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From his home outside Ciudad Juarez, Martin Guzman drives downtown every day to Ferreteria El Porton, the hardware store he owns nextto his brother's autobody shop and his sister's dental practice.

"Pollution starts on the edge of the city," he says. Air pollution, that is. Busloads of workers bounce over unpaved roadson their way to factory jobs, raising clouds of dust. Rock-crushing operations and concrete plants send particulates skyward in their race to keep up with the city's explosive growth. Aging automobiles sputter and belch in traffic, which swells daily withnew arrivals.

As municipal trash collection falls further behind, neighborhoods take to incinerating trash in vacant lots. Lacking other fuel, slum dwellers burn cardboard or tires for wintertime warmth. All this in a valley sandwiched between the Franklin Mountains on the north and the Juarez Mountains on the south.

"It's like living in a Dixie Cup," says Laurance Nickey, director of the El Paso City-County Health District. Between November and April, frequent thermal inversions act like a Saran Wrap seal to lock in the haze overhead. Juarez and El Paso being "one community that happens to be divided by a river," as Robert Cook of the Greater El Paso Chamber of Commerce puts it, they share the pollution that Juarez generates. El Paso is in violation of Environmental Protection Agency (EPA) standards for ozone, carbon monoxide, and particulates.

Archie Clouse, director of the El Paso district for the Texas Air Control Board, says a few maquilas pollute the air. But he disputes as "maquila-bashing" the notion popularized by the media that those factories cause the problem. On the contrary, he says, the problem existed long before the rise of the maquilas, and did not worsen from their operation.

El Paso began selling oxygenated gasoline last winter, a year before the new Clean Air Act required it. But state implementation plans say that the city may not meet EPA standards because of its neighbor.

Says Mr. Clouse: "The road to clean air lies through Juarez, Mexico."