Acid deposition, smelter emissions, and the linearity issue in the Western United States.

The variation in sulfur dioxide emissions from nonferrous metal smelters in the western United States over a 4-year period is compared with the variation in sulfate concentrations in precipitation in the Rocky Mountain states. The data support a linear relation between emissions and sulfate concentration. The geographic separation of emissions sources and precipitation monitors indicates a sulfur transport scale exceeding 1000 kilometers.