Effects of Reformulated Gasoline and Motor Vehicle Fleet Turnover on Emissions and Ambient Concentrations of Benzene

Abstract

Gasoline-powered motor vehicles are a major source of toxic air contaminants such as benzene. Emissions from light-duty vehicles were measured in a San Francisco area highway tunnel during summers 1991, 1994-1997, 1999, 2001, and 2004. Benzene emission rates decreased over this time period, with a large (54 +/- 5%) decrease observed between 1995 and 1996 when California phase 2 reformulated gasoline (RFG) was introduced. We attribute this one-year change in benzene mainly to RFG effects: 36% from lower aromatics in gasoline that led to a lower benzene mass fraction in vehicle emissions, 14% due to RFG effects on total nonmethane organic compound mass emissions, and the remaining 4% due to fleet turnover. Fleet turnover effects accumulate over longer time periods: between 1995 and 2004, fleet turnover led to a 32% reduction in the benzene emission rate. A approximately 4 microg m(-3) decrease in benzene concentrations was observed at a network of ambient air sampling sites in the San Francisco Bay area between the late 1980s and 2004. The largest decrease in annual average ambient benzene concentrations (1.5 +/- 0.7 microg m(-3) or 42 +/- 19%) was observed between 1995 and 1996. The reduction in ambient benzene between spring/summer months of 1995 and 1996 due to phase 2 RFG was larger (60 +/- 20%). Effects of fuel changes on benzene during fall/winter months are difficult to quantify because some wintertime fuel changes had already occurred prior to 1995.

Multi-year (2004–2008) record of nonmethane hydrocarbons and halocarbons in New England: seasonal variations and regional sources

“…9b). This ratio value is indicative of a vehicular source and is consistent with observations of ambient benzene/ethyne ratios measured during several spring-summer field campaigns conducted throughout the US (Fortin et al, 2005;Harley et al, 2006;Parrish, 2006;Sistla and Aleksic, 2007;Warneke et al, 2007) and in major cities . The strong correlations between propane and ethyne (Fig.…”

On the observed response of ozone to NO<sub>x</sub> and VOC reactivity reductions in San Joaquin Valley California 1995–present

“…VOC emissions from mobile sources have been thought to be largest source of O 3 forming organic precursors in the Valley (Hu et al, 2012). Regulatory efforts during our study window have focused on VOC emissions from light-duty vehicles and reduced these emissions through a combination of stricter standards and gasoline reformulation (Kirchstetter et al, 1999;Harley et al, 2006). At high temperatures in the Central and Northern SJV, we also show that reductions in VOCR have significantly decreased the frequency of violations.…”

On the temperature dependence of organic reactivity, nitrogen oxides, ozone production, and the impact of emission controls in San Joaquin Valley, California

“…In light of the CalNex-SJV i VOCR i and VOCR observations and well-documented efforts to control motor vehicle emissions (e.g., Kirchstetter et al, 1999a, b;Parrish et al, 2002;Harley et al, 2006;Parrish, 2006;Bishop and Stedman, 2008) we speculate that it is the temperatureindependent reactivity that has decreased over the last decade. At the same time, we know of no deliberate attempt to control the molecules dominating the reactivity at high temperatures -small aldehydes, alcohols, and the unknown VOCR.…”