An independent research firm's review of industry statistics compiled by the federal government shows that emissions from the U.S. refineries have plummeted over the past two decades, according a report by Sage Environmental Consulting for the American Fuel & Petrochemical Manufacturers (AFPM). In "Historical Air Emissions from the U.S. Petroleum Refineries," Sage researchers said refinery emissions of sulfur dioxide, nitrogen oxides and volatile organic compounds dropped by 91%, 67% and 69%, respectively, between 1990 and 2013. AFPM cited the survey results as a reason the U.S. Environmental Protection Agency (EPA) does not need to change the existing ozone limit from 75 parts-per-billion (ppb) to 65-70 ppb.