title: Secondary organic aerosol formation from in-use motor vehicle emissions using a potential aerosol mass reactor.
abstract: Secondary organic aerosol (SOA) formation from in-use vehicle emissions was investigated using a potential aerosol mass (PAM) flow reactor deployed in a highway tunnel in Pittsburgh, Pennsylvania. Experiments consisted of passing exhaust-dominated tunnel air through a PAM reactor over integrated hydroxyl radical (OH) exposures ranging from ∼ 0.3 to 9.3 days of equivalent atmospheric oxidation. Experiments were performed during heavy traffic periods when the fleet was at least 80% light-duty gasoline vehicles on a fuel-consumption basis. The peak SOA production occurred after 2-3 days of equivalent atmospheric oxidation. Additional OH exposure decreased the SOA production presumably due to a shift from functionalization to fragmentation dominated reaction mechanisms. Photo-oxidation also produced substantial ammonium nitrate, often exceeding the mass of SOA. Analysis with an SOA model highlight that unspeciated organics (i.e., unresolved complex mixture) are a very important class of precursors and that multigenerational processing of both gases and particles is important at longer time scales. The chemical evolution of the organic aerosol inside the PAM reactor appears to be similar to that observed in the atmosphere. The mass spectrum of the unoxidized primary organic aerosol closely resembles ambient hydrocarbon-like organic aerosol (HOA). After aging the exhaust equivalent to a few hours of atmospheric oxidation, the organic aerosol most closely resembles semivolatile oxygenated organic aerosol (SV-OOA) and then low-volatility organic aerosol (LV-OOA) at higher OH exposures. Scaling the data suggests that mobile sources contribute ∼ 2.9 ± 1.6 Tg SOA yr(-1) in the United States, which is a factor of 6 greater than all mobile source particulate matter emissions reported by the National Emissions Inventory. This highlights the important contribution of SOA formation from vehicle exhaust to ambient particulate matter concentrations in urban areas.
authors.affiliation: Department of Civil and Environmental Engineering, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Tkacik
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Lambe
authors.forename: Shantanu
authors.initials: S
authors.lastname: Jathar
authors.forename: Xiang
authors.initials: X
authors.lastname: Li
authors.forename: Albert A
authors.initials: AA
authors.lastname: Presto
authors.forename: Yunliang
authors.initials: Y
authors.lastname: Zhao
authors.forename: Donald
authors.initials: D
authors.lastname: Blake
authors.forename: Simone
authors.initials: S
authors.lastname: Meinardi
authors.forename: John T
authors.initials: JT
authors.lastname: Jayne
authors.forename: Philip L
authors.initials: PL
authors.lastname: Croteau
authors.forename: Allen L
authors.initials: AL
authors.lastname: Robinson
mesh_terms: D000336:Aerosols / Q000032:analysis* / Q000737:chemistry*; D000393:Air Pollutants / Q000032:analysis*; D001272:Atmosphere / Q000032:analysis; D002947:Cities; D005742:Gasoline / Q000032:analysis; D017665:Hydroxyl Radical / Q000032:analysis; D009566:Nitrates / Q000032:analysis; D009930:Organic Chemicals / Q000032:analysis; D010084:Oxidation-Reduction; D052638:Particulate Matter / Q000032:analysis; D010414:Pennsylvania; D014481:United States; D001335:Vehicle Emissions / Q000032:analysis*; D055549:Volatile Organic Compounds / Q000737:chemistry
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D005742:Gasoline; D009566:Nitrates; D009930:Organic Chemicals; D052638:Particulate Matter; D001335:Vehicle Emissions; D055549:Volatile Organic Compounds; D017665:Hydroxyl Radical; C006568:ammonium nitrate