Using COARE Algorithms in AERMET

With the recent publication of the updated Guideline on Air Quality Models (Appendix W to 40 CFR Part 51), the U.S. EPA incorporated the Coupled Ocean-Atmosphere Response Experiment (COARE) algorithms into AERMET. The addition of COARE allows AERMET to seamlessly calculate boundary layer conditions for overwater marine environments, and the promulgation of COARE as regulatory default model option eliminates the need for alternative model demonstrations.

In AERMET View V13.0, users can invoke the COARE algorithms via the Sectors inputs:

COARE Options in AERMET View V13.0

The COARE inputs consist of three primary selections: Surface Roughness, Mixing Height, and Additional Options.

Surface Roughness

This is a required option to process COARE. The default selection – Surface friction velocity (u*) – is considered the default selection. The alternate options use direct wave measurements or calculate those based on relationships for a well-developed sea state.

Mixing Height

Modelers are required to select one of the six options to calculate mixing heights. Full descriptions of these methods are provided in the U.S. EPA’s AERMET User Guide (see Section 3.7.7.6).

Additional Options

The remaining COARE selections are optional and should be based on the characteristics of the input data. These include:

• Defining the precise depth of sea-surface temperature measurements
• Overriding the default mixing height for wind gust calculations
• Setting minimum allowable values for mixing height and Monin-Obukhov Length scale
• Modifying the default vertical potential temperature gradient
• Invoking Warm Layer or Cool Skin options

Modelers are encouraged to review current U.S. EPA guidance on the use of these options as some are explicitly not recommended for regulatory applications.

Further information on the testing and evaluation of COARE is available on the U.S. EPA’s website: https://www.epa.gov/scram/2024-appendix-w-final-rule.

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