21st Century North Carolina Air Quality

DAQ Studying Air Toxics and Boiler MACT

With the EPA's recent promulgation of MACT standards for combustion sources, the DAQ has begun studying the risk from air toxics emitted from combustion sources in North Carolina. A progress report was submitted to the Air Quality Committee of the EMC at its meeting on March 9, 2006. The initial study used the EPA's Human Exposure Model (HEM) as a screening tool to address the toxic air pollutants from nearly 2,000 combustion sources. The DAQ pointed out that the state has not yet seen substantive emission reductions resulting from the MACT standards for combustion.

The prelimary results indicate that the primary pollutant driving the cancer risk for coal-fired units is arsenic, while the primary pollutant for noncancer risk is acrolein. For wood-fired combustion units, the key pollutant for cancer is hexachlorodibenzo-p-dioxin, with acrolein the key pollutant for noncancer risk. The DAQ will conduct additional modeling of the "high risk combustion units" using an enhanced model (HEM-3).