4 The record articles

10th Conference on Air Quality Modeling

Posted: March 21st, 2012

Author: All4 Staff 

ALL4 attended and presented at U.S. EPA’s 10th Conference on Air Quality Modeling in Research Triangle Park, NC March 13th through 15th.  The purpose of the conference, mandated by Section 320 of the Clean Air Act, is to provide an overview of the latest features of the U.S. EPA’s preferred air quality models and to provide a forum for public review and comment on how the U.S. EPA determines and applies air quality models in the future.  During the conference U.S. EPA summarized all of the model changes and memorandum guidance released since the 9th Conference on Air Quality Modeling held in October 2008.  In addition U.S. EPA presented on current projects that they are working on.  Much of the conference focused on issues with the new 1-hour nitrogen dioxide (NO2) and sulfur dioxide (SO2) National Ambient Air Quality Standards (NAAQS). 

The biggest “no news”, news from U.S. EPA is that there is still no date set for the final release of the “Guidance for 1-hour SO2 NAAQS SIP Submissions” that was released in draft on September 22, 2011.  U.S. EPA indicated that there were a large volume of comments received during the comment period from industry, environmental groups, and State agencies and that we should not expect a final version anytime before the end of 2012. This will significantly tighten the time frame for completing SIP maintenance plans that are due to U.S. EPA by June 2013.  Many States don’t believe that they will be able to complete the SIP modeling even if guidance is released today and don’t think U.S. EPA will be able to either if a Federal Implementation Plan (FIP) is undertaken.  Therefore, many states are continuing to wait and see how things shake out at this time.

The following are some of the other noteworthy plans outlined by U.S. EPA:

  • U.S. EPA intends to release clarification memos on:
    • Automated Surface Observation Systems (ASOS) vs. observer based National Weather Service (NWS) meteorological data.
    • The EPA formula for calculating Good Engineering Practice (GEP) stack height in AERMOD.
  • Pending new version of AERSURFACE that uses 2001 National Land Cover Dataset (NLCD).
  • Pending new version of AERMET that has changes to convective mixing height calculations and includes a minimum wind speed threshold option in stage 3 for use when incorporating AERMINUTE data.
  • Pending guidance for modeling PM2.5 precursors by the end of April 2012.
  • An update to 40 CFR Part 51 Appendix W is currently scheduled to be undertaken before the 11th Conference on Air Quality Modeling in 2014.  EPA plans to release the updates before the conference so that the regulated community can comment.

The 3rd day of the conference was open to the public to provide comments to U.S. EPA on the record.  Many of the presentations revolved around AERMOD’s overestimation of 1-hour concentrations especially during low wind speed events.  It seems that the introduction of AERMINUTE to help capture missing data has only introduced more low wind speeds which in turn are leading to overestimations of concentrations.  Due to issues with AERMOD over predicting 1-hour concentrations and in anticipation of air quality modeling for the SO2 NAAQS SIP process some facilities had begun ambient SO2 monitoring programs to collect actual SO2 data to dispute air quality modeling results.  Many States and facilities in the regulated community believe that this is a better option with showing compliance with the 1-hour SO2 NAAQS.  In addition the general consensus was that more field studies need to be undertaken to evaluate the models.  Currently most field studies used for model evolutions are from the 1970’s.  This is a big issue considering U.S. EPA’s plan to rely on modeling for the SO2 NAAQS SIP, so expect to see more monitoring data compared to modeling in the near future.


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