Air Permits_Content Page_Air Permits Glossary

Air Permits Glossary

This glossary provides plain English, nontechnical definitions of terms frequently used in the DNR's Air Management Program related to air permits. Please refer to the Wisconsin Administrative Code [exit DNR] and Code of Federal Register [exit DNR] for the legal definitions of specific terms.

A | B | C | E | F | G | H | L | M | N | O | P | R | S | T | V

A
Acid Rain
Air pollution produced when sulfur oxides (SOx) and nitrogen oxides (NOx) combine with moisture in the air and fall to the Earth as acidic rain, snow, fog or mist. The main sources of these pollutants are combustion of fossil fuels in motor vehicles, industrial boilers and power-generating plants.
Air Reporting System (ARS)
A web-based software system that allows facilities to report annual air emissions.
Air Quality Monitor
Equipment that detects select pollutants in the air such as particulate matter, ozone, carbon monoxide and sulfur dioxide. Some air quality monitors can also be capable of measuring metrological data such as temperature and humidity.
Ambient Air
Refers to the portion of the atmosphere external to buildings and to which the public has access.
Attainment Area
A geographic area that meets the primary or secondary National Ambient Air Quality Standards (NAAQS).
 
B
Best Available Control Technology (BACT)
An emission limitation for a pollutant, determined by the DNR, based on the maximum reduction achievable taking into account energy, economic and environmental impacts and other costs related to the source.
Biogenic
When related to air pollution, refers to pollutants being produced by biological processes of living organisms.
 
C
Chlorofluorocarbons (CFCs)
Chemicals that were used in industry for refrigeration and air conditioning. When released into the air, they rise into the upper atmosphere and reduce the protective ozone layer.
Carbon Dioxide Equivalent (CO2e)
The amount (usually in metric tons) of a greenhouse gas that would have the same global warming potential as one metric ton of carbon dioxide.
Clean Air Act
The first modern environmental law enacted by the United States Congress in 1963. The Clean Air Act of 1970, reviewed and amended by Congress in 1975, 1977 and 1990, has formed the basis of the current federal air pollution control program.
Concentrated Animal Feeding Operation (CAFO)
Livestock operations where the animals are confined for at least 45 days in a 12-month period and do not have access to grass or other vegetation during the normal growing season. In Wisconsin, a CAFO generally refers to a livestock operation with 1,000 animal units, with animal units based on the weight of the animals. Also referred to as AFOs.
Continuous Emissions Monitoring System (CEMS)
A comprehensive set of equipment used to determine the concentration or emission rate of gaseous pollutants or particulate matter in industrial processes.
Control Technology
Equipment used to destroy or remove air contaminants prior to release into the ambient air.
Criteria Air Pollutants
The Clean Air Act requires the U.S. EPA to set National Ambient Air Quality Standards (NAAQS) for six commonly found air pollutants known as criteria air pollutants. Criteria Pollutants include ozone (O3), particulate matter (PM), sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2) and lead (Pb).
 
E
Emissions
A release of pollutants into the air from a source.
Emission Unit
Any part of a stationary source which emits, or is capable of emitting, any air contaminant.
EPA Class Codes
The EPA and DNR use class codes to establish compliance and enforcement priorities. The DNR assigns codes based on a facility’s potential to emit. The DNR annual emissions billing rates are based on the class code assigned to a source.
Code Description
A Major source
SM80 Synthetic minor, PTE > 80% of the major source threshold
SM Synthetic minor, PTE < 80% of the major source threshold
B Natural minor
 
F
Facility
An establishment - residential, commercial, institutional or industrial - which emits or causes emissions of air contaminants.
Federally Enforceable State Operation Permit (FESOP)
Also called a synthetic minor permit or non-part 70 permit. A type of operation permit that sets enforceable emission limitations on a facility that would otherwise require a federal operation permit.
Federal Operation Permit (FOP)
Also referred to as part 70 permit, title V permit or major source permit.
Fugitive Emissions
Emissions released from any point other than a flue or stack.
 
G
Global Warming Potential (GWP)
An index used to compare the heat-trapping ability of different greenhouse gases to that of carbon dioxide. GWP is used to calculate the carbon dioxide equivalent, CO2e, of greenhouse gas emissions from a source.
General Operation Permit (GOP)
A type of permit issued to facilities in a specific industry group with similar applicable requirements.
Greenhouse Gases (GHG)
Gases that trap heat in the atmosphere. GHGs include carbon dioxide (CO2), nitrous oxide (NOX), methane (CH4), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafloride (SF6).
 
