Many of the larger sources of toxic emissions, such as vehicles and power plants, have restrictions of one type or another on their emissions. Similar regulations on a class of smaller sources — stationary diesel and gas-fired engines — have been under development for many years during the Bush administration. EPA released a proposed rule on Feb. 25, 2009, as required by a consent decree with Environmental Defense. A final rule is required by Feb. 10, 2010.

More than one million of these engines are used in industrial, agricultural, and other settings, and they emit toxic substances such as formaldehyde, benzene, and acrolein. Many would be covered under the proposed rule, and likely would have to install some kind of mitigation equipment if the rule is approved. However, some of these engines that are newer, and of certain horsepower, would not be covered by the rule.

The 60-day public comment period ends May 4, 2009.

• Proposed rule, "Reciprocating Internal Combustion Engines: Proposed Area Source Air Toxics Requirements," fact sheet, [2] Feb. 25, 2009; EPA press release, [3] Feb. 27, 2009; Federal Register notice, [4] March 5, 2009, or search [5] for EPA-HQ-OAR-2008-0708 for the proposed rule, and comments on it.