Stack Emission Rate and Potential to Emit

Actual emissions are what gets reported annually and what fees are based on. Potential to emit is the maximum capacity to emit, computed at 8,760 hours a year at full design capacity regardless of what the source actually runs -- and it is potential, not actual, that decides whether a source needs a major source permit. The 8,760 hours is what surprises everyone. A source running one shift a day, five days a week, still has a potential computed as though it ran every hour of the year, because it COULD absent an enforceable restriction. A boiler used only for winter heating has a potential based on year-round continuous firing, and a generator used for four hours of testing a month has one based on running continuously. The way out is a synthetic minor limit, and understanding it is the practical value of the concept: if the source accepts a federally enforceable permit condition limiting its hours, its throughput or its fuel, potential is recomputed against that limit, and a source that would be major at 8,760 hours becomes minor at a permitted fraction of it. The hours that would achieve that are reported here. The trade is real -- the limit is enforceable, it carries recordkeeping and reporting obligations, and exceeding it is a violation rather than a busy month. Control equipment counts only when its operation is federally enforceable, which is why that is a separate input rather than a percentage applied automatically. A baghouse that is installed but not required by any permit condition does not reduce potential to emit, because nothing obliges the source to run it. This is a screening calculation on an ENTERED hourly rate, which itself comes from an emission factor, a stack test, or a manufacturer's data and carries all of that uncertainty. It does not select the emission factor, apply the many source-category-specific rules for what counts toward potential, address fugitive emissions and which categories must include them, aggregate emission units into a single source, or determine applicability of any permitting program. The permit, the applicable subpart, the reviewing authority, and a qualified air quality professional govern.

actual emissions = rate x actual hours / 2,000 lb per ton; potential to emit = the same rate x 8,760 hours / 2,000, at maximum design capacity; a permitted hours limit substitutes for the 8,760, and the hours that put potential exactly at the threshold is that relation inverted.

Potential to emit as EPA's permitting programs define it -- the maximum capacity to emit at 8,760 hours a year at full design capacity, with control equipment and operational limits counted only where they are FEDERALLY ENFORCEABLE. The hourly rate is ENTERED from an emission factor, a stack test or manufacturer data. A screening calculation: it does not select the emission factor, apply source-category-specific rules for what counts, address fugitive emissions, aggregate emission units, or determine applicability of any permitting program.

One rate times one number of hours; no emission factor table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: hourly_rate_lb_h, actual_hours_per_year, permitted_hours_per_year, major_threshold_tpy, control_efficiency_pct, control_enforceable, actual_tpy, pte_tpy, pte_ratio, hours_for_minor

• The hourly rate is entered it comes from an emission factor, a stack test or manufacturer data and carries that uncertaintythe source's own test data
• Control must be enforceable installed equipment no permit requires does not reduce potentialthe permit
• Not an applicability determination source-category rules, fugitives and aggregation are outside thisthe reviewing authority