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Air Toxics: Additional Points

The N.C. Division of Air Quality (DAQ) enforces both federal and state requirements for controlling toxic and hazardous air pollution.  Under federal rules, certain industries must install state-of-the-art controls - or Maximum Achievable Control Technologies (MACTs) - if they emit hazardous air pollutants above specified threshold levels.

The U.S. Environmental Protection Agency (EPA) sets federal MACT standards by industry groups, such as chemical plants, pulp and paper mills, and furniture manufacturers.  MACTs generally specify processes or controls that facilities must use to limit their emissions of hazardous air pollution.


In addition to EPA regulations, North Carolina has a separate air toxics rule that is health-based rather than technology-based.  The state rule sets health-based limits for 97 compounds, 21 of which are not regulated under the federal program.  Facilities subject to the toxics rule must demonstrate that their emissions do not exceed these limits, known as Acceptable Ambient Levels, or AALs.


The first step in the toxics review process is to determine whether a facility’s emissions would exceed certain threshold levels that would trigger a more detailed examination.  If emissions are below threshold levels, then their emissions would not exceed the state’s health-based limits for air toxics.


If emissions are above threshold levels, facilities must conduct detailed computer modeling of their emissions of key pollutants.  The modeling takes into account factors such as emission rates, heights and locations of stacks, weather data and terrain to predict whether concentrations of any air toxic compounds would exceed any state AALs. If models show that emissions would exceed AALs, facilities must install controls or limit production as needed to comply with the limits.


Key industrial sources of air emissions in Haywood and Gaston counties have undergone review by the DAQ to make sure they comply with the federal and state air toxics rules.  These sources include Blue Ridge Paper in Canton as well as Freightliner, Firestone, FMC and Wix Filtration (now Affinia Group) in the Gastonia area. These sources have reviewed some or all of their toxics emissions. At least one facility, RadiciSpandex, has shut down since 2005.

All of these sources have demonstrated compliance with the state toxics rule.  In some cases, their toxic emissions were below threshold levels. Some facilities conducted detailed modeling that demonstrated compliance with AALs. In other cases, facilities agreed to limit their production levels or add control devices to achieve compliance.

In addition to the toxics reviews for industrial facilities, the DAQ monitored the air in Haywood County (Canton) for various toxic air compounds in May 2006.  That monitoring study showed that levels of pollutants were well below the AALs for most compounds that were measured.  The exceptions were formaldehyde, acetaldehyde, methyl mercaptan and hydrogen sulfide -- which were measured at levels moderately higher than the AALs.  More detailed analysis of the data showed that mobile sources (cars and trucks) were the likely sources for some of these compounds rather than industrial facilities in the area.