Impact of California Reformulated Gasoline on Motor Vehicle Emissions. 2. Volatile Organic Compound Speciation and Reactivity

Abstract

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.

Summer and Winter Nonmethane Hydrocarbon Emissions from On-Road Motor Vehicles in the Midwestern United States

“…Fuel headspace has been seen to account for 10 -15% of emissions in other tunnel studies, 14,22 and unreacted gasoline has been seen to contribute up to or more than half of total emitted NMHC mass. 8,14,23 The higher proportion of alkanes in the summer Kilborn tunnel tests is consistent with headspace or evaporative emissions. Compared with summer gasoline, summer Kilborn tunnel tests were depleted in aromatics, and enriched in n-alkanes, n-alkenes, branched alkenes, and cycloalkanes, shifts that indicate impacts of both headspace and partial combustion of fuel.…”

“…Emissions of carbonyl compounds from motor vehicles have been reported by others for tests conducted in tunnels. 3,7,8 However, in the present study, analysis of duplicate samples indicated that measurement uncertainty for these compounds was large, and, thus, our measurements were not statistically significant. To sample volatile ammonia concentrations, oxalicacid coated, prebaked quartz fiber filters were used downstream of PM filters.…”

“…All NMHC samples collected in tunnel tests (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and parking garage test (PG). Comparison between the collocated sample measurements from each laboratory was used to validate the data.…”

Unspeciated organic emissions from combustion sources and their influence on the secondary organic aerosol budget in the United States

“…For example, Fig. 3 indicates that current inventories have essentially no emissions of unspeciated organics for on-road gasoline sources, which stands in contrast to the data presented here and in the literature (16,17,29,(34)(35)(36)(37).…”

An Assessment of the Impact of California's Phase 2 Reformulated Gasoline on Ozone Air Quality

“…However, an assessment of the reactivity of the total emissions from gasoline-powered vehicles before and after CaRFG indicates that reactivity declined with the introduction of CaRFG. 15,16 Because our analyses disregarded reactivity, we should tend to understate the effectiveness of CaRFG in reducing ozone. The inventory we used included estimates of mobile source emissions that were based on MVEI7G.…”