<Li> Inefficient catalytic converter under cold conditions: Catalytic converters are very inefficient until up to their operating temperature . This time has been much reduced by moving the converter closer to the exhaust manifold and even more so placing a small yet quick - to - heat - up converter directly at the exhaust manifold . The small converter handles the start - up emissions, which allows enough time for the larger main converter to heat up . Further improvements can be realised in many ways, including electric heating, thermal battery, chemical reaction preheating, flame heating and superinsulation . </Li> <Table> U.S. Environmental Protection Agency estimates of average passenger car emissions in the United States for April 2000 <Tr> <Th> Component </Th> <Th> Emission Rate </Th> <Th> Annual pollution emitted </Th> </Tr> <Tr> <Td> Hydrocarbons </Td> <Td> 2.80 grams / mile (1.75 g / km) </Td> <Td> 77.1 pounds (35.0 kg) </Td> </Tr> <Tr> <Td> Carbon monoxide </Td> <Td> 20.9 grams / mile (13.06 g / km) </Td> <Td> 575 pounds (261 kg) </Td> </Tr> <Tr> <Td> NO </Td> <Td> 1.39 grams / mile (0.87 g / km) </Td> <Td> 38.2 pounds (17.3 kg) </Td> </Tr> <Tr> <Td> Carbon dioxide - greenhouse gas </Td> <Td> 415 grams / mile (258 g / km) </Td> <Td> 11,450 pounds (5,190 kg) </Td> </Tr> </Table> <Tr> <Th> Component </Th> <Th> Emission Rate </Th> <Th> Annual pollution emitted </Th> </Tr> <Tr> <Td> Hydrocarbons </Td> <Td> 2.80 grams / mile (1.75 g / km) </Td> <Td> 77.1 pounds (35.0 kg) </Td> </Tr>

What gas comes out of a car exhaust