The Obama administration’s foot-dragging on establishing a new, science-based standard for exposure to ground-level ozone pollution—the main component of smog—is unacceptable, according to the Union of Concerned Scientists.

“The science has been in for three years. It’s past time to set the new standard,” said Francesca Grifo, director of UCS’s Scientific Integrity Program. “The law says the Environmental Protection Agency has to base its decision on the science. At this point, setting a standard outside the range scientists have determined is a clear violation of the Clean Air Act. The first step to protecting public health is setting the standard based on science.”

According to the Clean Air Act—and reinforced by a 2001 Supreme Court decision—ground-level ozone standards must be set solely according to the findings of EPA scientists and the EPA’s Clean Air Scientific Advisory Committee, an independent panel of experts. According to the law, states and localities can take economics into consideration during the implementation process.

The Obama administration promised in 2009 to revisit an unscientific Bush administration decision to define dangerous levels of ozone at 75 parts per billion. That decision, which was later challenged in court, disregarded public health scientists’ finding in 2007 that only a standard of 60 to 70 parts per billion was scientifically justifiable. In 2010, the EPA issued a proposed rule in that range. However, a final rule with a specific numerical standard has been repeatedly delayed.

The EPA, meanwhile, has consistently defended its ability to set a science-based standard and called the Bush-era standard “not legally defensible,” but agency officials have been pressured by corporate interests and members of Congress to back down. A final rule is currently undergoing review by the White House’s Office of Management and Budget, which has historically interfered with science-based policy.

“Independent scientists determined in 2007 that the EPA must strengthen this standard to adequately protect public health, but nothing has happened since,” said Liz Perera, a UCS public health expert. “These continued delays are unacceptable. Every additional day of delay means more Americans will suffer.”

Last month, Perera and UCS Climate Scientist Todd Sanford released an analysis that found that rising temperatures due to climate change likely will increase ground-level ozone pollution and exacerbate health problems.