Greenwire: The Obama administration is in the midst of a landmark series of Clean Air Act rulemakings. In 18 months, U.S. EPA has — among other things — stiffened standards for sulfur dioxide and nitrogen dioxide for the first time in decades, revamped the George W. Bush administration’s smog regulations and issued the first climate rules under the Clean Air Act. And that is just the beginning. EPA is expected to lay out additional plans for the Clean Air Act today as it marks the …