No abstract

Light-duty vehicle emissions were measured at the Caldecott Tunnel in August and October 1994. In the interval between these two periods, the average oxygen content of gasoline sold in the San Francisco Bay area increased from 0.3 to 2.0% by weight. Compared to the August (low-oxygenate) sampling period, measured pollutant emission rates during the October (high-oxygenate) sampling period for CO and VOC decreased by 21 ( 7 and 18 ( 10%, respectively, while NO x emissions showed no significant change. Formaldehyde emissions increased by 13 ( 6%, acetaldehyde emissions did not change significantly, and benzene emissions decreased by 25 ( 17%. Speciated VOC emission profiles show that the use of oxygenated gasoline resulted in higher MTBE and lower aromatic hydrocarbon emissions, higher isobutene, and lower aromatic aldehydes. The normalized reactivity of NMOG emissions did not change significantly between the low-oxygenate and highoxygenate sampling periods. VOC exhaust speciation profiles for vehicles operating in the hot-stabilized mode at the Caldecott Tunnel match the speciation profile for cold-start emissions from new vehicles as measured in the Auto/Oil program. California's motor vehicle emission factor model, EMFAC7F, accurately predicts the VOC/NO x ratio measured at the Caldecott Tunnel in August, but underpredicts the observed CO/NO x ratio by a factor of 1.5-2.2 over the range of vehicle speeds observed at the tunnel.

This paper addresses the impact of California phase 2 reformulated gasoline (RFG) on the composition and reactivity of motor vehicle exhaust and evaporative emissions. Significant changes to gasoline properties that occurred in the first half of 1996 included an increase in oxygen content; decreases in alkene, aromatic, benzene, and sulfur contents; and modified distillation properties. Vehicle emissions were measured in a San Francisco Bay Area roadway tunnel in summers 1994-1997; gasoline samples were collected from local service stations in summers 1995 and 1996. Equilibrium gasoline headspace vapor composition was calculated from measured liquid gasoline composition. Addition of methyl tert-butyl ether (MTBE) and reduction of alkenes and aromatics in gasoline between summers 1995 and 1996 led to corresponding changes in the composition of gasoline headspace vapors. Normalized reactivity of liquid gasoline and headspace vapors decreased by 23 and 19%, respectively. Ozone formation should be reduced because of both lower gasoline vapor pressure, which leads to lower mass emissions, and reduced reactivity of gasoline vapors. The reactivity of onroad emissions measured in the tunnel decreased by 8% or less. The reduction in reactivity of on-road emissions was less than that of evaporative emissions because of increased weight fractions of highly-reactive isobutene and formaldehyde in vehicle exhaust, which resulted from the increased use of MTBE in gasoline. On-road vehicle emissions of volatile organic compounds in the tunnel appear to be dominated by vehicles that have reduced catalytic converter activity.

Ammonia is the primary alkaline gas in the atmosphere and contributes to fine particle mass, visibility problems, and dry and wet deposition. The objective of this research was to measure ammonia and other exhaust emissions from a large sample of on-road vehicles using California phase 2 reformulated gasoline with low sulfur content (∼10 ppm by weight). Vehicle emissions of ammonia, NO x , CO, and CO 2 were measured in the center bore of a San Francisco Bay area highway tunnel on eight 2-h afternoon sampling periods during summer 1999. Ammonia concentrations were divided by total carbon (mainly CO 2 ) concentrations to compute an emission factor of 475 ( 29 mg L -1 (95% C.I.). The molar ratio of nitrogen emitted in the tunnel in the form of ammonia to that emitted in the form of NO x was 0.27 ( 0.01. Emissions of NO x and CO have been measured at this tunnel sampling location since 1994. From 1994 to 1999, emissions decreased by 41 ( 4% for NO x and 54 ( 6% for CO. These reductions include the impacts of turnover in the vehicle fleet and the use of reformulated gasoline. Between 1997 and 1999, when fuel properties did not change significantly, emissions of NO x and CO decreased by 26 ( 2% and 31 ( 3%, respectively. While use of three-way catalytic converters has contributed to decreases in NO x and CO emissions, their use, in combination with fuel-rich engine operation, is the likely cause of the ammonia emissions from motor vehicles observed during this study.

This paper addresses the impact of California phase 2 reformulated gasoline (RFG) on motor vehicle emissions. Phase 2 RFG was introduced in the San Francisco Bay Area in the first half of 1996, resulting in large changes to gasoline composition. Oxygen content increased from 0.2 to 2.0 wt%; and alkene, aromatic, benzene, and sulfur contents decreased. Gasoline density and T 50 and T 90 distillation temperatures also decreased. Light-duty vehicle emission rates were measured in a Bay Area roadway tunnel in summers 1994−1997. Vehicle speeds and driving conditions inside the tunnel were similar each year. The average model year of the vehicle fleet was about one year newer each successive summer. Large reductions in pollutant emissions were measured in the tunnel over the course of this study, due to a combination of RFG and fleet turnover effects. Between summers 1994 and 1997, emissions of carbon monoxide decreased by 31 ± 5%, non-methane volatile organic compounds (VOC) decreased by 43 ± 8%, and nitrogen oxides (NO x ) decreased by 18 ± 4%. It was difficult to separate clearly the fleet turnover and RFG contributions to these changes. Nevertheless, it was clear that the effect of RFG was greater for VOC than for NO x . The RFG effect on vehicle emissions of benzene was estimated to be a 30−40% reduction. Use of RFG increased formaldehyde emissions by about 10%, while acetaldehyde emissions did not change significantly. RFG effects reported here may not be the same for other driving conditions or for other vehicle fleets. RFG effects on evaporative emissions are also important. The combined effect of phases 1 and 2 of California's RFG program was a 20% reduction in gasoline vapor pressure, about one-fifth of which occurred following the introduction of phase 2 RFG.