Skip to main navigation Skip to main content

Potential to Emit PTE

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Understanding and Calculating PTE for Air Permit Applications

What is Potential to Emit?

Put simply, a facility's “potential to emit" (PTE) is the highest theoretical amount of pollution the facility could release into the air during a year's time, based on its designed capacity.

PTE is a key part of getting an air permit. It helps businesses explain their possible emissions to regulators, and it helps regulators decide what rules apply and whether the facility can meet them.

Permits are based on this “worst-case" estimate so that facilities have flexibility to operate without constantly needing to update their permits.

In summary, PTE is a way to measure and communicate how much air pollution a facility could produce.

All calculations, including proposed limitations/bottlenecks, will be approved or denied by the Kentucky Division for Air Quality (DAQ) Permit Review Branch before an Air Permit is issued.​

​How is PTE calculated?

PTE is calculated using the formula:

Potential Pollutant Emissions​ = 

(Maximum ​Hourly Capacity) x (Potential Operating Hours) x (Emission Factor) x (Conversion Factor)

​The following steps will guide you through filling out this equation.​

PTE will need to be calculated for each pollutant at each emission point at your facility. Individual PTEs will then be added together to get a facility-wide PTE. That facility-wide PTE is what the facility will use to determine what permit, if any, is required.​​

An emission point is the specific location where air contaminants are released from a stationary source. Emission points can be located within a building or outside. Stacks and vents are often the first things that come to mind, but emissions can also come directly from the manufacturing process itself. It is important to remember that air emissions are not always visible.


Air emission points can be identified by conducting a facility assessment, which involves walking through the facility while following each operation from beginning to end.​ Emissions from trivial activities​ are not required to be included on permits or permit applications and are not considered when determining source status or other applicability determinations.

​

​Each potential emissions point, including stationary items that burn fuels and/or generate dust, vapor, or odors, must be recorded. 

  • ​Create a layout of your facility
  • Number each emission point
    • ​​Each identifier should be unique; numbers should not be repeated
  • Gather information regarding equipment specifications
    • Including make, model, and rated capacity
  • Record any control devices that are connected to operations
    • Control devices are additional systems that reduce the release of a pollutant into the air
  • Include locations where fug​itive dust is released
    • Frequently includes haul roads and other places of transport

Common ​Emis​sion Sources​​

  • Boilers
  • Spray coating
  • Cleanup solvents
  • Welding
  • Fuel-powered generators​​​
  • Engines
  • Roadways/haul roads
  • Kilns
  • Wood and metal-cutting equipment​ ​

​​​ Often-Overloo​ked Emission Sources

  • Natural gas/diesel compressors
  • Abrasive blasting
  • Aerosol cans
  • Storage silos and stockpiles
  • Conveyors
  • Water heaters
  • Adhesives
  • Crushers and screens​​
  • Truck loadouts​​​
    ​​
    ​​​​

Maximum hourly capacity is the maximum amount of material a piece of equipment can process, burn, store, or produce in one hour,​ under its physical and operational design. Maximum hourly capacity can also be called maximum throughput, hourly capacity, rate, or a combination of these terms.

  • The maximum capacity should be determined by the manufacturer's specifications, if available. For example, spray guns and combustion units generally have a rated capacity.
  • If the maximum design capacity is unknown, use the highest recorded usage rates as a starting point. These figures must be increased to represent the equipment’s full physical and operational potential.​

​

Determine the maximum hourly capacity for each emission point (found in Step 1) using the specific units associated with its source classification code (SCC). You can find these process-specific reference units via the DAQ's approved SCC list​. For final PTE calculations, ensure all capacities are expressed as SCC units/hour.​

A facility's "potential operating hours" are the total time an emission point is capable of operating, regardless of actual operating hours. In most cases, this is assumed to be continuous operation -- 24 hours a day, 7 days a week, or 8,760 hours per year.


Bottleneck Considerations

Potential operating hours may be less than 8,760 hours per year if a bottleneck occurs within a facility's proposed operation. In air permitting, a bottleneck refers to process limitations or extenuating circumstances that prevent a process from running 24/7. If you believe this may apply to your facility, it is advised that you discuss it with the DAQ Permit Review Branch before submitting your application.​​

What is an emission factor?

An emission factor is a numerical value that estimates how much pollution is released during a specific activity. It is usually written as pounds of pollution per SCC unit (lbs/SCC unit). It is important that the SCC units used in this step match the units identified in Step 3.

For example, an emission factor for wood sawing may be expressed as 6 pounds of particulate matter emitted per every ton of wood processed (6 lbs/ton).


Identify all pollutants for each emission point.

For every emission point found in Step 1, you must identify all potential pollutants released. Keep in mind that a single process can have multiple pollutants; different pollutants may have different emission factors (for example, a boiler has different emission factors for Nitrogen Oxides than it does for Particulate Matter).

In your air permit application, it is important to reference the source for all emission factors for the DAQ to review.


​​How are emission factors identified?
AP-42
​The EPA has developed emission factor ratings for many common industrial processes. AP-42 is a compilation of 15 chapters and appendices of air pollutant emission factors. It is available on the EPA’s​ AP-42 webpage​. Each chapter has several subsections to cover sources or industries within the chapter. In addition to the emission factors, AP-42 provides descriptions of the processes.

