EMISSION STANDARDS

The vehicle emission standards were implemented for the first time in 1965 when control of crankcase hydrocarbon emissions from gasoline passenger cars was required as per the law. Use of positive crankcase ventilation (PCV) system on the gasoline passenger cars became necessary to prevent emission of hydrocarbon rich crankcase blow by gases into atmosphere. At the same time, the exhaust gas emission standards for new cars were also established in the state of California and in 1968, US enacted legislation to implement nationwide vehicle emission regulations. In Europe , vehicle emission standards were implemented beginning from the year 1970. Over the years, the emission standards have become more and more stringent and have driven the development of advanced engine designs and emission control technology. Now, nearly all the countries all over the world have enforced vehicle emission regulations of varying severity following largely either the US or the European regulations.The emission limits that are in force in the US and Europe and the trends thereof over the years are discussed below.

Light Duty Vehicles

US Standards

The US emission standards for passenger cars are given in Table 4.1 since the limits were set for the first time under the Clean Air Act of 1968. The standards set for 1975 were rather stringent such that the oxidation catalytic converters were required on most cars. Amendments to Clean Air Act in 1977 resulted in the standards that required in 1980/1981 reduction of 90% in HC and CO, and 75% in NO_x . The 1980-81 standards resulted in widespread use of 3-way catalyst technology.

During 1990s, the 1977 amendments were found inadequate as 9 US cities had higher ozone levels and 41 cities higher CO levels than the air quality standards. The 1990 Clean Air Act Amendments (CAAA) followed resulting in further tightening of the emission standards besides other measures like introduction of better quality fuels such as the reformulated gasoline. The new emission regulations known as Tier 1 were implemented from 1994 and Tier 2 standards from 2004 through to 2009. It is seen that the current production vehicles emit less than 1% of emissions of pre-control era vehicles.