Showing papers by "John T. Jayne published in 2014"

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.

Submicron aerosol source apportionment of wintertime pollution in Paris, France by double positive matrix factorization (PMF 2 ) using an aerosol chemical speciation monitor (ACSM) and a multi-wavelength Aethalometer

Abstract: . Online non-refractory submicron aerosol mass spectrometer (AMS) measurements in urban areas have successfully allowed the apportionment of specific sources and/or physical and chemical properties of the organic fraction. However, in order to be fully representative of PM pollution, a comprehensive source apportionment analysis is needed by taking into account all major components of submicron aerosols, creating strengthened bonds between the organic components and pollution sources. We present here a novel two-step methodology to perform such an analysis, by taking advantage of high time resolution of monitoring instruments: the aerosol chemical speciation monitor (ACSM) and the multi-wavelength absorption measurements (Aethalometer AE31) in Paris, France. As a first step, organic aerosols (OA) were deconvolved to hydrocarbon-like OA (HOA), biomass burning OA (BBOA) and oxygenated OA (OOA) with positive matrix factorization (PMF), and black carbon was deconvolved into its wood burning and fossil fuel combustion fractions. A second PMF analysis was then carried out with organic factors, BC fractions and inorganic species (nitrate, sulfate, ammonium, chloride), leading to a four-factor solution allowing highly time-resolved characterization of the major sources of PM1. Outputs of this PMF2 include two dominant combustion sources (wood burning and traffic) as well as semi-volatile and low-volatile secondary aerosols. While HOA is found to be emitted by both wood burning and traffic, the latter sources occurred to significantly contribute also to OOA.

The First Combined Thermal Desorption Aerosol Gas Chromatograph—Aerosol Mass Spectrometer (TAG-AMS)

Abstract: To address the critical need for improving the chemical characterization of the organic composition of ambient particulate matter, we introduce a combined thermal desorption aerosol gas chromatograph—aerosol mass spectrometer (TAG-AMS). The TAG system provides in-situ speciation of organic chemicals in ambient aerosol particles with hourly time resolution for marker compounds indicative of sources and transformation processes. However, by itself the TAG cannot separate by particle size and it typically speciates and quantifies only a fraction of the organic aerosol (OA) mass. The AMS is a real-time, in-situ instrument that provides quantitative size distributions and mass loadings for ambient fine OA and major inorganic fractions; however, by itself the AMS has limited ability for identification of individual organic compounds due to the electron impact ionization detection scheme used without prior molecular separation. The combined TAG-AMS system provides real-time detection by AMS followed by semiconti...