The U.S. Supreme Court today let stand federal rules intended to reduce the amount of smog drifting across state borders from smokestacks in the Midwest and South to the Northeast. In 1998, the U.S. EPA required 22 states and the District of Columbia to submit plans to cut nitrogen oxide pollution, placing a heavier burden for emissions reductions on the states where the pollution originated. Seven of those states, including Michigan and Ohio, and about 50 power companies challenged the plan, saying the EPA exceeded its authority in setting the rules and wrongly based them on minimizing the costs of reducing the pollution. The court rejected the challenge without comment.