On April 4, the American Petroleum Institute released its report “Effects of Light-duty Vehicle Emissions Standards and Gasoline Sulfur Level on Ambient Ozone,” prepared by ENVIRON International Corporation. The report said the Tier 3 proposed rule, which would reduce the amount of sulfur in gasoline from 30 parts per million to 10ppm, would reduce ozone levels by less than 1 percent. The API said the Tier 3 rule will have marginal benefits compared to Tier 2 which lowered sulfur concentrations in gasoline from 300ppm to 30ppm.