SO2 NAAQS Implementation Update

U.S. EPA is continuing to move forward with the sulfur dioxide (SO2) National Ambient Air Quality Standards (NAAQS) Implementation process. U.S. EPA released their “Guidance for 1-Hour SO2 NAAQS SIP Submissions” draft document on September 22, 2011. The public comment period, which was initially set to close on November 2, 2011, was extended by a month until December 2, 2011. U.S. EPA has not yet released a final version of the guidance document. As we summarized in ALL4’s October “NAAQS Happenings” article and September “What’s Going on With the 1-Hour SO2 NAAQS Implementation Process” article, most states are waiting for U.S. EPA to finalize the guidance document before they move forward with the implementation process. However, note that several states, including Maine, Michigan, and Alabama, are being more proactive and have at least begun the process of requesting information from stationary sources that will be needed to conduct the modeling.

In other modeling related news, U.S. EPA’s Air Quality Modeling Group (AQMG) released a new version of the AERMOD air dispersion model on December 21, 2011. The updated version (11353) addressed a minor “bug” associated with updates to the previous version (11059) that incorporated options for modeling the new 1-hour nitrogen dioxide (NO2) and SO2 NAAQS. This new version of AERMOD (11353) will be used for all SO2 NAAQS SIP Implementation modeling.