The wintertime fuel requirements began in 1992. Ozone Control Ground-level ozone, a primary component of smog, exceeds healthy levels in cities across the United States. It is our most serious and persistent air quality problem. A major thrust of the 1990 Clean Air Act involves reducing urban ozone levels. As a complement to stricter tailpipe standards, the new law introduces several programs to minimize pollution from evaporating gasoline.
Evaporative emissions are a major source of the hydrocarbon compounds that form ground-level ozone.
Devices that trap gasoline vapors from the engine and fuel system will be improved. In addition, gasoline volatility will be capped, reducing the propensity for gasoline to evaporate in the first place. Most provisions requiring cleaner cars and fuels will dramatically lower vehicle toxic emissions. In addition, EPA has completed a study of air toxics emissions and may, if warranted, regulate emissions of benzene, formaldehyde, and other toxic air pollutants. By 1995, all gasoline sold in the country's worst ozone areas must contain a minimum oxygen content and a maximum benzene content.