Emissions Inventory

Industrial plant with stacks


In compliance with the Clean Air Act (CAA) Amendments and the Air Emissions Reporting Rule (40 CFR Part 51 Subpart A), the APCD conducts annual inventories of air emissions from point sources and periodic inventories of emissions from area sources, nonroad mobile sources, and onroad mobile sources.

What Is an Emissions Inventory?

An emissions inventory is a list of sources of air pollution and the amount of each pollutant emitted into the atmosphere. The inventory includes criteria air pollutants (CAPs) and hazardous air pollutants (HAPs) for sources in several categories (point, area, onroad, mobile, and nonroad mobile).

Why Are We Collecting Emissions Inventories?

In order to understand air quality in our region, we must know the sources of air pollution. Emissions inventories facilitate many activities involved in air quality policy, planning, outreach, and regulation.

State and local agencies are required to submit emission data to EPA’s National Emissions Inventory (NEI) for CAPs and HAPs for:

  • Point sources
    • annually
    • by surveying actual facilities for specific emission data
  • Area, onroad mobile, and nonroad mobile sources
    • every three years (2008, 2011, 2014, etc.)
    • by estimation and modeling

Do I Need to Submit an Emissions Inventory?

YES, if you are subject to Title V or received a letter from APCD. You will need to download emissions inventory forms, fill them out, and send them to the address given in the forms by the appropriate due date.

NO, if you did not receive a letter from APCD. Your emissions are accounted for through estimation and modeling.

NOTE: FEDOOP and Minor sources are no longer required to submit an Annual Emissions Inventory Report. However, all sources must continue to comply with record-keeping and reporting permit provisions and all other regulatory requirements.

How Are Point Source Emissions Inventories Conducted?

APCD requests information about the amount of material used or processed at certain industrial and commercial facilities known as point sources. These facilities receive a letter in the early part of the calendar year. Along with activity levels, companies submit estimated emissions. Emissions from each process are assigned to release points (stack or fugitive) at a facility so that dispersion modeling can be performed.

Emissions can be estimated several ways. Here are several examples:

  • Mass balance – Tracking inputs and outputs of materials to account for the portion that is emitted to the air. This method works well with uncontrolled use of solvents and volatiles that evaporate during use.
  • Emission factors and emission models – Ratio of emissions to production or usage rate for various processes. For example, 7.6 lb Particulate Matter/1,000,000 cubic feet natural gas burned. For more information see EPA Emission Factors AP-42.
  • Direct measurement – Stack testing and in-stack electronic monitoring provide emission amounts.

APCD reviews the submitted inventories for accuracy and thoroughness through an EPA-approved Quality Assurance Project Plan (QAPP). Several levels of internal review are conducted to ensure proper accounting of all emissions.

Point source emissions are reported through electronic data transfer to the EPA’s National Emissions Inventory by the appropriate due dates.

Area Sources

Body shop and fireplaceEmissions inventories for area sources, which include small stationary sources, are required to be reported to the EPA every three years for the NEI. Inventories are also developed for regional air quality planning work. These data are generated using EPA-approved modeling methods and reported as county totals by APCD. Reported pollutants include the six CAPs as well as a number of HAPs, including benzene, 1,3-butadiene, formaldehyde, acetaldehyde, toluene and others. These inventories are used in determining compliance with the NAAQS and for on-going policy development and community planning.

Some examples of area sources include:

  • dry cleaner plants
  • fueling stations
  • vehicle paint shops
  • occasional bonfires
  • wood-burning for heat
  • various fuel combustion processes
  • household cleaners and products
  • architectural coatings
  • industrial and commercial solvent use
  • waste-disposal activities
  • asphalt paving
  • fuel transport and delivery

Mobile Sources

Lawnmmower and trafficEmissions inventories for mobile sources are required to be reported to the EPA every three years for the NEI, and are developed for regional air quality planning work. They are generated and reported as county totals by APCD. Reported pollutants include the six CAPs as well as a number of HAPs, including benzene, 1,3-butadiene, formaldehyde, acetaldehyde, and toluene. These inventories are used in determining compliance with the NAAQS for transportation and community planning, and on-going policy development. Both onroad and nonroad mobile source emissions are reported.

Emissions inventories are calculated for the metropolitan planning area counties (Bullitt, Jefferson and Oldham counties in Kentucky, and Floyd and Clark counties in Indiana) using current EPA/FHWA – developed mobile modeling software. Local input data are fed into these models to best represent the Louisville area mobile emissions.

What Are Emissions Inventories Used for?

Emissions inventories are the basis for numerous efforts including analysis of trends, the impact of regulations on air quality, and human exposure modeling. In addition, inventories are used in local and regional emissions modeling which can help us understand current air quality, and forecast future trends in the Louisville Metro area. Quality emissions inventories:

  • lead to a more thorough consideration of certain industries or emission sources;
  • provide the foundation for the development or evaluation of control strategies;
  • aid in the evaluation of regulation effectiveness;
  • serve as a basis for emissions fee programs, permitting, and air quality assessments; and
  • support the development of new methodologies and techniques for estimating emissions (including emission factors).

Emissions inventories are an essential component used in assessing, planning for the improvement of, and protecting local air quality. You can check the local air quality where you live at http://www.epa.gov/myenvironment/.

For detailed information on uses of emissions inventories please visit EPA’s NEI website at http://www.epa.gov/ttn/chief/. National Emissions Inventory Data & Documentation can be found at http://www.epa.gov/ttn/chief/eiinformation.html


Here is a list of frequently asked questions about the emissions inventory process.

If you have questions about or need assistance with emissions inventories, please call (502) 574-6000.