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Hazardous Air Pollutant (HAP) Emissions Inventories

IDEM’s Hazardous Air Pollutant (HAP) emissions inventory includes estimates or reported data for hazardous air pollutants for point, area, and mobile sources. These data are used to support various efforts, including the National Air Toxics Assessment (NATA), U.S. EPA risk and technology reviews, and regional and local scale air quality modeling.

IDEM's HAP emissions inventory includes pollutants from the 1990 Clean Air Act (CAA) Amendment's HAPS list.

The geographic area of IDEMs HAPs inventory is statewide. The point sources included in the HAPs inventory are coded to a certain geographic point using county, city, address, zip code, and Universal Transverse Mercator (UTM), or latitude and longitude coordinates. Area and mobile source estimates are compiled at the county level and apportioned accordingly in modeling studies.

The HAPs inventory has been evolving since its inception in the mid 1990s. Initial HAP inventories were more limited in scope due to available knowledge, information, and resources. Improvements in HAP emissions estimating techniques and available information have resulted in improved estimates today, but quality data is still lacking in many cases. Changes in criteria pollutant reporting requirements have resulted in a complete HAP inventory every three years.

HAP Emissions Reporting

Sources within the state are required to report emissions of criteria pollutants on a regular interval. IDEM asks that sources voluntarily report their HAP emissions at those times, though it is not required. If HAPs emissions data are needed for a specific purpose IDEM has the authority under 326 IAC 2-6-5 to require certain emissions data from a source to aid in completion of that specific project.

The IDEM website provides more information about the voluntary reporting of HAPs emissions data.

Source Types

Sources for which IDEM collects HAP emissions information fall into three categories:

  • Point sources are usually large, identifiable, stationary sources of emissions. (such as power plants, steel mills, and factories) Point sources are not required to report HAP emissions to IDEM. Because of this, the HAPs inventory is compiled using information in U.S. EPA’s Community Right to Know Toxics Release Inventory (TRI), data voluntarily reported to IDEM, and emissions estimates made by IDEM.
  • Area sources include sources typically too small and too numerous to be inventoried as individual point sources. Examples include consumer and commercial product uses (such as emissions for household cleaners and lawnmowers), gas stations, small surface coaters, dry cleaners, and other smaller emission sources. Efforts are made to avoid small sources being double counted in the area and point source categories.
  • Mobile sources include on-road and off-road gasoline and diesel engines, aircraft, commercial marine vessels, and railroad emissions. IDEM has estimated mobile emissions in the past, however recent estimates for mobile sources have been made by U.S. EPA. Mobile source emissions are found on U.S. EPA's TTN website.

Learn more about Hazardous Air Pollutants.

Emissions Data Sources

  • National Emissions Inventory:
    • The National Emissions Inventory (NEI) is a comprehensive and detailed estimate of air emissions of both Criteria and Hazardous air pollutants from all air emissions sources. The NEI is prepared every three years by the U.S. EPA based on emission estimates and emission model inputs provided by IDEM, and supplemented by data developed by the U.S. EPA.
  • Toxics Release Inventory (TRI):
    • TRI is U.S. EPA’s Toxics Release Inventory Program. The TRI data includes information on releases and waste management activities reported annually by certain industries. TRI also includes stack and fugitive air releases as reported by facilities for a large number of HAPS.
  • National Air Toxics Assessment (NATA):
    • 2011 NATA inventory U.S. EPA’s most recent risk modeling inventory. It is built on the 2011 NEI and includes a number of state Quality Assurance (QA) revisions.

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