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KAI RYSSDAL: Here's an oldie but a goodie from the pollution files: smog. It doesn't get much attention anymore with all the focus on global warming. But many scientists are urging the White House to toughen up U.S. smog standards. They say the government's not doing enough to protect public health. Especially children and the elderly, who're most vulnerable to respiratory problems.

From the Marketplace Sustainability Desk, Sarah Gardner reports now on growing concern over our dirty skies, and how ethanol's become part of the search for a solution.

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SARAH GARDNER: It's mid-morning on a hill high above the intersection of two busy freeways in Diamond Bar, Calif. That's the eastern-most edge of Los Angeles County, where the traffic grows heavier every year.

In the distance, you can see the snow-capped peaks of the San Gabriel Mountains. Well, sort of . . .

SAM ATWOOD: Uh, Mount Wilson? Uh, we can't really see through the haze this morning.

Sam Atwood works for the biggest air pollution district in the country.

ATWOOD: And even further off in the distance, obscured by the haze, would be Mount San Gorgonio, the tallest mountain in Southern California.

When that "haze" burns off by noontime, what's left is smog. And here at the South Coast Air Quality Management District, workers see plenty of it.

Everyday, more than 11 million cars and trucks clog the roads in their region, emitting the pollution that tinges the skies with a yellow-brown haze.

ATWOOD: Southern California has had the stigma of being the smog capital of the nation for decades, and frankly that's a title we'd like to lose.

But Southern Californians aren't the only ones breathing unhealthy air. Nearly 160 million Americans live in cities — and now suburbs — where smog levels exceed the legal limit.

Now, scientists at the Environmental Protection Agency are recommending even stricter limits on ground-level ozone, the main ingredient in smog. U.S. ozone standards haven't changed since 1997, and critics say it's long overdue.

Lydia Wegman directs the EPA's Health and Environmental Effects Division.

LYDIA WEGMAN: What the staff did is look at the science that has come out since 1997, as well as science before 1997, and we have dozens of new studies that have come out. And the staff concluded that the current standard is not sufficiently protective of public health.

Wegman's staff ended up recommending smog limits of anywhere from a little below .080 to .060 parts per million. Now that's Greek to most of us, and it's hard to quantify the benefits.

But Janice Nolan at the American Lung Association says if the nation's smog zones actually met those standards, the improvement will first be seen in doctor's offices and emergency rooms.

JANICE NOLAN: There is no question that if EPA sets a standard that provides the kind of safety levels that we're talking about, lives can be saved.

If ozone levels in New York City met the strictest standard under recommendation, Nolan estimates the Big Apple would see 40 percent fewer hospital admissions for asthma.

She notes that when Atlanta restricted traffic during the Olympics, ozone levels dropped dramatically. So did asthma attacks. Recent studies link dirty air to lung damage, heart disease and shorter life spans. And kids living near busy highways are especially vulnerable.

NOLAN: For the rest of their lives, they are at greater risk of all of the problems that come from lung diseases in the future. So it has enormous and widespread impacts.

EPA administrator Stephen Johnson will decide in June whether to change U.S. smog standards. Johnson has rejected the advice of science advisors before, and EPA has been sued as a result.

Meanwhile, scientists are debating how President Bush's push for more ethanol will affect smog levels. Ethanol actually reduces carbon monoxide, but increases evaporative emissions of another key pollutant. Clean air advocates are calling for more research.

In Los Angeles, I'm Sarah Gardner for Marketplace.