The U.S. EPA finalized the new 1-hour primary National Ambient Air Quality Standard (NAAQS) for SO2 on August 23, 2010.  The new standard requires new or modified sources that trigger Prevention of Significant Deterioration (PSD) permitting to demonstrate compliance with the new 1-hour SO2 NAAQS through an air quality modeling analysis.  In addition, the rule requires the Ohio EPA to determine which areas in the state are attaining the new 1-hr standard.  As outlined in the preamble to the final rule, U.S. EPA has provided they will "not consider ambient air quality monitoring alone to be the most appropriate means of determining whether all areas are attaining a short term NAAQS," and provides that states should also utilize the "superior utility that modeling offers for assessing SO2 concentrations."  In response to this requirement, several states, including Ohio, have embarked on modeling to support attainment designations for the new standard.  Unlike states such as Indiana and Illinois, the Ohio EPA has taken a more focused approach by limiting the initial modeling effort to those areas surrounding the seven existing ambient monitors that show nonattainment with the new NAAQS.  These ambient monitors are located in Belmont, Columbiana, Cuyahoga, Jefferson, Lake, Meigs, and Morgan counties. 

In developing this first round of modeling, Ohio EPA initially contacted 20-30 large sources of SO2 emissions located in these seven counties for the data necessary to perform the modeling (e.g., stack parameters, building data).  However, upon further guidance from U.S. EPA, Ohio EPA expanded the modeling domain to a 50 kilometer (km) radius around each monitor.  Ohio EPA is currently working with 10-15 additional sources of SO2 emissions to address the expanded modeling domain in these seven areas.  By June 2013, Ohio EPA will be required to conduct additional modeling for the remainder of the state and expects to initiate additional data requests from significant sources of SO2 emissions to support this more expansive modeling effort.

For more information about this article please call Kirk Lowery at 614-433-0733.