General Information for Emission Inventories

The Basics of Estimating Air Emissions
Concise document discussing in very general terms how emissions are estimated.

Instructions For Air Pollutant Point Source Emission Inventory (Revised January 2014)
These are the instructions for completing the paper inventory forms, whether Title V or others. They contain general instructions, definitions, form-by-form instructions and other emission estimation guidance. Any subsequent necessary revisions and updates will also be posted here. Please contact your regional emission inventory contact if you have questions and/or comments. Thank you in advance for such feedback.

AERO User Manual
This link accesses the user manual for NC's Air Emissions Online (AERO) reporting system.

Emission Estimation for Air Permits & Emission Inventories
It is often necessary to estimate emissions emitted into the air from various facilities, for various pollutants (criteria, hazardous and/or toxic). Such estimates are needed to:

  • to determine permit classification,
  • establish or confirm compliance status,
  • update emissions for the North Carolina Division of Air Quality point source emission inventory requirements and
  • other general and site-specific reasons.

Emission inventory data are used to:

  • calculate permit fees,
  • perform toxic air pollutant modeling evaluations,
  • conduct modeling for federally required criteria pollutant attainment and maintenance plans,
  • provide appropriate data to the public,
  • monitor progress and trends and
  • many other purposes.

Individual facilities are responsible for providing proper and accurate estimates of their emissions. NC DAQ is responsible for reviewing and accepting or rejecting such estimates. The DAQ offers the following insights on how these estimates are reviewed. Usually, results from continuous emission monitoring data are the preferred way to establish emissions. However, this is not often possible or practical, except for larger facilities such as electric utilities. Use of site-specific stack tests under a single or a range of representative conditions is usually the next preferable method. Material balances can also be very accurate for some limited classes of industry, such as those that use solvents that are fully evaporated, while the same concept is near meaningless in other applications. Most frequently, however, facility management and engineers use emission factors, which have varying degrees of uncertainty, but at least are consistent. The US Environmental Protection Agency (EPA) publishes (in paper copy and electronically), A Compilation of Air Pollutant Emission Factors (AP-42), and maintains an emission factor repository, retrieval and development tool, WebFire, which is constantly being updated and improved. Users are directed to the EPA's CHIEF - AP-42, WebFIRE and related web pages for further information and to download or print sections and factors for their appropriate industry.

Not all industries are addressed (either at all or adequately) in AP-42. This section on the DAQ web page is provided to provide any additional insight and consistency in cases where judgment and interpretation of data may be appropriate for facilities (point sources only) in North Carolina or for an interim situation where AP-42 or FIRE emission factors are under development, but not yet published as final.  This information will be revised as the data improve and/or additional information is available. Users are encouraged to periodically check other sources of information to assure that they are using the "best available information" at the time.