While automakers like Mercedes-Benz, Volkswagen and others already sell diesel engines in popular car models, the news that BMW will join that group is still noteworthy. By adding urea — an additive that cuts certain pollutants by 50 – 90% when used in heavy-duty vehicles — BMW will meet stringent U.S. standards in all 50 states. Currently, California’s even tougher emission standards exclude even the most modern diesel cars from being sold there. There’s no word on how the urea will be added to the diesel fuel or which BMW models will feature the diesel option. But BMW says it will figure it all out in less than two years.