Emission Control and Air Pollution Module

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A Summary of Some Specific Clean Air Act Programs

Tighter Tailpipe Standards

Tailpipe (exhaust) standards for cars have been reduced under the 1990 law. The previous standards of 0.41 gram per mile (gpm) total hydrocarbons, 3.4 gpm carbon monoxide, and 1.0 gpm nitrogen oxides have been replaced with standards of 0.25 gpm nonmethane hydrocarbons and 0.4 gpm nitrogen oxides (the 3.4 gpm standard for carbon monoxide does not change). These standards will be fully phased in with 1996 models. EPA is required to study whether even tighter standards are needed, technologically feasible, and economical. If EPA determines by 1999 that lower standards are warranted, the standards will be cut in half beginning with 2004 model year vehicles.

Carbon Monoxide Control

Mobile sources are the primary cause of carbon monoxide pollution in the United States. The 1990 Clean Air Act sets up two programs to address this problem. For the first time, carbon monoxide emissions will be regulated at cold temperatures. Carbon monoxide emissions can be very high in cold weather because both fuel combustion and pollution control equipment operate less efficiently in the cold. In the past, tailpipe standards applied only at 75 °F. so manufacturers optimized emission control equipment for that temperature. The 1990 Clean Air Act requires cars to meet a carbon monoxide standard at 20 °F. The phase-in of a 10 gpm standard began with 1994 models. If, by 1997, carbon monoxide levels are still too high in six or more cities, the cold temperature emission standard will drop to 3.4 gpm for 2002 models. The second new provision involves increasing the oxygen content of gasoline sold during the winter in cities that exceed national air quality standards for carbon monoxide pollution. The oxygen helps reduce carbon monoxide emissions by enhancing fuel combustion. 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.

Air Toxins Control

Most provisions requiring cleaner cars and fuels will dramatically lower vehicle toxic emissions. In addition, EPA has completed a study of air toxins emissions and may, if warranted, regulate emissions of benzene, formaldehyde, and other toxic air pollutants.

Reformulated Gasoline

By 1995, all gasoline sold in the country's worst ozone areas must contain a minimum oxygen content and a maximum benzene content. Through refining changes that will not be apparent to motorists, reformulated gasoline will achieve a 15 to 17 percent reduction in both ozone forming hydrocarbons and toxic emissions from motor vehicles. By 2000, gasoline sold in these cities will achieve a 25 to 29 percent hydrocarbon reduction, a 20 to 22 percent toxins reduction, and a 9 to 10 percent reduction in nitrogen oxide emissions. Many cities have voluntarily chosen to use this cleaner gasoline.

Urban Buses

Beginning in 1993, the diesel particulate standard for urban buses was reduced by 60 percent, from 0.25 to 0.1 gram per brake-horsepower per hour (g/bhp-hr). The standard, which applies to urban transit buses, dropped to 0.07 g/bhp-hr in 1994 and to 0.05 g/bhp-hr in 1996. If monitoring data show that buses in actual use are not meeting the standard, EPA must implement a "low-polluting fuels" program for new buses in large cities. Possible fuels include methanol, ethanol and compressed natural gas.

Clean Fleets

Beginning in 1998, 30 percent of new vehicles purchased by centrally-fueled fleets in certain cities will be required to use clean fuels and meet tailpipe standards that are lower than those in place for general passenger cars (0.075 gpm hydrocarbons, 3.4 gpm carbon monoxide, and 0.2 gram per mile nitrogen oxides). The purchase requirement will grow to 70 percent by the year 2000. The program, which is intended to stimulate development of new, low-polluting fuel/vehicle combinations, will affect 22 metropolitan areas in 19 states across the country where pollution levels are high.

California Pilot Program

Like the fleets program, the California Pilot program is designed to encourage production of clean fuels and vehicles. Beginning in 1996, manufacturers must produce at least 150,000 "clean" cars (capable of meeting a 0.125 gpm hydrocarbon, 3.4 gpm carbon monoxide, and 0.4 gpm nitrogen oxide standard) for sale in California. The number increases to 300,000 by the year 1999. In 2001, the standards drop to the fleets program levels. Other states may petition EPA to adopt this program.