Exhaust Emission Levels of In-Service Vehicles - Comparison of 1970 and 1971 Surveys

The results of a nationwide automobile exhaust emission survey conducted in 1971 are presented and compared to data obtained from a 1970 survey. Average hydrocarbon and carbon monoxide emissions are given for engine speeds of idle and 2500 rpm.

Vehicle distribution curves for hydrocarbon and carbon monoxide emissions are shown for the 1971 data for selected year groups based on emission control devices. Comparison of the distribution curves obtained from the 1971 and 1970 data show that “deterioration” (increased emissions) occurred at both idle and 2500 rpm in the one year period. The effects of carburetor adjustments on idle emissions are compared for the 1971 and 1970 data.