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Industries that rely on mechanical processes include metal smelters, grain elevators, foundries,
steel manufacturers, wood processors, cotton gins, asphalt-batching operations, concrete- and cement-batching operations, paper mills, sandblasting operations, and oil and gas rigs. These
industries are another major category of stationary sources that can pollute the air. Operation of cotton gins, for example, may result in large emissions of particulate matter. In 1990 air
sampled around a cotton gin in the Lower Rio Grande Valley showed that respirable particulate matter was being emitted at high levels, although not in violation of standards applicable to
agricultural sources.* Lead smelters are of particular concern to citizens living near them and to environmental groups. As an air pollutant, lead is emitted in particles so small that 50 percent might remain in the lungs if breathed by humans.* However, tests conducted by the Texas Air Control Board in response to citizen complaints found that levels of lead in the ambient air near smelters in San Antonio, Garland, and Dallas were below national air quality standards.* Any lead smelters built after 1987 must be at least 3,000 feet from the nearest residence.*
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