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AP-42 Emission Factor Lookup & Calculator

Browse EPA emission factors by source category with built-in annual emissions calculation

Free AP-42 emission factor reference and calculator. Select from natural gas combustion (Ch 1.4), fuel oil (Ch 1.3), diesel engines (Ch 3.3/3.4), gas turbines (Ch 3.1), and crushed stone processing (Ch 11.19). View emission factors with EPA quality ratings, then enter capacity to calculate annual emissions in tons per year. Includes full AP-42 section references for permit applications.

Pro Tip: Pay attention to the EPA quality rating letter. An A-rated factor means multiple high-quality tests from many sources. An E-rating means the factor came from a single test or engineering estimate and could easily be off by a factor of 2-5x. When your facility permit hinges on the number, site-specific testing is almost always worth the cost.

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AP-42 Emission Factor Lookup
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How It Works

  1. Select Source Category

    Choose the combustion or process source type that matches your equipment. Categories correspond to specific AP-42 chapters and sections.

  2. Review Emission Factors

    Browse the emission factor table showing each pollutant, factor value, units, EPA quality rating (A through E), and applicable notes.

  3. Enter Equipment Parameters

    Input your equipment capacity and annual operating hours, or enter annual fuel consumption directly. The calculator converts to annual emissions automatically.

  4. Use Results for Documentation

    Copy the emission factors and calculated emissions for use in permit applications, emission inventories, or compliance reports. The AP-42 section reference is provided for proper citation.

Built For

  • Consultants looking up emission factors for permit applications
  • Plant engineers estimating emissions from new or existing equipment
  • State agency staff reviewing emission inventory submissions
  • Students and researchers studying air quality engineering
  • Operations staff verifying emission calculations against published factors

Assumptions

  • Emission factors reflect uncontrolled emissions unless otherwise noted.
  • Equipment operates at steady-state conditions during the reported period.
  • Standard fuel compositions are assumed for fuel-specific factors.

Limitations

  • Coverage limited to the most commonly used AP-42 chapters (1.3, 1.4, 3.1, 3.3, 3.4, 11.19).
  • Does not include process emission factors (kilns, dryers, chemical manufacturing).
  • Sulfur-dependent factors use default fuel sulfur values that may not match your fuel.

References

  • EPA AP-42, 5th Edition, Volume I: Chapter 1.3 - Fuel Oil Combustion (September 1998)
  • EPA AP-42, 5th Edition, Volume I: Chapter 1.4 - Natural Gas Combustion (July 1998)
  • EPA AP-42, 5th Edition, Volume I: Chapter 3.1 - Stationary Gas Turbines (April 2000)
  • EPA AP-42, 5th Edition, Volume I: Chapter 3.3 - Gasoline and Diesel IC Engines (October 1996)
  • EPA AP-42, 5th Edition, Volume I: Chapter 3.4 - Large Stationary Diesel Engines (October 1996)
  • EPA AP-42, 5th Edition, Volume I: Chapter 11.19 - Crushed Stone Processing (June 2004)

Frequently Asked Questions

AP-42, Compilation of Air Pollutant Emission Factors, is the EPA's primary reference document for air pollutant emission factors. Volume I covers stationary point and area sources (combustion, industrial processes, waste disposal). It has been continuously updated since 1972 and contains emission factors for hundreds of source categories, each with EPA quality ratings from A (excellent) to E (poor).
A = Excellent: factor developed from many tests at many facilities, reviewed extensively. B = Above Average: developed from a reasonable number of tests. C = Average: developed from a small number of tests with reasonable methodology. D = Below Average: based on a small number of tests with questionable methodology. E = Poor: based on a single test, engineering judgment, or very limited data.
AP-42 factors should not be the sole basis for: compliance demonstrations at major sources (use CEMS or stack testing), health risk assessments requiring precise emission rates, or trading programs requiring verified emissions. They work well for: preliminary permit screening, emission inventory estimates for minor sources, comparing fuel or equipment options, and rough project planning.
Disclaimer: Emission factors presented here are from EPA AP-42 and represent long-term averages for the source categories shown. Actual emissions from specific equipment may vary significantly from these averages. AP-42 factors should not be used as the sole basis for compliance demonstrations or health risk assessments. Always reference the original AP-42 document for complete notes and applicability guidance.

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