A fuel-based inventory of motor vehicle exhaust emissions in the Los Angeles area during Summer 1997

A fuel-based approach was used to estimate stabilized exhaust carbon monoxide (CO) and volatile organic compound (VOC) emissions in California's South Coast Air Basin (SoCAB). Fleet-average emission factors of 80±7 g l⁻¹ CO and 9.3±1.5 g l⁻¹ VOC were calculated from more than 60,000 infrared remote sensor measurements collected at 35 sites throughout the greater Los Angeles area during summer 1997. Fuel use by SoCAB cars and light/medium-duty trucks was estimated to be 5.9±0.3×10⁷ l day⁻¹ based on statewide gasoline sales during summer 1997. Fuel-based estimates of 4700±500 metric tons day⁻¹ CO and 550±90 metric tons day⁻¹ VOC are higher than stabilized exhaust emissions estimates of California's MVEI 7G model by factors of 2.4±0.2 for CO and 3.5±0.6 for VOC. According to fuel-based inventory estimates, stabilized CO emissions in 1997 were lower by 20% than emissions during summer 1991. Fuel use increased by 8% during this period while the CO emission factor decreased by 26%. The relationship between income level and vehicle emissions was examined using census data resolved to the zip code level. On average, CO and VOC emission factors of vehicles registered in the lowest income areas were double those of vehicles registered in the highest income areas. Differences in vehicle emissions between neighborhoods were due in part to differences in the prevalence of older vehicles, but also resulted because vehicles of the same age had higher emissions in lower-income areas.