA to set standards for all major sources of air toxics and some area sources that are of particular concern. U.S. EPA’s Pollutants & Sources page on its Air Toxics site provides more information, including a list of toxic air pollutants that must be controlled and information about standards for sources.

"Major" sources are defined as sources that emit 10 tons per year of any of the listed toxic air pollutants, or 25 tons per year of a mixture of air toxics. These sources may release air toxics from equipment leaks, when materials are transferred from one location to another, or during discharge through emission stacks or vents.

"Area" sources consist of smaller-size facilities that release lesser quantities of toxic pollutants into the air. Area sources are defined as sources that emit less than 10 tons per year of a single air toxic, or less than 25 tons per year of a combination of air toxics.

The National Emissions Standards for Hazardous Air Pollutants (NESHAPs) set requirements for specific industries in limiting the release of Hazardous Air Pollutants (HAPs).

Permit appeals

Upon an IDEM final permit decision, any person who disagrees with an IDEM permit may seek administrative review. Petitions for Review are filed with the Indiana Office of Environmental Adjudication. Permit documents contain instructions for filing permit appeals. Visit the Office of Environmental Adjudication’s Web site for more information, including a guide to the appeals process.

News and FAQs

Top FAQs