By Norman Fichthorn (October 18, 2018, 2:43 PM EDT) -- The phrase "interstate transport" may conjure images of planes, trains and trucks carrying people and goods cross-country. But, under the federal Clean Air Act, or CAA, the term is often used to refer to interstate air pollution — emissions from factories, power plants, motor vehicles, refineries and other sources that are transported by prevailing winds across state lines, sometimes over hundreds of miles. The interstate transport phenomenon often has posed for the U.S. Environmental Protection Agency what the U.S. Supreme Court has called "a thorny causation problem: How should EPA allocate among multiple contributing upwind States responsibility for a downwind State's excess pollution?"[1]...