The day of reckoning has come for air pollution in the Treasure Valley.

Levels of ozone, the colorless gas that causes lung and heart damage and is the main ingredient of smog, crossed a key threshold Friday - all but guaranteeing the state will have to take painful new actions to reduce air pollution in the coming years.

State officials have used voluntary measures to encourage less driving, lawn mowing and other activities that pollute, but the state now will be forced by the U.S. Environmental Protection Agency to institute mandatory control measures, perhaps as soon as 2010.

Industries will have to reduce pollution if they hope to expand and even small businesses previously unaffected - like auto body repair shops, paint shops and gas stations - will face new regulations.

But the biggest impact will be on our driving habits, since auto emissions are the biggest source of the pollutants. The federal rules will force state leaders to take a harder look at expanding public transportation instead of widening roads to handle growth. And Canyon County drivers likely will have to submit to vehicle emissions tests.

There is still a faint hope that the state could avoid such mandatory federal controls if the state could reverse ozone pollution growth in 2009 and 2010. But that would take similarly dramatic state and local controls to reduce driving and curb other ozone pollution sources.

"My constituents are not interested in having the federal government come in and tell us what to do," said Sen. John McGee, R-Caldwell, chairman of the Senate Transportation Committee. "I'm hopeful that actions taken by the Department of Environmental Quality will get us pointed in the right direction."

Ironically, last week's air quality violation comes as high gas prices have reduced the number of miles Treasure Valley residents have driven this spring and summer. It also comes in a year that has been cooler and with fewer of the hot days that create the conditions that cause ozone to form.

"Last year, we would have violated this in May," said Leonard Herr, Idaho Department of Environmental Quality air quality regional manager.

Ozone is created when nitrogen oxides mix with volatile organic chemicals in heat and sunlight. As the temperature rose Friday, ozone pollution concentrated to 78 parts per billion, exceeding the federal standard of 75 ppb. It was the fourth time this year that levels exceeded 65 ppb. The bad air days, added to high ozone readings in the past two years, pushed the Valley into a violation of the federal standard.

Ada and Canyon counties are likely to have more high ozone days this summer. August is usually the worst month, Herr said.

The violation now begins a two-year process for the state to work with the EPA and for the EPA to formally declare that the state is in what the agency calls "nonattainment."

State and local officials will then have three years to submit a plan for bringing the two counties back within federal health standards. The Treasure Valley would have up to 20 years to comply.

But DEQ Administrator Toni Hardesty was hopeful that if the state can get ozone levels down by next year, it could have a chance of avoiding nonattainment status.

Elin Miller, EPA Region 10 administrator in Seattle, said the agency will work with Idaho to help meet the standards, but local officials should not expect to get off the hook.

Regulations that require gas stations to capture volatile organic compounds - the vapors in underground gas tanks - could be in place next year. But new emissions testing for Ada and Canyon counties, approved by the Idaho Legislature earlier this year, is not expected to be in place until 2010, unless local governments impose it themselves, Herr said.

As early as June 2010, transportation planners will have to demonstrate that any new road project will not increase pollution. Small businesses like painters and body shops would immediately face new regulations. And pollution levels for existing and new industries would be capped, which could limit economic expansion.

Some businesses are already preparing. Kelly-Moore Paint Co., for example, offers many paint products without volatile organic compounds, said Jason Kemper, manager of the store on Broadway.

Bus ridership is up 10 percent so far this year, and the number of riders on buses between Ada and Canyon counties has risen an astounding 77 percent, said Mark Carnopis, a ValleyRide spokesman.

But expansion of the bus system is limited, as is funding; fares cover only a part of the bus system's costs.

Herr said DEQ has sought incentives for state workers to take public transportation, but current state law prevents it. He also said he would like to see incentives that encourage others to ride the bus, but those cost money, too.

"Getting people on the bus for the first time is the key," Herr said. "It's kind of like a snowball effect."

Rocky Barker: 377-6484