Ask the Experts

Potential to Emit (PTE) is a term often found in air quality permitting and regulatory compliance discussions. The federal definition can be found in 40 CFR 52.21(b)(4), 51.165(a)(1)(iii), and 51.166(b)(4).

Is the PTE rate the accurate emission rate during normal operations?

Any rates during a facility's normal operations are typically less than the actual potential to emit (PTE) rate. PTE is the emission rate during a facility's total capacity, and most equipment is operated at less than it's maximum capability. If the equipment were operating at maximum capacity, then its actual emission equal its potential to emit.

Does the PTE rate account for maintenance downtime?

The most common method for calculating the PTE rate does not include any maintenance downtime. It assumes that the equipment is operating full-time, or 8760 hours per year.

Can the PTE rate be reduced through operating hours?

Yes, however, the operating hours reduction must be part of the original permit conditions. This type of permit condition will account for regular maintenance downtime. The hours of operation cannot be exceeded without a permit modification.


What is the largest PTE rate allowable without a permit?

The allowable rate will depend upon the applicable jurisdiction. A federal Title V permit is not required for PTE rates below 100 tons per year for an entire plant within an attainment area. In addition, if the facility's actual emissions are below 50 tpy, even if the PTE rate is greater than 100 tpy, then a Title V permit is not required.

Are there other ways to limit the PTE rate?

The PTE rate can also be limited by a New Source Performance Standard (NSPS) which is found in 40 CFR Part 60, or a National Emission Standard for Hazardous Air Pollutants (NESHAP) found int 40 CFR Parts 61 and 63 ("Guidance on Limiting Potential to Emit in New Source Permitting", USEPA Memorandum from Terrell E. Hunt and John S. Seitz, June 13, 1989).

Note: If the facility qualifies under either standards, then it must obtain a federal Title V permit.

Can a permit request with a specified emission limit, like 99 tpy, be used to avoid Title V permitting?

No. The permit must have practically enforceable conditions, such as operating hours limitations or fuel usage in order to ensure that the 99 tpy limit is actually being respected (682 F. Supp. 1133, D. Colo., Oct. 30, 1987). An exception to this requirement is if the facility operates a continuous emission monitor (CEM) that can be used to measure the emission limits


What is the PTE rate for paint spray operations?

Painting can theoretically create excessive emissions if the actual operational hours were at 8760 hours per year, which is not realistic. The PTE rate for a painting operation is limited by the permit's allowance. Unless the facility uses aerosol cans, a permit will be required.


Can the PTE rate be limited by using control equipment?

Yes, if the permit conditions require the facility to use the control equipment routinely. In addition, the removal efficiency of the control equipment must be demonstrated by a measurable quantity (i.e. pressure drop through a bag house, water flow through a scrubber, or the operating temperature log for a thermal oxidizer).


Is an equipment's design capacity the appropriate number to use to calculate its PTE rate?

Yes, the design (or name) capacity of an equipment is a valid basis for calulating the PTE rate, however, it is important to realize that this number's usage will restrict the equipment's operation to this specific capacity. Frequently, equipment (such as a boiler) can be operated for some period of time at levels that are greater than the design capacity. If this is possible, the PTE rate needs to be based upon this achievable capacity.


How is an equipment's PTE rate calculated?

Estimated emissions can be calculated through various methods. If the equipment is purchased (i.e. an engine or boiler), the vendor will be able to provide estimated hourly emission rates which can be multiplied by the permit's proposed yearly usage.

Is there another alternative in case the manufacturer cannot provide emission estimates?

The next best method for PTE rate calculations is to use EPA AP-42. It is available at their website: AP-42 provides emission factors that can be multiplied by the equipment's estimated usage, resulting in emission estimates.


What PTE rate records are necessary for compliance?

The facility must be able to prove that the equipment is operating consistently with the permit's conditions or exemptions (i.e. less than 10 tpy), which in turn implies that record keeping is mandatory. Necessary records are usually specified in the permit (unless the permit is aged), as well as their time retention.

Can the PTE rate be calculated as an average?

Most written regulations specify the PTE rate as an annual number (i.e. tons per year). Current permits include the permit limits calculated as annual averages, such as a rolling average of monthly emissions. With this, inspectors can determine the facility's compliance on a monthly basis rather than awaiting the year end. Rolling averages also provide less flexibility to the facility, as it cannot "make up" high emission rates as easily as below average emission rates.




Copyright 2007, Entech Consulting Group