The Roanoke Valley's ozone level has decreased by 16 percent since 1999, in part because of a regional reduction plan, officials announced Tuesday.

However, new rules implemented this year by the U.S. Environmental Protection Agency have put the region just shy of meeting the standard of 75 parts per billion -- a level that is "definitely feasible," said Mark McCaskill, a senior planner with the Roanoke Valley-Alleghany Regional Commission.

In 1999, the region's three-year average for ozone exposure over an eight-hour period reached an all-time high of 90 ppb. Last year, the level of ozone, a primary ingredient of smog, was down to 76 ppb.

That was cause for a brief celebration that ended last month, when the EPA implemented more stringent air quality standards that lowered the maximum allowable level from 85 to 75 ppb.

"At first, we felt like the grading scale had been changed before the final exam," McCaskill said of the new standard taking effect just as the region had reached compliance with the old one.

But McCaskill and others who attended a news conference expressed confidence that the valley will reach the new EPA standard. The way to do that, they said, is through a regional plan combined with actions by individuals.

In December 2002, local governments agreed to cooperate in an Ozone Early Action Plan. The plan urged the public and private sectors to take steps including purchasing more fuel-efficient vehicles, limiting the idling times of school buses, planting trees and encouraging car pooling.

"We take heart in the fact that we have already been successful at improving regional air quality, and that we can improve it further this summer to ensure that we remain in compliance with the new ozone standards," said Bradley Grose, the mayor of Vinton and chairman of the regional commission.

Ozone gets into the air through a variety of sources including automobile exhaust fumes, industry emissions and wind currents that carry pollution from elsewhere. Ozone levels are of particular concern during the summer, when conditions are most apt to form a pollutant that can cause breathing problems.

The state Department of Environmental Quality measures the valley's ozone level in Vinton, just downwind of the region.

A region's ozone average is calculated by taking the ozone level for the fourth-worst eight-hour period of the year. That number is then averaged with the fourth-worst periods from the previous two years.

In 2004, the EPA included the Roanoke Valley on a list of 474 areas with air-quality levels that did not meet federal health standards. By then, Roanoke, Roanoke County, Botetourt County, Salem and Vinton had adopted an early action plan to reduce ozone.

The plan, available only to regions with ozone levels at or near the federal standards, aims to improve air quality before it reaches a level that could result in federal sanctions such as stricter inspections of vehicle exhaust systems, emissions limits on new industries and the required use of more expensive reformulated gasoline.

Perhaps most importantly, McCaskill said, failing to meet the federal standards would have been "a black eye to a region that would like to market itself as a quality-of-life destination to live, work and play."

Roanoke and Winchester were the only two regions in the state to qualify for the early action plan. Winchester has reached a level that is just under the new 75 ppb standard.

Roanoke Valley officials hope to get the three-year average below 75 ppb by the end of the year. They met that goal in 2005 and '06, before the level climbed to 76 ppb last year.

"It's one person's actions, combined with all the other people in the region, that can make a difference," said Wayne Strickland, executive director of the regional commission. "So one person can make a difference," by car pooling, not mowing grass in the heat of the day or other measures.