The wheels on the bus go round and round, and the diesel fumes from the bus go far and wide. That’s the bad news from a study released yesterday by the Union of Concerned Scientists analyzing emissions from the nation’s 454,000 school buses. Nine out of 10 of those buses are powered by diesel fuel, which can increase risk of cancer and exacerbate or cause asthma. The study also ranked every state by school bus emissions; California and Washington tied for worst, each receiving a “D.” On average, every bus in the Golden State emits the same amount of particulates in a year as 170 cars. The report recommended converting buses to run on natural gas in order to reduce emissions and related health threats.