Montana officials are asking the U.S. Environmental Protection Agency to reconsider designating Yellowstone County as violating federal standards on sulfur dioxide pollution.
The Montana Department of Environmental Quality bolstered its request with an April 3 letter with analysis the state agency says shows a trend for decreasing sulfur dioxide emissions.
The federal agency in 2010 adopted a new national one-hour standard of 75 parts per billion for sulfur dioxide to protect health, particularly for people with asthma, children and seniors.
The EPA at the time said Yellowstone County had an hourly concentration of 77 parts per billion based on information gathered from 2007-2009.
David Klemp of the state Department of Environmental Quality says state officials believe the EPA used unrepresentative information in making their decision.