title: 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.
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720-1710, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Harley
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Hooper
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Kean
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Kirchstetter
authors.forename: James M
authors.initials: JM
authors.lastname: Hesson
authors.forename: Nancy T
authors.initials: NT
authors.lastname: Balberan
authors.forename: Eric D
authors.initials: ED
authors.lastname: Stevenson
authors.forename: Gary R
authors.initials: GR
authors.lastname: Kendall
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000517:prevention & control*; D001554:Benzene / Q000032:analysis*; D002248:Carbon Monoxide / Q000032:analysis*; D002274:Carcinogens, Environmental / Q000032:analysis*; D004777:Environment; D004784:Environmental Monitoring; D005742:Gasoline / Q000032:analysis*; D012495:San Francisco; D012621:Seasons; D014186:Transportation; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D002274:Carcinogens, Environmental; D005742:Gasoline; D001335:Vehicle Emissions; D002248:Carbon Monoxide; D001554:Benzene