During the first few minutes of driving, a cold started passenger car, will sustain increased fuel consumption and elevated emissions of toxic substances with the exhaust gases. "Start emissions" of regulated substances, due to the cold start phase, were calculated from emission data published by official Swedish sources, for passenger cars with, as well as without, three-way catalyst (TWC). A survey of how quantities of emitted pollutants vary with temperature revealed substantial increases in start emissions of hydrocarbons and carbon monoxide resulting from cold start at low ambient temperatures, but no corresponding effect pertaining to nitrogen oxides. The HC and CO start emissions values, calculated for cars with three-way catalyst, were found to amount to one half and one third respectively of the corresponding values for older non-catalyst cars. These rather small quotients prove new cars to be virtually devoid of exhaust emission control during the cold start phase. A principal result from the study is the fact that start emissions of nitrogen oxides for old non-catalyst cars were less than 0.5 grams of NOx. Hitherto, values of between 4 and 5 g NOx have been prevalent. (A)
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