Changes to Emission Estimations for Liquid Storage Tanks
AP-42 is the primary compilation of EPA’s emissions factor information and contains emissions factors and process information for more than 200 air pollution source categories. It is used by facilities as a source of emission factors when determining air emissions where site-specific emission factors through methods such as source testing are not available. Accurate determination of air emissions is required to identify facility source classifications and air permit requirements and when performing actual emissions calculations and emissions reporting.
In November 2019, the EPA published a revision to AP-42 Chapter 7, Section 7.1 – Organic Liquid Storage Tanks, which presents models for estimating volatile organic compound (VOC) emissions and, depending on material stored, speciated toxic or hazardous compound emissions. The emission estimation equations have been developed and updated by the American Petroleum Institute (API).
This emissions estimation reference replaces EPA’s TANKS Emissions Estimation Software (most recent version 4.09D, August 2012), which was developed on software that is now outdated. EPA has discontinued support for TANKS and recommends use of the AP-42 Chapter 7, Section 7.1 emissions equations.
Changes in the November 2019 revision of AP-42 Ch. 7.1 include:
- The use of average vapor temperature rather than average liquid surface temperature when calculating stock vapor density,
- New equations for partially insulated tanks,
- Working loss equations based on net working height rather than maximum liquid height,
- Working loss throughput calculated as a function of cumulative increases in liquid level,
- Updated Antoine’s constants for selected petrochemicals (Table 7.1-3),
- Updated values for paint solar absorptance (Table 7.1-6), and
- Updated meteorological data for selected US locations (Table 7.1-7).
State environmental agencies have begun requiring use of the November 2019 revision to AP-42 Ch. 7.1 for calculating emissions from organic liquid storage tanks. For example:
- TCEQ required air permit applications relying on AP-42 factors to use the updated emission factors beginning on December 16, 2019; and
- As of February 20, 2020, LDEQ will no longer accept air permit applications that rely on TANKS and air permit applications must use the November 2019 version of AP-42, Ch. 7.1.
VBA Compliance Assurance can assist you with updating your air emissions calculations and air permit determinations using the new AP-42 Ch. 7.1 emissions estimation techniques. If you need assistance with air permitting and/or air emissions reporting, contact a VBA professional.