A Phelps Dodge smelter poured its final copper.

The firm’s plant in Douglas, Ariz., is being shut down because pollution controls would be too costly to install. The shutdown spelled an end to white-gray clouds of smoke containing sulfur dioxide and other pollutants spewing from twin stacks that drifted across Arizona, New Mexico and Colorado, and even into northern Mexico when the wind was right. The company said installation of pollution controls would cost too much and opted to shut down instead after heavy pressure from environmentalists, then-Arizona Gov. Bruce Babbitt and the federal Environmental Protection Agency.