title: Lubricating oil dominates primary organic aerosol emissions from motor vehicles.
abstract: Motor vehicles are major sources of primary organic aerosol (POA), which is a mixture of a large number of organic compounds that have not been comprehensively characterized. In this work, we apply a recently developed gas chromatography mass spectrometry approach utilizing "soft" vacuum ultraviolet photoionization to achieve unprecedented chemical characterization of motor vehicle POA emissions in a roadway tunnel with a mass closure of >60%. The observed POA was characterized by number of carbon atoms (NC), number of double bond equivalents (NDBE) and degree of molecular branching. Vehicular POA was observed to predominantly contain cycloalkanes with one or more rings and one or more branched alkyl side chains (≥80%) with low abundances of n-alkanes and aromatics (<5%), similar to "fresh" lubricating oil. The gas chromatography retention time data indicates that the cycloalkane ring structures are most likely dominated by cyclohexane and cyclopentane rings and not larger cycloalkanes. High molecular weight combustion byproducts, that is, alkenes, oxygenates, and aromatics, were not present in significant amounts. The observed carbon number and chemical composition of motor vehicle POA was consistent with lubricating oil being the dominant source from both gasoline and diesel-powered vehicles, with an additional smaller contribution from unburned diesel fuel and a negligible contribution from unburned gasoline.
authors.affiliation: Department of Environmental Science, Policy and Management, University of California , Berkeley, California 94720, United States.
authors.forename: David R
authors.initials: DR
authors.lastname: Worton
authors.forename: Gabriel
authors.initials: G
authors.lastname: Isaacman
authors.forename: Drew R
authors.initials: DR
authors.lastname: Gentner
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Dallmann
authors.forename: Arthur W H
authors.initials: AW
authors.lastname: Chan
authors.forename: Christopher
authors.initials: C
authors.lastname: Ruehl
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Kirchstetter
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Wilson
authors.forename: Robert A
authors.initials: RA
authors.lastname: Harley
authors.forename: Allen H
authors.initials: AH
authors.lastname: Goldstein
mesh_terms: D000336:Aerosols / Q000032:analysis*; D000393:Air Pollutants / Q000032:analysis*; D000473:Alkanes / Q000032:analysis; D001272:Atmosphere / Q000737:chemistry; D002244:Carbon / Q000032:analysis; D008401:Gas Chromatography-Mass Spectrometry; D005742:Gasoline / Q000032:analysis; D054327:Lubricants / Q000032:analysis*; D018986:Motor Vehicles; D009821:Oils / Q000032:analysis*; D009930:Organic Chemicals / Q000032:analysis*; D012495:San Francisco; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D000473:Alkanes; D005742:Gasoline; D054327:Lubricants; D009821:Oils; D009930:Organic Chemicals; D001335:Vehicle Emissions; D002244:Carbon