title: Daily variation in chemical characteristics of urban ultrafine aerosols and inference of their sources.
abstract: A summer air quality monitoring campaign focusing on daily variation of ultrafine (<180 nm in diameter) particle chemical characteristics was conducted in a typical urban site in Los Angeles during June-July 2006. Ultrafine particles (UFP) were collected weekly for two 3 h periods each day, one to capture the morning commute (06:00-09:00 PDT) (Pacific Daylight Time) and one to investigate photochemically altered particles (13:00-16:00 PDT). Samples were analyzed for ionic compounds, metals, trace elements, elemental carbon, and organic carbon. In addition, measurements of individual organic species and their variation with time of day at the urban site were conducted. The relative abundances of alkanes, PAH, and hopanes in the morning denote a strong influence of commute traffic emissions on ultrafine particle concentrations. By contrast, afternoon concentrations of oxygenated organic acids and sulfate rose, while other species were diluted by increased mixing height or lost due to increasing temperature. These are clear indicators that secondary photochemical reactions are a major formation mechanism of ultrafine aerosols in the afternoon. The concentrations of organic species originating from vehicular emissions measured in this study compare favorably to those from freeway-adjacent measurements by using CO2 concentrations to adjust for dilution, demonstrating the effectiveness of this tool for relating sites affected by vehicular emissions.
authors.affiliation: Department of Civil and Environmental Engineering, University of Southern California, 3620 South Vermont Avenue, Los Angeles, California 90089, USA.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Ning
authors.forename: Michael D
authors.initials: MD
authors.lastname: Geller
authors.forename: Katharine F
authors.initials: KF
authors.lastname: Moore
authors.forename: Rebecca
authors.initials: R
authors.lastname: Sheesley
authors.forename: James J
authors.initials: JJ
authors.lastname: Schauer
authors.forename: Constantinos
authors.initials: C
authors.lastname: Sioutas
mesh_terms: D000143:Acids / Q000032:analysis; D000336:Aerosols / Q000032:analysis*; D000392:Air Movements; D000393:Air Pollutants / Q000032:analysis*; D002244:Carbon / Q000032:analysis; D002245:Carbon Dioxide / Q000032:analysis; D002947:Cities; D004784:Environmental Monitoring; D006801:Humans; D008670:Metals / Q000032:analysis; D009930:Organic Chemicals / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis*; D012621:Seasons; D012828:Silicones; D013431:Sulfates / Q000032:analysis; D013997:Time Factors; D014131:Trace Elements / Q000032:analysis; D001335:Vehicle Emissions
chemical_list: D000143:Acids; D000336:Aerosols; D000393:Air Pollutants; D008670:Metals; D009930:Organic Chemicals; D052638:Particulate Matter; D012828:Silicones; D013431:Sulfates; D014131:Trace Elements; D001335:Vehicle Emissions; D002245:Carbon Dioxide; D002244:Carbon