Two coal-fired electric power plants in Mexico, Carbon I and Carbon II, in Coahuila, about 125 miles southeast of Big Bend, are suspected as significant sources. A Texas Center for Policy Studies report estimated that sulfur dioxide emissions from the Mexican plants could reach 250,000 tons per year. Texas power plants contribute, too. Sulfur dioxide emissions from plants in southern, eastern and central Texas total 770,000 tons per year, the Texas research center said. Wind patterns from the Gulf Coast, Mexico and eastern Texas play a role in the park's problem.
Reduced visibility is caused largely by fine sulfur particles that create a white haze.
But critics say that figure is dubious. Jim Marston, who heads the Texas office of the Environmental Defense Fund, contends that air pollution has been lowered by less than a third of 1 percent. But Mexico backed out last year. Texas' visibility plan comes under review every three years, and the EPA has been studying it for the past six months, said Jim Yarbrough, EPA environmental scientist in Dallas. Ramon Alvarez of the Environmental Defense Fund believes the United States and Texas have used Mexico's role as an excuse for their lack of action.