The Commission for Environmental Cooperation of North America study compared emissions data from 899 plants in the Unites States with 82 plants in Mexico and 70 in Canada. The study revealed higher levels of sulfur dioxide, nitrogen oxide, carbon dioxide and mercury pollution in the US than in Mexico and Canada.

The commission found that Mexico, which sources around 8% of its energy from coal, had the top sulfur dioxide and nitrogen oxide emitting plants on the continent.

The report has fuelled ongoing criticism of coal-fired plant emissions. "Our emissions are very high and underscore that relatively few power plants are using modern pollution control equipment 35 years after the passage of the Clean Air Act," Frank O'Donnell of Clean Air Watch told the Pittsburgh Gazette.

Pennsylvania’s power plants are among the biggest emitters of sulfur dioxide and mercury pollution in North America - four of the top eight mercury-emitting plants and two of the top three sulfur dioxide-emitting facilities are located in the state.

Earlier in the month, the Environmental Protection Agency’s latest proposals to control mercury emissions from power plants drew attacks from a coalition of attorneys general from Connecticut, Massachusetts, New Hampshire, Vermont and Wisconsin.

The Natural Resources Defense Council and Clean Air Task Force said EPA has recently raised a "raft of issues unrelated to its statutory duty" to develop a stringent mercury, Greenwire reported.

The EPA was due to issue regulations on mercury emissions by December but the deadline was extended to March. Among EPA's mercury proposals are several alternative methods to cut emissions from coal-fired power plants. One of these is a market-based trading plan that moves away from the so-called MACT approach. Under this 2001 EPA ruling, power plants were required to install "Maximum Achievable Control Technology" on nearly all units.

EPA is now pushing for a cap-and-trade program for utilities which means power plants will no longer be compelled to install state-of-the-art pollution control technologies.

Criticism of this approach has suggested the trading plan would not sufficiently protect public health and the environment. But the Bush administration has argued a mercury rule with trading would ultimately reduce toxic emission levels from today's 48-ton range down to 15 tons, Greenwire reported.

Investors in power plants are eagerly awaiting the mercury ruling as it will have a flow-on effect in relation to what becomes the preferred technology.

If CO2 removal is required to a major degree, it is likely integrated gasification combined cycle (IGCC) will become the preferred power plant technology. This is largely because it would be cheaper to remove CO2 with IGCC by syngas shifting prior to combustion than post combustion.

There are currently two coal based commercial size IGCC projects operating in the US and two in Europe.