EPA WebFIRE​
The EPA's We​bFIRE, or Factor Information Retrieval, is a web-based search engine rather than a detailed description of sources. There are two options for searching. One is a simple search based on keyword or source classification code (SCC). If the simple search returns too many results, a detailed search may be performed.

Stack Testing/Source Sampling

​​Another way to determine emission factors is the test data method. This method can provide the most accurate estimates of emissions. Unfortunately, the data needed are often expensive to obtain, particularly for businesses that emit a variety of pollutants or have a lot of fugitive emissions. Useful test data are easier to obtain when emissions come primarily from a point source, such as a smokestack. It may be necessary to collect test data over a period of time and from multiple production areas to gain a reliable measure of average emissions. Only experienced stack testers should measure emission samples and estimate total emissions.​​​​​​​ More information about stack testing can be found on the DAQ's "So​urce Sampling and Testing" webpage​.​​​


​Manufacturer Data
Equipment-specific emission factors can often be obtained from equipment vendors, especially through emission performatnce guarantees or from actual test data of similar equipment.

Material/Technical Data Sheets
Emission factors can be based on a percent-by-weight basis, as pollutant components are listed in a safety data sheet (SDS) or technical data sheet (TDS). This is the method most often used for wet-coat operations.

Software
There is software developed for certain operations. Many of these programs can be found on the EPA's "Emission Estimation Tools" webpage​. For example, there is software developed for tank emissions, landfill gases, and glycol dehydration processes. These programs generate emission data from a series of simple input variables since the calculations can be quite complex.
​

​To calculate PTE, ensure all variables use compatible units so they "cancel out" into the final units of tons per year (tpy). Use the following formula for each pollutant under each emission point:Maximum hourly capacity times potential operating hours times emission factor times a conversion factor

PTE Calculation Process​

  1. ​​Multiply the Maximum Hourly Capacity by the annual Potential Operating Hours (8,760) and the Emission Factor for the pollutant you are calculating PTE for.
  2. Convert the result to tons of pollutant per year (tpy) by dividing by 2,000. 
  3. Complete the PTE calculation for each pollutant at each emission point in your facility.
  4. Quantify the Hazardous Air Pollutants (HAPs) by summing the total of each individual HAP, as well as total combined HAPs.
  5. Quantify the total of each Regulated Air Pollutant (RAP).
  6. Compare these cumulative totals of HAPs and RAPs against the DAQ’s permitting thresholds.


Common PTE mistakes to avoid:

  • Missing data (i.e., excluding the complete list of potential pollutants for each emission point)
  • Incorrect use of emission factors
  • Lack of justification for bottlenecks
  • Mathematical errors or improper use of unit conversions​​

Air pollution controls manage air quality by capturing, neutralizing, or removing particulate matter or gases from emission points before they are released into the atmosphere. Below are examples of common control methods for particulate matter and gaseous pollutants.


Particulate Matter

  • Cyclones
  • Baghouses
  • Fabric filters
  • Scrubbers/wet collectors
  • Wet suppression

Gaseous Pollutants

  • Condensers
  • Absorbers
  • Combustion
  • Adsorbers
  • Oxidizers


Inherent Controls

A facility's total potential to emit (PTE) and its resulting air permit type are typically based on calculated emissions before any pollution controls are factored in (uncontrolled PTE calculations). However, it is beneficial to identify if your equipment utilizes inherent or essential air pollution controls. Examples include controls that are essential for final product recovery or instances where the equipment cannot physically operate while the control is shut off.​

If these controls meet the EPA's inherent criteria, you may request that the DAQ consider the controlled potential emissions for the applicable emission point(s). Accounting for inherent air pollution controls allows you to calculate annual maximum potential emissions after the control device, which may qualify the source for a lower permit threshold.

 

Please note that the DAQ makes the final determination on whether a control qualifies as inherent for PTE calculation purposes.​​​​​​

Need help calculating your facility's PTE?

Check out ECAP's "Small Business Services" webpage​ to see if you qualify for detailed help from our team. If your facility does not qualify as a small business, the Kentucky Pollution Prevention Center (KPPC) maintains a consultant directory of companies that provide a variety of environmental management services.

​​​Disclaimer

Information on this page does not supersede any guidance given by the Kentucky Division for Air Quality (DAQ). Questions or requests for assistance should be directed to the DAQ​ P​ermit Review Branch or the Environmental Compliance Assistance Program (ECAP) team.​​

​​​Contact the ECAP team ​at envhelp@ky.gov​ or (502) 782-6189.​

Kentucky Energy and Environment Cabinet
300 Sower Blvd
Frankfort, KY 40601    

Phone Directory
Contact Us
Civil Rights/Derecho Civiles

The Kentucky Energy and Environment Cabinet does not discriminate against any person on the basis of race, color, national origin, religion, age, disability or sex. This policy protects the rights of Cabinet employees, service applicants and customers. Vendors, agencies and organizations providing services to the Cabinet or its recipients of federally-aided programs also must comply with this policy.

© 2022 Commonwealth of Kentucky. All rights reserved.Kentucky.gov