Abstract
Abstract. A series of smog chamber experiments were conducted to investigate the transformation of primary organic aerosol (POA) and formation of secondary organic aerosol (SOA) during the photooxidation of dilute exhaust from a fleet of gasoline and diesel motor vehicles and two gas-turbine engines. In experiments where POA was present in the chamber at the onset of photooxidation, positive matrix factorization (PMF) was used to determine separate POA and SOA factors from aerosol mass spectrometer data. A 2-factor solution, with one POA factor and one SOA factor, was sufficient to describe the organic aerosol for gasoline vehicles, diesel vehicles, and one of the gas-turbine engines. Experiments with the second gas-turbine engine required a 3-factor PMF solution with a POA factor and two SOA factors. Results from the PMF analysis were compared to the residual method for determining SOA and POA mass concentrations. The residual method apportioned a larger fraction of the organic aerosol mass as POA because it assumes that all mass at m / z 57 is associated with POA. The POA mass spectrum for the gasoline and diesel vehicles exhibited high abundances of the CnH2n+1 series of ions (m / z 43, 57, etc.) and was similar to the mass spectra of the hydrocarbon-like organic aerosol factor determined from ambient data sets with one exception, a diesel vehicle equipped with a diesel oxidation catalyst. POA mass spectra for the gas-turbine engines are enriched in the CnH2n−1 series of ions (m / z 41, 55, etc.), consistent with the composition of the lubricating oil used in these engines. The SOA formed from the three sources exhibits high abundances of m / z 44 and 43, indicative of mild oxidation. The SOA mass spectra are consistent with less-oxidized ambient SV-OOA (semivolatile oxygenated organic aerosols) and fall within the triangular region of f44 versus f43 defined by ambient measurements. However there is poor absolute agreement between the experimentally derived SOA mass spectra and ambient OOA factors, though this poor agreement should be expected based on the variability of ambient OOA factors. Van Krevelen analysis of the POA and SOA factors for gasoline and diesel experiments reveal slopes of −0.50 and −0.40, respectively. This suggests that the oxidation chemistry in these experiments is a combination of carboxylic acid and alcohol/peroxide formation, consistent with ambient oxidation chemistry.
Highlights
Organic aerosols (OA) comprise roughly 50 % of ambient fine particulate matter (PM) mass (Kanakidou et al, 2005)
Atmospheric OA is commonly classified as either primary organic aerosol (POA), which is directly emitted from combustion and other sources, or secondary organic aerosol (SOA), which results from oxidative atmospheric chemistry (Donahue et al, 2009)
We present aerosol mass spectrometers (AMS) analysis of OA from smog chamber experiments using dilute exhaust from gasoline vehicles, diesel vehicles, and gas-turbine engines
Summary
Organic aerosols (OA) comprise roughly 50 % of ambient fine particulate matter (PM) mass (Kanakidou et al, 2005). Numerous smog chamber experiments have investigated the photochemical formation of SOA from dilute combustion exhaust from many sources, including diesel engines and vehicles (Chirico et al, 2010; Robinson et al, 2007; Sage et al., 2008; Samy and Zielinska, 2010), automobiles (Nordin et al, 2012; Platt et al, 2012), gas-turbine engines (Miracolo et al, 2011, 2012), and biomass burning (Grieshop et al, 2009a, b; Hennigan et al, 2011; Heringa et al, 2011). Much like the custom principle component analysis of Zhang et al (2005), the residual spectrum analysis assumed that all of the signal at m/z 57 (for a unit mass resolution AMS) was associated with POA, and all of the m/z 44 signal was associated with SOA Using this method, Sage et al demonstrated that SOA formed from the photooxidation of dilute diesel engine exhaust had a similar mass spectrum to ambient oxidized organic aerosol. We compare the performance of the residual method and PMF at determining the POA–SOA split in these experiments
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