On December 16, 2011 U.S. EPA issued a highly anticipated final rule regulating air toxic and mercury emissions from coal and oil fired electric generating units (EGUs). The mercury and air toxic standards (MATS) rule sets national emissions standards for hazardous air pollutants for power plants.


Affected Sources:

Affected sources include all coal and oil fired EGUs greater than 25 megawatts (MW) used to generate steam for electricity production for sale. The rule affects roughly 1,400 EGUs: approximately 1,100 existing coal-fired generating units and 300 oil-fired steam units.

The rule establishes two major subcategorizes, coal and oil. The subcategories include two for coal; low rank coal and not low rank coal, integrated gasification combined cycle (IGCC) EGUs burning synthetic gas, solid oil derived fired EGUs, and four subcategorizes for liquid oil fired units inside and outside the continental United States as well as units that are used on a limited basis.

Emissions Limits:

The MATS rule establishes numeric emission limits for mercury (Hg), particulate matter (PM) and hydrochloric acid (HCl) for existing source under the National Emissions Standards for Hazardous Air Pollutants (NESHAP) and sets numeric emission limits for PM, sulfur dioxide (SO2) and nitrogen oxide (NOX) for new sources under the New Source Performance Standards (NSPS) provisions of the Clean Air Act (CAA).

The rule establishes alternative numeric emission standards, including SO2 (as an alternate to HCl), individual non-mercury metal air toxics (as an alternate to PM), and total non-mercury metal air toxics (as an alternate to PM) for certain subcategories of power plants. For all EGU subcategories the rule establishes a work practice standards for organic HAP. During periods of startup and shut down the rule establishes work practice standards in lieu of numeric emission limits as initially proposed.

The final rule allows affected existing source to average their emissions if the units are within the same facility and within the same subcategory. New sources may not average their emissions.

The rule establishes an alternate emissions averaging compliance approach for mercury emissions from existing sources within the same subcategory. The alternate approach sets a 1.0 lb/TBtu Hg emission limit based on a 90 day boiler average as compared to 30 days.

Table 1 Existing Source Emission Limits
Filterable PM
Hydrochloric Acid* (HCL)
Existing- Not Low Rank Virgin Coal
0.03 lb/MMBtU
0.002 lb/MMBtU
1.2 lb/TBtu
(0.3 lb/MWh)
(0.02 lb/MWh)
(0.013 lb/GWh)
Existing- Low Rank Virgin Coal
0.03 lb/MMBtU
0.002 lb/MMBtU
1.1 lb/TBtu
(0.3 lb/MWh)
(0.02 lb/MWh)
4.0 lb/TBtu **
Existing IGCC
0.04 lb/MMBtu
0.00050 lb/MMBtu (0.0050 lb/MWh)
2.5 lb/TBtu (0.030 lb/GWh)
Existing solid oil derived
0.008 lb/MMBtu
0.0050 lb/MMBtu
0.2 lb/ TBtu (0.002 lb/GWh)
(0.09 lb/ MWh)
(0.08 lb/MWh)
New- Not Low Rank Virgin Coal
0.007 lb/MWh
0.0004 lb/MWh
0.0002 lb/ GWh
New- Low Rank Virgin Coal
0.007 lb/MWh
0.0004 lb/MWh
0.04 lb/GWh
0.07 lb/MWh
0.002 lb/ MWh
0.003 lb/GWh
New – Solid oil derived
0.02 lb/MWh
0.0004 lb/ MWh
0.002 lb/ GWh

Power plants will have three years to install pollution controls, as required by the CAA, with the possibility of receiving one-year extensions on a case-by-case basis. Additionally, the final rule allows utilities, to enter into an administrative order, to schedule an additional year to install controls. If the enforcement route were taken affected source could have up to 5 years to comply.

For more information on the MATS rule, please visit http://www.epa.gov/airquality/powerplanttoxics/actions.html