A Fuel-Based Approach to Estimating Motor Vehicle Cold-Start Emissions

摘要

The temporary ineffectiveness of motor vehicle emission controls at startup causes emission rates to be much higher for a short period after starting than during fully warmed, or stabilized, vehicle operation. Official motor vehicle emission inventories estimate that excess emissions dur- ing cold-start operation contribute a significant fraction of all hydrocarbon, carbon monoxide (CO), and nitrogen oxide (NOx) emissions from California vehicles. In an ef- fort to verify these estimates under real-world conditions, vehicle emissions were measured in an underground park- ing garage in Oakland, CA, during March 1997. Hot sta- bilized emissions were measured as vehicles arrived at the garage in the morning, and cold-start emissions were measured as vehicles exited in the afternoon; the incre- mental, or excess, emissions associated with vehicle start- ing were calculated by difference. Composite emissions from ~135 vehicles were sampled during each of six morn- ing and six afternoon periods. Measured stabilized exhaust emissions were 19 ± 2 g nonmethane hydrocarbons (NMHC), 223 ± 17 g CO, and 8.6 ± 1.3 g NOx per gal of gasoline consumed. Cold-start emissions of 69 ± 2 g NMHC/gal, 660 ± 15 g CO/gal, and 27.8 ± 1.2 g NOx/gal were measured for vehicles spending an average of ~60 sec in the garage after starting in the afternoon. Using second-by-second emissions data from California's light- duty vehicle surveillance program, average fuel use dur- ing cold start was estimated to be ~0.07 gal, and the cold- start period was estimated to last for ~200 sec. When cold- start e