Do you need an APEN or air permit?

First determine if you need an APEN, then determine if you need a permit. The steps to do this are outlined below.

What is an APEN?

An APEN is an Air Pollutant Emission Notice, and is used to:

  • Report your emissions.
  • Apply for a permit.
  • Modify an existing permit.

Your application will be rejected if it is filled out incorrectly, is missing information, missing required forms, or lacks payment for the filing fee. The Form APCD-100 and all applicable forms on that checklist are required with every application. The re-submittal will require a new filing fee. See our Application Rejection Frequently Asked Questions page for more information.


The following application types are exempted from the requirement to submit the Permit Application/Registration Checklist (Form APCD-100):

  • Air Pollutant Emission Notice (APEN) updates only (no changes to permit).
    • Renewal of 5-year APEN term.
    • Update to actual annual emissions, per AQCC Reg. 3, Part A, Section II.C.
  • APEN exempt sources.
  • Permit exempt sources.
  • Administrative permit amendments. (Including but not necessarily limited to name changes, changes in contact information, transfers of ownership, and typographical error corrections.)

You must update your APEN every five years, or if your actual emissions increased from the levels reported on a previous APEN. 

Video guide
If you're new to this process, watch this video for an introduction to emissions reporting and permit applications.

Detailed guidance
to report air emissions and apply for a permit.

Guidance at-a-glance

Steps 1-3: Determine your sources of air pollution, what pollutants are being emitted, and what federal requirements apply.

“Criteria pollutants” and “non-criteria pollutants” are regulated.

Criteria pollutants include: carbon monoxide, nitrogen oxides, sulfur dioxide, PM10, PM2.5, total suspended particulates, ozone, volatile organic compounds, lead, fluorides, sulfuric acid mist, hydrogen sulfide, total reduced sulfur, reduced sulfur compounds, and municipal waste combustor emissions.

Non-criteria pollutants are called hazardous air pollutants (HAPs) and are found in Regulation No. 3 Appendix B.

Step 4: Check if your source is exempt.

A full list of the sources that don’t need to submit an APEN is in Regulation No. 3, Part A.II.D. (APEN-exempt). If your source type is on this list, you don’t need to submit an APEN or get a permit - and you’re done here.

If your source is not on the list, your emissions still may be below the threshold for requiring an APEN. Calculate your emissions to determine if you need to submit an APEN.

Step 5:  Calculate your emissions.

Guidance for calculating your emissions.

We provide resources (including guidance, tools, and policy memos) on our website, categorized by equipment type or source type, to help you calculate your emissions.

Step 6: Determine if you need to submit an APEN based on your emissions.

You must first determine if your source is located in the ozone nonattainment area. The Denver Metro/North Front Range area (DM/NFR) is considered to be nonattainment for the National Ambient Air Quality Standards (NAAQS) for ozone. 

Sources in the 8-hour ozone nonattainment area must submit an APEN if VOC and/or NOx emissions are above their nonattainment area thresholds. The nonattainment threshold only applies to VOC and NOx; emissions for all other pollutants should be compared to the attainment threshold. Sources outside the 8-hour ozone nonattainment area should compare emissions to the attainment thresholds.  

For more information about the 8-hour ozone nonattainment area, refer to this fact sheet or look at our interactive map. If you are still unsure if your facility is in the nonattainment area, contact us.

If your emission rate is higher than APEN thresholds in the table (and your source does not qualify for an exemption based on something other than emissions), you need to submit an APEN. The uncontrolled actual emissions in a calendar year must be compared to the APEN threshold.

If your emission rate is below APEN thresholds, you don't have to submit anything to us. Continue to keep track of your emissions and revisit this page if they go above APEN thresholds.

When considering permit thresholds, all sources of emissions at the same site that are above APEN thresholds for a given pollutant must be added together and then compared to the appropriate permit threshold for the pollutant. 

APEN and Permit Reporting Thresholds

for Attainment and Nonattainment Areas

 Calendar Year Uncontrolled Actual Emissions
APEN ThresholdsPermit Thresholds1


(Volatile Organic Compounds)

2 tons1 ton5 tons2 tons



2 tons


5 tons




2 tons


5 tons



(Total Suspended Particulates)

2 tons


10 tons


CO (Carbon Monoxide)


2 tons


10 tons


SOx (Sulfur Dioxide)


2 tons


10 tons


NOx (Nitrogen Oxide)


2 tons1 ton10 tons5 tons

Other Criteria Pollutants3


2 tons


2 tons


Pb (Lead)


100 pounds


200 pounds



(Hazardous Air Pollutants)

250 pounds



1These thresholds are for equipment from the entire facility (total facility uncontrolled actual emissions from all sources above APEN thresholds for this pollutant), and not just one individual piece of equipment.

2Colorado does not have an existing nonattainment area for this pollutant and utilization of the attainment area thresholds is appropriate.

3Other criteria pollutants: fluorides, sulfuric acid mist, hydrogen sulfide, total reduced sulfur, reduced sulfur compounds, and municipal waste incinerator emissions.

Steps 7 and 8: Determine if you need an air permit.

If you do not need an air permit, complete and submit APEN forms and fees.

If you need an air permit, go to Step 9.

If your source requires an APEN, you might need a permit. Just like with APENs, a source can be exempt from permitting based on type or emissions.
If you have multiple sources at your facility, consult the complete guidance.
A full list of the sources that don’t need a permit is in Regulation No. 3, Part B.II.D. If your source type is on this list, you don’t need to get a permit. But, if your source requires an APEN, you still must submit an APEN. We have listed frequent exemptions on Common APEN or air permit exemptions.
If your source type is not listed as permit-exempt in Regulation No. 3, Part B.II.D., your emissions still may be below the threshold for requiring a permit. The permit emissions thresholds are in the table above. Note that the permit thresholds apply to your entire facility, not just the source you are reporting.
Add the emissions you calculated to the emissions from all other emissions sources at that same facility that require an APEN. If that total meets or exceeds the permit thresholds in the table above, a permit is required.

Step 9: Submit an APEN or apply for a permit.

When to submit your permit application

In Colorado, an air permit is required before you start constructing a new source or before you start modifying an existing source.