Coal-fired power plants were the main source of the 10.6 million tons of sulfur dioxide. That total compared with 10.2 million tons in 2002 and reverted to the level from 2001.
Nonetheless, pollution from sulfur dioxide has dropped significantly over the past two decades, from 17.3 million tons in 1980 to 11.2 million tons in 2000, the year before President Bush took office. The total is within striking distance of lawmakers' goal of cutting such emissions to 8.95 million tons by 2010 — about half of the amount from 1980.
The Environmental Protection Agency released the information as part of an annual report required by Congress.
Agency chief Mike Leavitt and other EPA officials attributed the pollution increase last year to market trading, which is one aspect of the program to reduce acid rain. A power plant that has polluted more than it was allowed can buy credits from a plant that is under the limits of its allowable emissions.
Market trading also lets plants bank reductions in emissions beyond what was required and get credit for those in later years, which is what EPA officials say is responsible for the increase in 2003.
Agency officials pointed out that market-based programs for reducing pollutants typically result in big reductions early on; the acid rain program began in 1995. They predicted the increase would not last another year.
In a separate report, usually released at a different time of the year, the EPA estimated that total emissions of sulfur dioxide and the five other main pollutants targeted by the Clean Air Act had dropped in 2003. Environmentalists said the report was released now to overshadow the increase in sulfur dioxide pollution.
The Bush administration was "trying to mask this huge increase in sulfur," contended John Stanton, a senior attorney for an advocacy coalition that includes National Environmental Trust, U.S. Public Interest Research Group and Clean Air Task Force.
The five other pollutants are carbon monoxide, nitrogen oxides, particulate matter or soot, volatile organic compounds and lead. Emissions of those dropped nearly 2 percent, from 150.2 million tons in 2002 to 147.7 million tons in 2003, the EPA estimated.
"The air is cleaner than it was a year ago, it's cleaner than it was two years ago," said Leavitt, who spoke to reporters in a teleconference call from Concord, N.H., where he was presenting the information to the Society for the Protection of New Hampshire Forests.
"The air is the cleanest it's been in three decades but we're not done yet, obviously," he said. "There's a lot that we can learn from the acid rain experience of the last decade. It's a very efficient program."