The air inside school buses can contain dangerous levels of cancer-causing soot, according to a study released this week by the Natural Resources Defense Council, the Coalition for Clean Air, and scientists at the University of California at Berkeley. The levels of diesel exhaust on the buses were up to 8.5 times higher than the average levels found in California’s smoggy air. Soot concentrations more than doubled when windows were closed. The study estimates that from 23 to 46 children out of every 1 million who ride a school bus will someday get cancer as a result of their exposure to diesel exhaust.