Not only are many major American metropolitan areas suffering from problems in their inner cities, but they're also ailing environmentally. Even though manufacturing isn't the sole cause, it's an unfortunate reality that where manufacturing locates, environmental challenges and controversy often follow. Chicago and Houston illustrate the point. Although their MSAs don't exactly correspond with the air-monitoring jurisdictions of the federal EPA, the agency classifies both as "severe nonattainment areas" for their failure to meet federal standards for the presence of ground-level ozone, the main component of urban smog. Only the notoriously smoggy Los Angeles basin, the lone area in EPA's "extreme" nonattainment classification, has higher ozone levels. But Chicago and Houston aren't alone in their "severe" nonattainment status. Seven other areas share the distinction, at least until the agency performs a reclassification in November. Five of them -- Milwaukee/Racine, New York/Northern New Jersey/Long Island, Baltimore, Philadelphia/Wilmington/Trenton, and Sacramento -- roughly correspond to MSAs that rank in the upper 20% of IW's listing of locations for manufacturing. Moreover, Chicago and Houston fare poorly in another key environmental measure -- emissions of toxic chemicals. A Sierra Club listing of the "20 Most Threatened Counties" for cancer-causing pollution puts Harris County, Tex., in which the city of Houston is located, at the very top. Cook County, Ill., Chicago's home county, is No. 2. The ranking was gleaned from data reported by companies through EPA's Toxic Release Inventory. To be sure, as in all metro areas, the blame for pollution shouldn't be pinned entirely on local manufacturers. In Chicago, much of the ozone problem "is caused by coal-fired powerplants that are upwind and could be hundreds of miles away," acknowledges Jack Darin, Illinois state field representative for the Sierra Club's Chicago chapter. "We [Chicago] have made a lot of progress in the last 20 years in cleaning up our air, and we've implemented the basic control strategies required by the Clean Air Act. But we still need new reductions, a lot of which will come from sources of pollution that have not been reduced significantly." Automobiles, of course, also are a prime dirty-air culprit. In Houston, a sprawling metro area with poor public transportation, cars and other "mobile sources" account for 41% of emissions of nitrogen oxide, the key generator of ozone. But "point sources" -- industrial locations -- contribute 59%, largely emissions from the metro area's array of petrochemical plants and oil refineries. Point sources, however, account for only 34% of the area's emissions of volatile organic compounds (VOCs), the other major ozone ingredient. Some of the VOCs occur naturally. "Compared with Los Angeles, the Houston area is definitely lagging" in cleaning up its air, assesses Ramon Alvarez, staff scientist in the Austin office of the Environmental Defense Fund, a New York-based environmental group. But he's encouraged that officials of separate jurisdictions are beginning to attack the problem "on a regional basis." Not surprisingly, the Houston metro area is a prime target of environmental activists. Yet environmental agitation is even more intense in neighboring Louisiana, home to an estimated 20% of the U.S. chemical industry. There, Baton Rouge currently may be the nation's hottest environmental battleground. Local activists predict that the 140-plant strip of petrochemical facilities and refineries between Baton Rouge and New Orleans, which they dub "cancer alley," will be upgraded from "serious" to "severe" on EPA's ozone nonattainment list. "The air is getting worse, not better," says Paul Templet, professor of environmental studies at Louisiana State University, Baton Rouge, and 1988-92 head of Louisiana's Dept. of Environmental Quality. The dialogue between industry and environmentalists, he adds, "is nonexistent." The Baton Rouge area is a focus of the nationwide "environmental justice" controversy, in which environmental groups are challenging environmental operating permits of industrial facilities in economically disadvantaged areas that have heavy minority populations. Environmental problems aren't limited to U.S. metro areas. Pollution has become severe enough in Paris, for instance, that authorities -- following the example of Milan, Italy, and Athens, Greece -- permit citizens to drive their cars only on alternate days. In Germany, where the "green" movement has political-party status, former East German cities -- notably Leipzig -- are rife with air- and water-quality problems. Metro areas in developing nations, however, suffer from even worse pollution. In a January study, the World Resources Institute, a Washington, D.C.-based environmental research group, and the World Health Organization, a United Nations unit, ranked major international cities for their concentrations of harmful air pollutants to children under age five. The 10 worst offenders -- all in developing economies -- in order are: Mexico City, Beijing, Shanghai, Teheran, Calcutta, Mumbai (Bombay), Delhi, Tianjin, Manila, and So Paulo.