A global inventory of carbon monoxide emissions from motor vehicles

Automobile emissions are the major urban source of carbon monoxide, and they are also important globally. One estimate by the Japanese Automobile Research Institute (JARI) of the 1990 global CO emissions from automobiles is 231 megatonnes (Mt). The same source gives the USA 1990 emissions as 21 Mt, whereas the US Environmental Protection Agency (EPA) estimate 57 Mt. The two sources agree that the mobile source (including airplanes) CO2 emissions are about 1500 Mt. Thus the disagreement is in the CO/CO2 molar ratio (JARI 0.022, EPA 0.062). We have developed a device which measures the CO/CO2 ratio in the exhaust of motor vehicles passing in a single lane. At busy locations we measure over 1000 vehicles per hour. Over the last 10 yrs these ratios have been measured from over ten million vehicles in eighteen countries. The results can be directly converted into mass of emissions per liter of fuel burned. On-road CO emissions depend on the vehicle technology, its state of maintenance, and thus upon fleet age. Our estimate of the 1991 global CO emissions from motor vehicles is 213 Mt, of which 88% (188 Mt) were produced in the northern hemisphere, with 17% (36 Mt) produced in the USA. This estimate for USA 1991 emissions is intermediate between the JARI and EPA 1990 estimates. For 1995 relative to 1991, we estimate a 17% decrease in global CO emissions from motor vehicles, arising from fleet emissions technology upgrades, somewhat countered by increased fuel consumption.