In March, the Environmental Protection Agency will decide whether to lower the threshold for acceptable ground-level ozone amounts, and governmental bodies across the state have lined up to oppose the change.

The most recent to do so was the city of Las Vegas, joining Clark County, the Nevada Department of Transportation, the Nevada Department of Environmental Protection and Gov. Jim Gibbons.

The governors of 10 other states, as well as the National Association of Manufacturing, have expressed opposition.

The current standard calls for ozone levels not to exceed 80 parts per billion when averaged over an eight-hour period. One part per billion is about equal to one drop of water in an Olympic-size swimming pool.

The new standard would lower that acceptable concentration in air people breathe to 70-75 parts per billion.

"We don't have the ability at this point in time to meet that standard," said Ransel. "It's going to be very difficult to get below 80 parts per billion."

Transportation officials are worried about what failing to meet a new standard could mean.

"To force states to comply with the air quality rules, the federal government can withhold transportation dollars, supposedly as an incentive," wrote NDOT Director Susan Martinovich in a letter to the EPA.

"The new, more stringent rules could be devastating since we already operate under a federal highway funding program that is not keeping up with growth."

Added Dan Musgrove, a local lobbyist who's working with the National Association of Manufacturing: "If the standard were to go lower, there isn't anything Nevada could do except take more cars off the road."

EPA officials say Clark County, like many other areas in the West, probably will be designated a nonattainment area if the more strict, proposed standard is adopted. That means the county will have three years to develop an acceptable plan that will demonstrate attainment.

Ozone controls the county could put in its plan include a ride sharing program, reducing the number of diesel trucks on the road and requiring that cleaner-burning gasoline be sold during the summer.

Karina O'Connor, an environmental engineer with the EPA's planning office in Carson City, said "it's a remote possibility" that Clark County would lose federal highway funding.

"It would be pretty far out in the future before something like that could happen," she said in a telephone interview Monday.

In order for the EPA to even consider loss of highway funding, the agency would have to show that the county hasn't followed through with its plan. "I would say it's pretty remote at this point," O'Connor said.

As it stands under the existing eight-hour standard, Clark County is "on the border," she said, having complied for three years from 2004 to 2006. The county, however, dropped into the nonattainment range last year with a violation of the standard in August.

Western states face unique challenges in dealing with ozone, according to Ransel and the NDEP.

"They really don't look a lot out West," Ransel said of federal regulators. "They don't really understand how ozone reacts in the West."

Comments from Clark County and NDEP argue the same points:

• Ozone moves to Nevada from other areas, including California, Canada and Mexico.

• Normal ozone levels are higher in the West because of higher elevations and the arid climate leads to longer ozone life.

• The 70 parts per billion standard would be too close to "background" levels.

• Health studies backing the tighter standard were conducted mostly in Eastern metropolitan areas, and it's not clear whether ozone is the culprit or if it's "the synergistic effect of multiple pollutants."

The health studies objection is key because EPA officials cannot consider difficulties in compliance when evaluating the proposed rule.

"The Clean Air Act requires periodic review to make sure public health is protected," said EPA spokeswoman Margot Perez-Sullivan, noting that new evidence says ozone affects health at levels lower than the current standard.

"We can only take into account public health."

Most of the Earth's ozone is in the upper atmosphere, where it absorbs dangerous high-frequency ultraviolet light from the sun.

At ground level, ozone forms when vehicle exhaust, industrial emissions or some naturally occurring emissions react with sunlight. Breathing ozone can worsen bronchitis, emphysema and asthma, and reduce lung function and inflame the lungs' lining.

Several groups have supported the change, including the American Lung Association, the American Medical Association and the Sierra Club.

None of those groups responded to multiple requests for comment.

Review-Journal writer Keith Rogers contributed to this report. Contact reporter Alan Choate at achoate@reviewjournal.com or (702) 229-6435.