Issues and responses
With Japan's economic prosperity of the 1960s, air pollution in large cities became a serious problem. Motor vehicle manufacturing supported the development of industry and improvements in living standards, but automobiles also emitted large amounts of exhaust gases. The auto industry very quickly began research on the reduction of exhaust emissions and by 1978 was able to fully comply with the government's new emission regulations--the most stringent in the world. Confronted now with the urgent problem of global warming and other pressing issues, auto manufacturers today are making every effort to achieve further reductions in vehicle exhaust emissions.

Gasoline engines
Emissions from gasoline engines include such harmful elements as carbon monoxide (CO), hydrocarbons (HC) and NOx. The level of these harmful elements in the air can be reduced by decreasing exhaust emissions from vehicle engines and by treating those emissions to reduce their toxicity. Most cars running on gasoline now use three-way catalytic converters which enable simultaneous oxidization and deoxidization in order to treat all three harmful elements at the same time. NOx-occluding deoxidization-type three-way catalytic converters which treat the NOx emitted by lean-burn engines have also been developed.

Diesel engines
Diesel engines provide such advantages as low fuel consumption and excellent durability, but they also emit large amounts of NOx and particulate matter. Furthermore, certain diesel-related problems are not easy to resolve; for example, three-way catalytic converters cannot be used with diesel engines. In recent years, however, NOx emissions from diesel engines have been decreasing thanks to improvements in combustion chambers, high-pressure fuel injection, EGR (exhaust gas recirculation) systems and electronic fuel-injection systems. In addition, engines equipped with a completely new type of electronically-controlled fuel-injection system called "common rail" should reduce NOx and PM emissions significantly.