Vehicles and the Emissions They Produce

What Has Been Done to Control Automobile Emissions?

Simply put—a lot. The original Clean Air Act of 1970 gave the U.S. EPA broad authority to regulate motor vehicle pollution, and the Agency’s emission control policies and requirements have become progressively more stringent since then.

EPA standards dictate how much pollution autos may emit per mile they are driven, and automotive engineers and scientists decide how best to achieve these limits. For example, the emission reductions of the 1970’s were achieved because of fundamental improvements in engine design, plus the addition of charcoal canisters to collect hydrocarbon vapors and exhaust gas recirculation valves to reduce nitrogen oxides.

The advent of “first generation” catalytic converters (or "catalysts") in 1975 significantly reduced hydrocarbon and carbon monoxide emissions. The use of converters provided a huge indirect benefit as well. At the time, gasoline contained lead ("leaded fuel") that reduced the effectiveness of catalysts, and as a result 1975 also saw the widespread introduction of "unleaded" gasoline. This resulted in dramatic reductions in ambient lead levels and alleviated many serious environmental and human health concerns associated with lead pollution.

The next major milestone in vehicle emission control technology came in 1980 and 1981. In response to tighter standards, manufacturers equipped new cars with even more sophisticated emission control systems. These systems generally included “three-way” catalyst (which converts carbon monoxide and hydrocarbons to carbon dioxide and water, and also helps change nitrogen oxides to elemental nitrogen and oxygen) plus the introduction of on-board computers, systems to better control fuel, and oxygen sensors. This equipment helped to further optimize the efficiency of the catalytic converter.

The 1990 Clean Air Act required manufacturers to further reduce vehicle tailpipe and evaporative emissions and to increase emissions control system durability. These requirements led to the use of more sophisticated on-board computers, widespread use of electronic fuel control, and new computerized diagnostic systems to notify drivers when an emissions control system may be malfunctioning.

Starting in 2004, vehicles emissions are again being reduced in compliance to EPA's Tier 2 emission standards. These standards require that all new vehicles achieve a 96-99% reduction (from pre-emissions control levels) in hydrocarbon, carbon monoxide and nitrogen oxide emissions, effectively eliminating almost all pollutants from today's vehicles.