SIOUX CITY— Sioux City-based Terra Industries has agreed to pay $625,000 in civil penalties to settle alleged violations of the federal Clean Air Act and spend $17 million to install pollution controls at plants in Iowa, Mississippi and Oklahoma. Terra, one of the nation’s largest producers of nitric acid and nitrogen fertilizers, will pay $325,000 to the federal government and $100,000 each to environmental agencies in Iowa, Mississippi and Oklahoma. Those agencies were co-plaintiffs in an action filed Tuesday in U.S. District Court in Sioux City. Terra says in a statement that it worked with the U.S. Environmental Protection Agency to reach a settlement and develop plans to implement emissions reduction initiatives. The company says that by doing so it isn’t admitting any violation of law or regulation.