title: Methods of characterizing the distribution of exhaust emissions from light-duty, gasoline-powered motor vehicles in the U.S. fleet.
abstract: Mobile sources significantly contribute to ambient concentrations of airborne particulate matter (PM). Source apportionment studies for PM10 (PM < or = 10 microm in aerodynamic diameter) and PM2.5 (PM < or = 2.5 microm in aerodynamic diameter) indicate that mobile sources can be responsible for over half of the ambient PM measured in an urban area. Recent source apportionment studies attempted to differentiate between contributions from gasoline and diesel motor vehicle combustion. Several source apportionment studies conducted in the United States suggested that gasoline combustion from mobile sources contributed more to ambient PM than diesel combustion. However, existing emission inventories for the United States indicated that diesels contribute more than gasoline vehicles to ambient PM concentrations. A comprehensive testing program was initiated in the Kansas City metropolitan area to measure PM emissions in the light-duty, gasoline-powered, on-road mobile source fleet to provide data for PM inventory and emissions modeling. The vehicle recruitment design produced a sample that could represent the regional fleet, and by extension, the national fleet. All vehicles were recruited from a stratified sample on the basis of vehicle class (car, truck) and model-year group. The pool of available vehicles was drawn primarily from a sample of vehicle owners designed to represent the selected demographic and geographic characteristics of the Kansas City population. Emissions testing utilized a portable, light-duty chassis dynamometer with vehicles tested using the LA-92 driving cycle, on-board emissions measurement systems, and remote sensing devices. Particulate mass emissions were the focus of the study, with continuous and integrated samples collected. In addition, sample analyses included criteria gases (carbon monoxide, carbon dioxide, nitric oxide/nitrogen dioxide, hydrocarbons), air toxics (speciated volatile organic compounds), and PM constituents (elemental/organic carbon, metals, semi-volatile organic compounds). Results indicated that PM emissions from the in-use fleet varied by up to 3 orders of magnitude, with emissions generally increasing for older model-year vehicles. The study also identified a strong influence of ambient temperature on vehicle PM mass emissions, with rates increasing with decreasing temperatures.
authors.affiliation: National Vehicle and Fuel Emissions Laboratory, Office of Transportation and Air Quality, U.S. Environmental Protection Agency, Ann Arbor, MI, USA.
authors.forename: Carl R
authors.initials: CR
authors.lastname: Fulper
authors.forename: Sandeep
authors.initials: S
authors.lastname: Kishan
authors.forename: Richard W
authors.initials: RW
authors.lastname: Baldauf
authors.forename: Michael
authors.initials: M
authors.lastname: Sabisch
authors.forename: Jim
authors.initials: J
authors.lastname: Warila
authors.forename: Eric M
authors.initials: EM
authors.lastname: Fujit
authors.forename: Carl
authors.initials: C
authors.lastname: Scarbro
authors.forename: William S
authors.initials: WS
authors.lastname: Crews
authors.forename: Richard
authors.initials: R
authors.lastname: Snow
authors.forename: Peter
authors.initials: P
authors.lastname: Gabele
authors.forename: Robert
authors.initials: R
authors.lastname: Santos
authors.forename: Eugene
authors.initials: E
authors.lastname: Tierney
authors.forename: Bruce
authors.initials: B
authors.lastname: Cantrell
mesh_terms: D000395:Air Pollutants, Occupational / Q000032:analysis*; D001336:Automobiles; D004602:Elements; D004784:Environmental Monitoring; D005742:Gasoline; D009930:Organic Chemicals / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis; D012621:Seasons; D013696:Temperature; D014481:United States; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000395:Air Pollutants, Occupational; D004602:Elements; D005742:Gasoline; D009930:Organic Chemicals; D052638:Particulate Matter; D001335:Vehicle Emissions