H
Hazardous Air Contaminant
Any air contaminant for which no ambient air quality standard is set and which the DNR determines may cause or significantly contribute to an increase in mortality or an increase in serious illness or may pose a significant threat to human health or the environment. Hazardous air contaminants are regulated in ch. NR 445, Wis. Adm. Code.
Hazardous Air Pollutant
Also known as toxic air pollutants or air toxics, these pollutants are known or suspected to cause cancer or other serious health effects, such as reproductive effects, birth defects or adverse environmental effects.
 
L
Lowest Achievable Emission Rate (LAER)
The lowest pollution control limit that is technically achievable in practice for a particular industry or process. These stringent measures are for controlling air emissions from major sources and major modifications in nonattainment areas.
Liquefied Natural Gas (LNG)
Natural gas that has been cooled to a liquid state at -260° Fahrenheit for shipping and/or storage. LNG occupies a volume approximately 600 times smaller than natural gas in its gaseous state.
 
M
Major Source
  • In attainment areas for new source review, a major source is a facility or stationary source which is able to emit 250 tons per year (tpy) or more of any criteria air pollutant.
  • In attainment areas, for existing sources requiring an operation permit, a major source is a facility or stationary source that is able to emit 100 tpy or more of any criteria air pollutant or which is able to emit 10 tpy or more of any individual federal hazardous air pollutant, or which is able to emit 25 tpy or more of combined federal hazardous air pollutants.
  • In nonattainment areas, whether for new or existing sources, a major source may be defined using lower emissions thresholds than would be applied in attainment areas depending on the nonattainment designation level of the area.
Maximum Achievable Control Technology (MACT)
The level of control being achieved by the best-performing sources within an industry source category for federally regulated hazardous air pollutants. MACT is established by the EPA and applies to new and existing sources.
Maximum Theoretical Emissions (MTE)
Maximum theoretical emissions refer to the quantity of pollutant that could theoretically be emitted by an emissions unit without any control. It represents the upper limit of emissions if no pollution control measures are in place.
Metric Ton
Also tonne, a unit of weight equal to 1000 kilograms or 2,204.6 pounds.
Micron
A unit of length in the metric system where one micron equals one-millionth of a meter. To protect public health, air quality regulations refer to various sizes of particle pollution using this measure. For comparison, the average human hair is 50-70 microns in diameter, whereas fine particles are 2.5 microns or less.
Minor Source
A facility with the potential to emit air pollutants below the levels that define a major source.
Mobile Source
A source that releases pollution while moving. These consist of on-road sources such as cars, trucks and buses, and nonroad sources such as trains, planes and boats.
 
N
National Ambient Air Quality Standards (NAAQS)
A level of air quality set by the EPA intended to protect human health and public welfare. Standards have been set for six "criteria" pollutants: carbon monoxide, lead, nitrogen dioxide, particulate matter, ozone and sulfur oxides.
National Emission Standards for Hazardous Air Pollutants (NESHAP)
Stationary source standards for hazardous air pollutants.
New Source Performance Standards (NSPS)
Emissions standards for new or modified sources in source categories that contribute significantly to air pollution that endangers public health or welfare. These standards reflect the degree of emission limitation achievable through the best technology or system of emission reduction that is adequately available as determined by the EPA.
New Source Review (NSR)
A pre-construction permit program designed to maintain air quality when facilities add or change sources of air pollution. Issued to a source for new construction, reconstruction or modification of a source. A permit issued under NSR may also be referred to as a construction permit.
Nonattainment Area
Any area that has been designated by the EPA as not meeting the primary or secondary National Ambient Air Quality Standards.
 
O
Original Permit
Term used to describe either the first facility-wide operation permit issued to a facility or the first construction permit issued to a given project.
Ozone
A highly reactive gas made of three oxygen atoms. Naturally occurring ozone is found in Earth’s upper atmosphere. This ozone, also known as stratospheric ozone, reduces the amount of harmful UV radiation reaching the Earth’s surface. Tropospheric, or ground-level ozone, is what people breathe. It is formed primarily from photochemical reactions between volatile organic compounds (VOC) and nitrogen oxides (NOx) and is harmful to human health.
Ozone Precursor
Any gas in the atmosphere that reacts to form ozone. Nitrogen oxide compounds (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO) are the most common.
 
