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Highlights from RSL Dispersion Modeler's Workshop "Stakeholder Day"

On the afternoon of Tuesday, July 12, 2022 EPA held “Stakeholder Day” of the 2022 Virtual EPA Regional/State/Local (RSL) Dispersion Modelers’ Workshop. This was the portion of the RSL Dispersion Modelers’ Workshop that was open to “stakeholders” in the modeling community, which essentially means consultants and industry along with regulators. Following the Stakeholder Day, EPA and the other regulators have closed door meetings to discuss modeling policies/updates amongst themselves.

For those of you who weren’t able to make it for Stakeholder Day, here’s a quick rundown of what was talked about.

There were more than 300 attendees logged on throughout the afternoon. The first portion of the afternoon was spent going into detail on the updates to the AERMOD modeling system with the release of version 22112 (you may have noticed that it was released on June 27 which is Julian Day 178, not 112…well, EPA explained the 112 corresponded to April 22 when they locked down the code). On the AERMOD side it was pretty much bug fixes and new ALPHA/BETA options, and there’s also a new source type “SWPOINT” which has been introduced mainly to facilitate research on building downwash issues.

As for AERMET that update was primarily to “modernize” the code; having been written decades ago the code had become quite convoluted which made it very difficult for EPA to update. EPA emphasized that there were no changes to any of the equations so there’s no need for any regulatory action. From the user’s perspective the biggest change will be that AERMET now runs in only two stages (as opposed to the previous three) and there is now an option to run AERMET all at once.

The Model Clearinghouse has been mostly focused on modeling issues over water. That only affects a small number of modeling stakeholders, but if you’re modeling an offshore oil platform or a wind farm off the coast it’s a big deal. EPA’s recommended model, OCD (Offshore and Coastal Dispersion Model) is quite out of date—for instance, it doesn’t produce concentrations in the proper form to compare with today’s NAAQS and it even has to be run on a Windows 95 machine. Unfortunately using AERMOD as a substitute isn’t straightforward as AERMET doesn’t process overwater meteorological data. All that said, look for some modifications to AERMET in the future that incorporate the Coupled Ocean Atmosphere Response Experiment (COARE) to enable AERMET to run over water.

EPA was excited to announce that its PM2.5 and Ozone Modeling Guidance should be issued on July 29, with a release webinar in mid-August.

Looking ahead to next year, EPA is planning to hold an in-person 13th Conference on Air Quality at their offices in Research Triangle Park, NC. As far as Conferences on Air Quality go this won’t be as significant as some in the past, but look for some minor regulatory updates to the Guideline on Air Quality Models and some model formulation revisions.

EPA also talked about their AERMOD improvement priorities, which are as follows:

· Overwater modeling (downwash, shoreline fumigation)

· Building downwash (propose updates to PRIME from current ALPHA options)

· NO2 conversion (testing of GRSM and TTRM/TTRM2)

· Mobile source modeling/RLINE (promote from BETA option to regulatory option)

· Plume rise (add aircraft source type and incorporate plume rise algorithm as BETA option)

· Low wind (evaluate current low wind options against field data)

· Urban meteorology

Finally, on a related note, the modeling community will be gathering—in person—in a few months (September 13-15) in Durham, NC for the Air and Waste Management Association’s “Guideline on Air Quality Models: Developing the Future.” EPA promised to be there “in listening mode” to hear what folk in the modeling community are thinking.

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