Atmos. Chem. Phys. Discuss., 8, 17095-17130, 2008
www.atmos-chem-phys-discuss.net/8/17095/2008/
doi:10.5194/acpd-8-17095-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Laboratory investigation of photochemical oxidation of organic aerosol from wood fires – Part 2: Analysis of aerosol mass spectrometer data
A. P. Grieshop, N. M. Donahue, and A. L. Robinson
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USA

Abstract. Experiments were conducted to investigate the effects of photo-oxidation on organic aerosol (OA) in dilute wood smoke by exposing emissions from soft- and hard-wood fires to UV light in a smog chamber. This paper focuses on changes in OA composition measured using a unit mass resolution quadrupole Aerosol Mass Spectrometer (AMS). The results highlight how photochemical processing can lead to considerable evolution of the mass, the volatility and the level of oxygenation of biomass-burning OA. Photochemical oxidation produced substantial new OA, more than doubling the primary contribution after a few hours of aging under typical summertime conditions. Aging decreased the OA volatility of the total OA as measured with a thermodenuder; it also made the OA progressively more oxygenated in every experiment. With explicit knowledge of the condensed-phase mass spectrum (MS) of the primary emissions from each fire, each MS can be decomposed into primary and residual spectra throughout the experiment. The residual spectra provide an estimate of the composition of the photochemically produced OA. These spectra are also very similar to those of the oxygenated OA that dominates ambient AMS datasets. In addition, aged wood smoke spectra are shown to be similar to those from OA created by photo-oxidized dilute diesel exhaust and aged biomass-burning OA measured in urban and remote locations. This demonstrates that the oxygenated OA observed in the atmosphere can be produced by photochemical aging of dilute emissions from combustion of fuels containing both modern and fossil carbon.

Citation: Grieshop, A. P., Donahue, N. M., and Robinson, A. L.: Laboratory investigation of photochemical oxidation of organic aerosol from wood fires – Part 2: Analysis of aerosol mass spectrometer data, Atmos. Chem. Phys. Discuss., 8, 17095-17130, doi:10.5194/acpd-8-17095-2008, 2008.
 
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