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Changes in AP-42 Temperature Equations



In March 2020, the U.S. EPA revised the emission calculation methods used in AP-42 Chapter 7.1 (Organic Liquid Storage Tanks). Nearly a year after the EPA posted the final revisions to this section, many state agencies and other regulatory bodies are - or soon will - be requiring use of these latest emission methods and meteorological data for permitting and emission reports.

A large portion of the updates to AP-42 Chapter 7 included the addition of API estimation methods for tank cleaning emissions. There were also a handful of minor changes that will affect how emissions are calculated.

Temperature equations, including average liquid surface temperature, average vapor temperature, and bulk liquid temperatures for insulated and partially insulated tanks have all been updated. These equations are now based off of tank dimensions to estimate the temperature change within the bulk liquid. More significant changes were made to the backbone of AP-42, including updated meteorology values, updated paint solar absorbance factors, and even updated Antoine coefficients for petroleum products.

What we generally have experienced as a result of these changes is an increase in VOC and HAP emissions, depending on the configuration of the tank, but also based on updated meteorology with higher ambient temperatures. It is now necessary for tank operators to determine whether these new algorithms will increase emissions and whether terminals are pushed to their permit limits. A careful assessment should be conducted to decide if the updated AP-42 equations and emission factors will require re-permitting your facility, or at a minimum, a frank discussion with your permitting authority.

So, what does this mean for your 2020 reporting year? Now that these changes are final, many agencies, including Louisiana DEQ and Texas CEQ, are no longer accepting permit applications that use the outdated equations. Many permitting authorities will no longer accept emission reporting that does not use the latest algorithms. It behooves owners and operators to get ahead of the curve on these changes rather than risk non-compliance. Facilities that are still using the EPA’s TANKS 4.09d (yes, somehow with all the errors some are still using it) will also need to find an alternate method of calculating emissions.

Fortunately, there are third parties who are familiar with the rigorous equations in AP-42 and provide services to help with any emission calculations you might need. CFR is the industry leader in aboveground storage emission templates, with customizable spreadsheets and software updated with the new AP-42 ready for use!

CFR personnel have been helping aboveground storage tank operators through the air emissions and associated permitting for over 30 years. Contact CFR for guidance on determining how this update affects your terminal.