Citing health and clean air benefits, Leavitt signed the proposal in St. Louis that would result in the largest cuts in SO2 and NOx emissions from power plants in more than a decade.

The City of St. Louis and nine surrounding counties were recently identified by EPA as having unhealthy air because of elevated levels of ozone. Next February, Missouri and Illinois will recommend to EPA whether those same localities meet health standards for particulate pollution.

Earlier in the week Leavitt signed a proposal for controlling mercury emissions from coal-fired power plants.

The proposed Utility Mercury Reductions Rule seeks comments on two approaches for reducing the estimated 48 tons of mercury currently emitted each year by coal-burning power plants in the United States.

The first approach would require coal-fired power plants to install currently available pollution controls known as "maximum achievable control technologies" (MACT) under section 112 of the Clean Air Act. If implemented, this proposal would reduce nationwide emissions of mercury by 14 tons (29%) by the end of 2007.

The second approach would set a mandatory, declining cap on the total mercury emissions allowed from coal-burning power plants nationwide. This approach, which allows emissions trading, would reduce mercury emissions by nearly 70% from current levels once facilities reach a final mercury cap, which takes effect in 2018.

The EPA said the longer-term cap and trade approach would deliver far greater benefits than the command-and-control alternative.

“The cap-and-trade approach under the proposed rules would require power plants to meet strict emission caps in two phases. Strict caps, coupled with the flexibility of emissions trading, provide a continuously increasing reward for innovation and the deployment of more effective and less-costly pollution-reducing technologies,” EPA said.

Adoption of the cap and trade approach would require EPA to revise its December 2000 finding that it is "appropriate and necessary" to regulate utility hazardous air emissions using MACT standards. EPA proposes such a revision as part of the package of proposed actions.

On SO2 and Nox emissions, the EPA said the Interstate Air Quality proposal would reduce power plant emissions in a total of 29 eastern states and the District of Columbia in two phases.

Sulfur dioxide emissions would drop by 3.6 million tons in 2010 (a cut of approximately 40% from current levels) and by another two million tons per year when the rules are fully implemented (a total cut of approximately 70% from today's levels).

NOx emissions would be cut by 1.5 million tons in 2010 and 1.8 million tons annually in 2015 (a reduction of approximately 65% from today's levels). Emissions will be permanently capped and cannot increase.

Leavitt noted that Washington University in St. Louis has for the past three years been a lead institution in a detailed collaborative study of fine particulate air pollution. Researchers, using a US$3.5 million EPA grant, are studying air pollutant levels, personal exposure and health ramifications.