ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-2825-2010 Characterization of a large biogenic secondary organic aerosol event from eastern Canadian forests Slowik J. G. 1 Stroud C. 2 Bottenheim J. W. 2 Brickell P. C. 2 Chang R. Y.-W. 1 Liggio J. 2 Makar P. A. 2 Martin R. V. 3 4 Moran M. D. 2 Shantz N. C. 1 2 Sjostedt S. J. 1 van Donkelaar A. 3 Vlasenko A. 1 2 Wiebe H. A. 2 Xia A. G. 2 Zhang J. 2 Leaitch W. R. 2 Abbatt J. P. D. 1 University of Toronto, Department of Chemistry, Toronto, ON, Canada Environment Canada, Science and Technology Branch, Toronto, ON, Canada Dalhousie University, Department of Physics and Atmospheric Science, Halifax, NS, Canada Harvard-Smithsonian Center for Astrophysics, Atomic and Molecular Physics Division, Cambridge, MA, USA 26 03 2010 10 6 2825 2845 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/2825/2010/acp-10-2825-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/2825/2010/acp-10-2825-2010.pdf

Measurements of aerosol composition, volatile organic compounds, and CO are used to determine biogenic secondary organic aerosol (SOA) concentrations at a rural site 70 km north of Toronto. These biogenic SOA levels are many times higher than past observations and occur during a period of increasing temperatures and outflow from Northern Ontario and Quebec forests in early summer. A regional chemical transport model approximately predicts the event timing and accurately predicts the aerosol loading, identifying the precursors as monoterpene emissions from the coniferous forest. The agreement between the measured and modeled biogenic aerosol concentrations contrasts with model underpredictions for polluted regions. Correlations of the oxygenated organic aerosol mass with tracers such as CO support a secondary aerosol source and distinguish biogenic, pollution, and biomass burning periods during the field campaign. Using the Master Chemical Mechanism, it is shown that the levels of CO observed during the biogenic event are consistent with a photochemical source arising from monoterpene oxidation. The biogenic aerosol mass correlates with satellite measurements of regional aerosol optical depth, indicating that the event extends across the eastern Canadian forest. This regional event correlates with increased temperatures, indicating that temperature-dependent forest emissions can significantly affect climate through enhanced direct optical scattering and higher cloud condensation nuclei numbers.

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