Potential to Emit - Kentucky Energy and Environment Cabinet

Understanding and Calculating PTE for Air Permits

What is Potential to Emit?

Put simply, a facility's “potential to emit" (PTE) is the highest 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 short, 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:

(Hourly Capacity) x (Potential Operating Hours) x (Emission Factor) x (Conversion Factor) = Pollutant Emissions

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

Step 1: Identify all air emission points at your facility

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

This can be accomplished by conducting a facility assessment, which involves walking through the facility while following each operation from beginning to end.

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 limit the release of a pollutant into the air

Include locations where fugitive dust is released

Frequently includes haul roads and other places of transport

Common Sources	Often-Overlooked Sources
Boilers	Natural gas/diesel compressors
Spray coating	Abrasive blasting
Cleanup solvents	Aerosol cans
Welding	Storage silos and stockpiles
Fuel-powered generators	Conveyors
Engines	Water heaters
Roadways/haul roads	Adhesives
Kilns	Crushers and screens
Wood and metal-cutting equipment	Truck loadouts

Step 2: Determine hourly capacity for each emission point

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

Physical or operational limitations include factors such as the manufacturer's rated capacity of the equipment, air pollution control equipment, or enforceable restrictions on hours of operation. They can also include the amount of material combusted, stored, or processed.

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 hourly capacity of the process is unknown, it may be estimated by taking actual usage rates and actual hours of operation for the equipment and then adjusting them to represent potential operating scenarios.

Hourly capacities are identified using source classification code (SCC) units. These units are process-specific and can be found using the EPA's SCC search tool.

For the purposes of your final PTE calculations, units will be in SCC units/hour. Hourly capacity will need to be determined for each emission source found in Step 1.

Step 3: Determine potential operating hours

A facility's potential operating hours are the amount of time during which a source could possibly operate. This is generally 24 hours a day, 7 days a week -- 8,760 hours per year.

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.

Step 4: Determine emission factors

An emission factor is a numerical value that estimates how much pollution is released for a certain amount of work or material.

Emission factors are expressed in terms of pounds of pollution per Source Classification Code (SCC) unit -- (lbs/SCC unit). These units should be the same as those used 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).

It is important to use the correct emission factor for the specific process you’re looking at. The number should also reflect real-world conditions, including both normal operations and times when things don’t run as expected. Each emission point identified in Step 1 will have its own emission factor. For the purposes of your final PTE calculations, units will be in pounds/SCC unit.

How are emission factors identified?

AP-42 and EPA WebFIRE

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. The EPA's WebFIRE, 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

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.

Only experienced stack testers should measure emission samples and estimate total emissions.

Calculating Your PTE

When calculating PTE, it is important to ensure that all variables are using the same units so they will "cancel out" and provide the desired end units (i.e., tons per year). Emission factors and hourly capacities are identified using source classification code (SCC) units, which are process-specific units. Using the variables identified in the prior steps, a source's PTE can be calculated using the formula:

(Hourly Capacity) x (Potential Operating Hours) x (Emission Factor) x (Conversion Factor) = Pollutant Emissions

(SCC units/hour) x (hours/year) x (pounds/SCC unit) x (ton/2000 pounds) = (tons/year)

In short, you will be multiplying results from Step 2 by the results from Step 4, by 8,760. If done correctly, after incorporating the conversion factor, your calculations should come out in tons/year of Potential Air Emissions.

Issues that can complicate or make PTE calculations incorrect include:

a lack of information on emission points
knowing when to include fugitive emissions in pollutant thresholds
knowing when to include control devices to determine facility-wide pollutant thresholds
justification for physical or operational limitations
mathematical errors or improper use of unit conversions

Once the PTE calculations are completed for each process, add each pollutant to obtain the facility-wide PTE summary. In addition to noting the PTE for individual HAPs, sum the individual HAPs to develop the total HAP potential. Identify the permitting classification that is the most appropriate for the facility's activities.

Integrated Control Considerations

Permit decisions are usually based on emissions before any pollution controls are applied. However, sometimes a control device is considered essential to how a process operates. Whether a piece of equipment is seen as essential or not affects which emissions are counted and what type of permit is needed. The Division for Air Quality (DAQ) makes that determination. If you're unsure, assume the control equipment is not essential.

Some control devices aren't needed for the process to run but are used to reduce pollution. Others may be required to meet air quality standards, including as a condition of a permit, or required by federal regulations.

PTE Calculators

The National Small Business Environmental Assistance Program (SBEAP) network has compiled a webpage with tools that are designed to assist your facility in estimating its PTE from various operations.

Browse PTE resources

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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 Permit Review Branch or the Environmental Compliance Assistance Program (ECAP) team.

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

Potential to Emit PTE

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Understanding and Calculating PTE for Air Permits

What is Potential to Emit?

​How is PTE calculated?

Integrated Control Considerations

ECAP Main Page

Division for Air Quality

Source Classification Codes

PTE Calculators

​​​Disclaimer

Understanding and Calculating PTE for Air Permits

How is PTE calculated?

Disclaimer