P
Particulate Matter
Solid or liquid particles suspended in the air, including PM2.5 (inhalable particles with diameters 2.5 micrometers or smaller) and PM10 (inhalable particles with diameters 10 micrometers or smaller). Particle pollution may affect sensitive groups, such as children, the elderly and people with respiratory diseases, as smaller particles can penetrate more deeply into the lungs and bloodstream.
Predictive Emission Monitoring System (PEMS)
A system that uses process or other operating parameter measurements to determine a gas concentration or emission rate of a pollutant. A PEMS is an alternative approach to a CEMS.
Permit
A legal document required by the Clean Air Act for regulated sources of air pollution. Permits are required for both the operation of existing plants (operating permit) and for the construction of new plants or modifications to existing plants (construction permit).
Per-and Polyfluoroalkyl Substances (PFAS)
A group of human-made chemicals used for decades in numerous products, including non-stick cookware, fast food wrappers, stain-resistant sprays and certain types of firefighting foam. These contaminants have made their way into the environment through accidental spills of PFAS-containing materials, discharges of PFAS-containing wastewater to treatment plants and certain types of firefighting foams. PFAS do not break down in the environment and have been discovered at concentrations of concern in groundwater, surface water and drinking water. These chemicals are known to accumulate in the human body, posing several risks to human health, including certain cancers, liver damage and decreased fertility.
Potential To Emit (PTE)
The maximum capacity of a source to emit an air pollutant under its physical and operational design.
Public Comment Period
The time allotted for the public to submit comments on draft permit materials before the DNR makes a final permit decision.
Public Hearing
Formal public proceeding held to receive comments on draft permit materials.
Public Notice
Announcement that the technical analysis, known as the preliminary determination, draft permit materials and permit application are available for the public to view. The posting of a public notice starts the public comment period.
Prevention of Significant Deterioration (PSD)
NSR regulations that apply to new major sources or major modifications at existing major sources for pollutants where the source is located in an attainment or unclassifiable area with the NAAQS.
Prevention of Significant Deterioration (PSD) Increment
The maximum allowable increase in a criteria air pollutant concentration allowed to occur above a baseline concentration. The baseline concentration is defined for each criteria pollutant and, in general, is the ambient concentration at the time that the first complete PSD permit application affecting the area is submitted (U.S. EPA, 1990 Clean Air Act Amendments).
 
R
Reasonably Available Control Technology (RACT)
Control technology that provides the lowest emission rate a source is capable of achieving and is reasonably available, both in cost and technical feasibility, to most sources within an industry sector.
Renewal
Each major source operation permit will need to be renewed every five years. Renewal applications can extend the permit until the DNR issues a renewed permit. A renewed operation permit is valid for five years. Minor and synthetic minor operation permits do not have an expiration date and therefore are not required to be renewed, although the DNR may require, or the facility may request, an expiration date.
Revisions
Changes to a permit that do not meet the definition of construction, reconstruction or modification. Construction permit revisions can include changes that are considered exempt modifications. Revisions retain the same expiration date as the permit they are revising.
Registration Construction Permit (RCP)
A type of general construction permit issued to the group of sources with low actual or potential emissions. There are multiple RCPs available at different ranges of emissions thresholds.
Registration Operation Permit (ROP)
A type of general operation permit issued to the group of sources with low actual or potential emissions. There are multiple ROPs available at different ranges of emissions thresholds.
ROG
An acronym for reactive organic gas. View definition of volatile organic compounds. The EPA formerly defined the regulated organic compounds in outdoor air as reactive organic gases (ROG) to clarify its meaning as being limited to reactive chemicals. The EPA later changed that terminology to volatile organic compounds (VOC); however, references to ROG remain in older state and federal rules. For the purposes of state air pollution regulations, ROGs can be considered equivalent to VOCs.
 
S
State Operation Permit (SOP)
Also called natural minor permit or non-part 70 permit.
Stack
Any device or opening designed or used to emit air contaminants to the surrounding air.
State Implementation Plan (SIP)
A detailed description of the programs a state uses to carry out its responsibilities under the Clean Air Act.
Stationary Source
Air pollution sources that emit or may emit from a fixed location.
Synthetic Minor
A source with maximum theoretical emissions above major source levels that accepts permit limitations to restrict potential to emit below those thresholds in order to be issued a minor source permit. May also be called FESOP. Synthetic minor sources can be categorized as either SM or SM80. An SM80 source has emissions restricted at or above 80% of the major source levels, whereas SM source emissions are restricted below 80% of the major source levels.
 
T
Title V
A portion of the 1990 Clean Air Act Amendments that requires all major sources and some minor sources of air pollution to obtain an operating permit. Title V operating permits, also called Part 70 permits, may apply to minor sources if the source is subject to certain federal air pollution regulations. May also be called a Federal Operation Permit (FOP), a major source or a Part 70 source.
Tons Per Year (TPY)
This is the typical measure used to describe emissions from a source.
 
V
Volatile Organic Compounds (VOCs)
An organic compound which reacts with other chemicals or surfaces that it contacts when exposed to light. Examples include gasoline, benzene and toluene.

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