EPA has published a final national emissions standard for hazardous air pollutants (NESHAP) for gas-fired stationary spark ignition reciprocating internal combustion engines built before June 12, 2006. 75 Fed. Reg. 51,569 (8/20/10). The rule will require operators of these engines to control emissions of hazardous air pollutants (HAPs), such as formaldehyde, acetaldehyde, acrolein, methanol, and benzene. It sets emissions standards for spark ignition engines that are both major sources and area sources of HAPs.  

Major sources are those that emit 10 tons per year or more of one HAP or 25 tons or more per year of any combination of HAPs, and they are subject to maximum available control technology (MACT) standards. Area sources are those that emit less than the major-source threshold and are subject to the less stringent generally available control technology (GACT) standard. EPA agreed to issue the standards as part of a settlement. Sierra Club v. Johnson, No. 01-1537 (D.D.C. 3/31/06). The final rule will amend subpart 2222 of 40 C.F.R. part 63 and will take effect October 19, 2010.