Significant revisions to the State Air Toxics Program were adopted March 13, 2014 by the North Carolina Environmental Management Commission.  The revisions were subsequently approved without any letters of objection by the Rules Review Commission (RRC) on April 17, 2014.  The effective date of the rules is May 1, 2014.


During the 2012 session of the General Assembly, HB 952 was enacted to exempt sources from the State Air Toxics Program that are Federally regulated. The legislation also required the Division of Air Quality to review the air toxics rules and identify additional changes to reduce unnecessary regulatory burdens on regulated sources and on DAQ resources.

Rule Revisions

The significant revisions are:

  • Sources subject to Federal NESHAPs, either MACT or GACT standards, are now exempt from State air toxics review unless the source would present an unacceptable risk to human health:
  • Only if DAQ determined in writing that a source presented an unacceptable risk to human health would an application for toxic emissions be required;
  • Exempted sources will be handled in the same simplified manner DAQ has used for sources subject to the wood furniture MACT;
    • A new, less conservative set of threshold toxic permitting emission rates (TPERs) for emissions from unobstructed vertical stacks have been established;
    • Clarification of  the use of actual rate of emissions in the air toxics rules, and
    • Deletion of the term “unadulterated wood”;
    • Elimination of the SIC Call;
    • Most natural gas and propane combustion sources are now exempt; and
    • Most emergency engines are now exempt.

A source not subject to a NESHAP, and thus not exempt, is required to submit either TPER calculations or, if emissions increases exceed the TPERs, a modeling demonstration that its toxic air pollutant emissions will not exceed the acceptable ambient levels (AAL).

Asbestos – A calculation error was recently found in the original determination of the AAL in the early 1990s.  The error, discovered by the Science Advisory Board on Toxic Air Pollutants (SAB), was five orders of magnitude (due to not using the total average number of deaths per 100,000).  As a result, the asbestos AAL was revised to 2.8 x 10-6 fibers per milliliter from the prior 2.8 x 10-11. This also resulted in a revision of the asbestos TPER to 5.7 x 10-3 lb/year.

One commenter requested the EMC to establish de minimis thresholds to exempt low levels of toxic air pollutant emissions. DAQ has indicated its agreement with this concept but needs to further study it and appropriate levels for such thresholds. DAQ is expected to initiate further rulemaking in the near future.

Arsenic – At its November 14, 2013 meeting, the EMC adopted revisions of the AAL and TPER for arsenic containing compounds, based on recommendations from the SAB. The AAL for arsenic containing compounds was revised from 2.3 x10-7 milligram per cubic meter (mg/m3) to 2.1 x10-6 mg/m3. The TPER was revised from 0.016 pounds per year to 0.053 pounds per year.  Prior to its review of these changes, the RRC received ten letters of objection. As a result, these changes are carried over to the legislature for its review. Unless the legislature acts to block or modify the changes, they should become effective by July 1 or August 1.

Click here to view the table.