SO2 Attainment Status

On February 13, 2013, NCDAQ announced that the entire state was now in compliance with the new, much more stringent 1-hour SO2 National Ambient Air Quality Standard (NAAQS):
The New Hanover County monitor had exceeded the NAAQS as recently as the 2009-2011 time period, prompting NCDAQ to reach out to Wilmington area sources to help conduct modeling analyses that would yield attainment or at least limit the extent of nonattainment. With the shutdown or relocation of significant SO2 sources that were in close proximity the monitor, along with reduction in sulfur emissions from other fuel oil burning sources, 2012 monitoring values were substantially reduced from the previous 3 years. Based on the most recent period (2010-2012) the New Hanover monitor is below the 1-hour SO2 NAAQS and is expected to remain that way with the conversion of the Sutton Steam Generation plant from coal to natural gas and a trend of other sources towards burning lower sulfur fuels.

Updated Meteorological Datasets for Modeling

The U.S. EPA released a new version of the AERMOD model in late 2012 (version 12345). As part of that update, the meteorological preprocessing program, AERMET was also updated. NCDAQ has processed new meteorological datasets in the latest version of AERMET, using the most recent 5 available years (2008-2012) for many new stations beyond what was previously provided:

These datasets were generated with the latest U.S. EPA guidance and include the use of hourly winds based on the average of all the 1-minute wind speed readings in a given hour. Previously, only the standard hourly observation (generally recorded at 10 minutes prior to the hour) was included in the data record. If the winds were calm at that observation time, the entire hour was set to calm, which is ignored by AERMOD. With the inclusion of the 1 minute wind measurements, many of the calm hours that were in the older model-ready datasets have been replaced with low wind speed values, which introduce poor plume dispersion conditions. Trinity’s experiences with the new datatasets have shown higher (sometimes significantly so) modeled impacts. As such, facilities involved in ongoing permitting actions requiring modeling as well of those planning expansions or changes in the near future should be aware of the potential impact of these new datasets.