Tier 3 requires the oil industry to reduce the sulfur level in gasoline by more than 60 percent, to just 10 parts per million (ppm) in 2017. It's currently 30 ppm. Cleaner gasoline will mean that ...

Currently, gasoline and new cars meet Tier 2 standards that were implemented from 2000 to 2007 and resulted in a nearly 10-fold reduction in sulfur and cut tailpipe emissions of nitrogen oxides by ...