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Cold operating environment has many kinds of negative effects on the use of automobiles. Low ambient temperature degrades start-up performance and increases fuel consumption. Hence, the amounts of exhaust emissions are also elevated. In particular, high concentrations of CO and HC are present in the exhaust. Cold-start derates especially the performance of a TWC type of emission reduction. Therefore, an increasing emphasis has been set to the testing of exhaust emissions even at sub-ambient temperatures, For this reason, US-EPA has recently revised US emission regulations by comprising an additional low ambient temperature (20°F = -7°C) test for CO emissions. Apart from the regulated components, other poisonous compounds have been detected from the exhausts, although usually in very small quantities, A cold-start may have an increasingly strong effect even to the emission of these substances.

Cold operating environment has many kinds of negative effects on the use of automobiles. Low ambient temperature degrades start-up performance and increases fuel consumption. Hence, the amount of harmful exhaust emissions is also elevated. In particular, high concentrations of carbon monoxide (CO) and unburned hydrocarbons (HC) are present. The continuously widening implementation of US-type emission regulations around the world has brought emission control technology based on the use of three-way catalyst (TWC) even to the Nordic countries having cold climate. Cold-start increases emissions from conventional cars, and especially the performance of TWC type of emission reduction has been shown to be quite susceptible to low ambient temperature. Therefore, an increasing emphasis has been set to the testing of exhaust emissions also at sub-normal temperatures, i.e. below the range of +20 …+30°C widely designated by the legislative procedures.