Atmos. Chem. Phys. Discuss., 10, 27321-27359, 2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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Diurnally resolved particulate and VOC measurements at a rural site: indication of significant biogenic secondary organic aerosol formation
S. J. Sjostedt1,2, J. G. Slowik1, J. R. Brook2, R.Y.-W. Chang1, C. Mihele2, C. A. Stroud2, A. Vlasenko1,2, and J. P. D. Abbatt1
1Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada
2Environment Canada, Science and Technology Branch, Toronto, ON, M3H 5T4, Canada

Abstract. We report simultaneous measurements of volatile organic compound (VOC) mixing ratios including C6 to C8 aromatics, isoprene, monoterpenes, acetone and organic aerosol mass loadings at a rural location in Southwestern Ontario, Canada by Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and Aerosol Mass Spectrometry (AMS), respectively. During the three-week-long Border Air Quality and Meteorology Study in June–July 2007, air was sampled from a range of sources, including aged air from the polluted US Midwest, direct outflow from Detroit 50 km away, and clean air with higher biogenic input. After normalization to the diurnal profile of CO, a long-lived tracer, diurnal analyses show clear photochemical loss of reactive aromatics and production of oxygenated VOCs and secondary organic aerosol (SOA) during the daytime. Biogenic VOC mixing ratios increase during the daytime in accord with their light- and temperature-dependent sources. Long-lived species, such as hydrocarbon-like organic aerosol and benzene show little to no photochemical reactivity on this timescale. From the normalized diurnal profiles of VOCs, an estimate of OH concentrations during the daytime, measured O3 concentrations, and laboratory SOA yields, we calculate integrated organic aerosol production amounts associated with each measured SOA precursor. Depending on whether the SOA formation is occurring in a low- or high-NOx regime, we estimate that the biogenic gases contribute between 10 to 36 times as much SOA as do the aromatic precursors, making this a highly biogenically dominated region for SOA formation. The conclusion that biogenic SOA formation is of significance to air quality in this region is supported by detailed air quality modeling during this period (Stroud et al., 2010).

Citation: Sjostedt, S. J., Slowik, J. G., Brook, J. R., Chang, R.Y.-W., Mihele, C., Stroud, C. A., Vlasenko, A., and Abbatt, J. P. D.: Diurnally resolved particulate and VOC measurements at a rural site: indication of significant biogenic secondary organic aerosol formation, Atmos. Chem. Phys. Discuss., 10, 27321-27359, doi:10.5194/acpd-10-27321-2010, 2010.
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