EPA Revisions to Storage Tank Emission Calculation Methodologies

On November 20, 2019, the United States Environmental Protection Agency (USEPA) finalized revisions to AP-42 Chapter 7, Section 7.1 – Organic Liquid Storage Tanks, which provides approved emission estimating methodologies for storage tanks. Additional revisions were incorporated in March 2020. The methodologies include emission estimates for working and breathing (standing) losses, but not for flashing losses. The revisions include:


  • Updated meteorological data.
  • Replaced equations historically used to obtain approximate values with more accurate equations.
  • Addition of methodology for estimating losses from tank cleaning.
  • Working loss emission calculations based on changes in liquid level rather than throughput.
  • Revised the tank condition and color inputs and updated associated equations.
  • Addition of separate calculations for uninsulated, partially insulated, or fully insulated tanks.


The EPA TANKS 4.09d emissions estimation software program has now become obsolete. This program has not been supported by USEPA for several years, it is known to have errors, and it does not include the recent changes to AP-42 Chapter 7. As of April 9, 2020, the Oklahoma Department of Environmental Quality (ODEQ) has requested that applicants discontinue the use of TANKS 4.09d for all air permit application submissions.


The AP-42 Chapter 7, Section 7.1 methodology revisions may result in increased or decreased emission estimates depending on the type of tank and operating scenario at the individual facility. It is expected that most emission estimates will remain close to the previously estimated values, however it is possible to have significant changes which may need to be discussed with the regulatory agency.


For more information and assistance in this regard please contact A & M Engineering and Environmental Services, Inc. (A & M).


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