As the Obama administration considers further steps to fight air pollution, a recent report from a Washington think tank shows that air quality in the United States has improved significantly over the last decade.
The American Enterprise Institute for Public Policy Research analyzed data collected by the U.S. Environmental Protection Agency and concluded that levels of numerous gases linked with air pollution have fallen off since 2001.
Among the findings: Carbon monoxide decreased by 39 percent, ozone by 6 percent, and sulfur dioxide by 32 percent.
"Pick any category you want and pollution levels are generally lower than they were seven years ago," said Steven Hayward, the policy analyst who authored the report, titled "Index of Leading Environmental Indicators," for the conservative think tank.
"(Environmental groups) said air pollution was out of control, but this was always more about politics than it was fact," Hayward said.
Environmental groups agree that tremendous progress has been made since the 1980s, when cities like Houston and Los Angeles were thick with smog and acid rain devastated lakes and forests across the U.S.
But they add that the progress reflects "strong legislation," and they say the nation needs more of it.
"The reason we've had success over the last 40 years is because strong laws like the Clean Air Act work on pollution," said John Walke, an attorney with the Natural Resources Defense Council.
"But we have a long way to go. We've learned more. The science is better today than it was in 1980 or 1990. We now know we need stronger definitions of clean air to truly protect Americans.
"Over 150 million Americans live in areas with unhealthy air," Walke said. "If we can pass effective laws, we can reduce the problem."
In an e-mailed statement, the EPA said that it has seen success by a number of measures, but there are still key areas of the country "not meeting EPA's air quality standards."
President George W. Bush drew the ire of environmental groups throughout his eight years in the White House, perhaps the loudest in 2003 when he announced that he would end a Clean Air Act program that required older power plants, refineries and industrial sites to install pollution control devices when they expanded their operations.
But in looking over the data on air quality from the Bush years, Hayward notes that levels of most air pollutants decreased at a faster rate than they did during the Clinton administration.
"Mostly of it's technological change. Quite a bit of it's been forced by regulation, but a lot of it has been the marketplace," Hayward said. "The EPA has models that project an 80 percent decline in auto emissions. Nothing Bush could have done was going to change that."
Responding to Hayward's report, the EPA said it did not correlate drops in pollution levels to specific presidential decisions.
"Air quality regulations and progress overlap administrations," the agency said in a statement. "For example, ozone reductions that began in the East in 2004 resulted from a rule the agency issued in 1998."
Jeff Holmsted, a high-ranking official at the EPA from 2001-2005 and now an attorney with the law firm Bracewell & Giuliani, acknowledged that the decrease in air pollution over the last eight years owes much to efforts of past administrations. But he called the statistics a vindication of Bush's environmental policy, which he said did away with cumbersome regulations while still protecting the environment.
"I think among people who actually understand how the regulatory process works, they, in private, would acknowledge that we accomplished a lot," Holmsted said.
Hayward began putting out his annual report in 1994 due to what he called "the lack of unity on environmental responsibility in this country."
Every year he combs through EPA data to present what he believes is a more comprehensive portrait of the state of the environment than what the mainstream media have provided following events like the grounding of the Exxon Valdez oil tanker in 1989.
"Species extinction or nutrient run off from the Mississippi basin, these are big issues that get very little coverage," Hayward said. "It isn't a big catastrophe like a tanker crashing or a hurricane."
Hayward says his biggest gripe is the amount of media coverage given over to global warming.
He acknowledges that carbon dioxide levels are increasing in the earth's atmosphere, but he says there are gaps in global warming data, such as a recent trend toward cooler temperatures.
"We had temperature increases for two-and-a-half decades, but it suddenly seemed to switch a few years ago," Hayward said. "It might just be noise, but a lot longer and we'll have to think about it."
That might rub against the grain of environmentalists like Walke, who say the science behind global warming has improved dramatically over the last five years.
But for Hayward, the number of people that believe something is no indication that it's correct.
"If you look at survey data, what you find is three quarters of Americans think environmental quality is getting worse, but at the same time they tend to think their neighborhoods are getting better," he said. "People just don't have all the information."