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Diesel Emissions Quantifier (DEQ)

Logging in to the DEQ allows you to save and retrieve information for review and/or revision.

More Information

On May 2, 2022, DEQ version 9.1 was released. For more information, see the Release Notes (PDF) (8 pp, 238 K).

A User Guide is now available for the DEQ:
User Guide for the Diesel Emissions Quantifier (DEQ) (PDF) (21 pp, 825 K)

DEQ Helpline: DEQhelp@epa.gov

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.

Information about Projects Saved Prior to Version 9.0
Updates to the emission factors used in the DEQ may result in different results than calculated previously.
  1. If you saved Tier 4 nonroad engines or replacements prior to version 9.0, you should be aware of the following:
    • The DEQ now asks for additional information about your Tier 4 engine's after-treatment configuration.
    • Editing your project to provide this information will allow the DEQ to more accurately reflect your emissions profile.
  2. For both onroad vehicles and projects involving Tier 4 non-road engines,
    • The baseline emissions for your project may be different than what was calculated using the previous factors.
    • For engine or vehicle replacements, the percent reductions saved with your project were calculated based on the previous factors.
    • Editing your replacement upgrade (by either adding the additional Tier 4 information or altering the new engine model year selection) will update the reduction calculations to reflect the new emissions factors.

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