Despite Efforts, Clean Air Elusive

"You can really just see the pollution in the air, just how dull it is in between here," he said, gesturing at the haze above 17th and H streets NW.

Some of the week's worst air was measured Wednesday at a Howard University research center in Beltsville.

At 2 p.m., anyone drawing a breath there would also have drawn in about 95 parts per billion of ground-level ozone. This is a colorless gas that protects the Earth when it is in the upper atmosphere but is counted as a pollutant closer to the ground. The level in Beltsville was above the level that the Environmental Protection Agency considers safe for people with weakened health, which is 85 parts per billion.

Scientists say this smog does not actually come from tailpipes and smokestacks; it forms when compounds in those emissions are transformed by heat and sunlight. Even in small concentrations, ozone has been found to cause inflammation in the lungs and worsen such conditions as asthma.

"It's rubbing sandpaper on the lung tissue," said Janice Nolen, an assistant vice president at the American Lung Association.

The same breath would have drawn in a tiny amount, about one hundredth of a millionth of a gram, of what scientists call "fine particles." These bits of pollution often come from cars or power plants running on fossil fuels. They are often soot -- little, unconsumed pieces of something that was burned.

The level of these particles at Beltsville was not high enough to cause an alert. But local health officials said they were concerned because research has shown that the particles are so small they can bypass natural barriers in the nose and lungs. Once there, scientists say, the particles might aggravate breathing problems or heart conditions.

More days like this week's seem inevitable this summer: Last year, there were 19 Code Orange days, a Code Red day and a Code Purple one, the worst kind, when anyone spending time outdoors might risk "serious health effects."

Still, officials say they have made major progress in cleaning the region's air. In the past decade, they said, new government policies have decreased the amount of sulfur, a major contributor to smog, in gasoline. They have required cleaner-running engines in cars and trucks and cleaner emissions from power plants in the eastern United States. Locally, city and county governments have promised to buy more of their power from wind and retrofit buses to run cleaner.

And air monitors show the results of these changes: The worst ozone day in McLean last year was 21 percent better than the worst one in 1988. In the District, the worst day for particle pollution last year was about 25 percent better than in 1997.

But, because of days such as Wednesday and Thursday, the region does not meet the EPA's standards for smog. Many of its jurisdictions, including the District and Arlington, Fairfax and Prince George's counties, get an "F" in the American Lung Association's annual smog rankings.

Officials say that to reduce pollution further, residents will also have to change their habits.

"People need to look at themselves. On a bad air day, did they choose to drive an energy-inefficient vehicle?" said Nancy Floreen (D), a Montgomery County Council member who heads COG's air-quality committee. "Did they choose to travel more than they really, really needed to do?"