Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 1 2009 10.5194/acpd-9-2645-2009 http://www.atmos-chem-phys-discuss.net/9/2645/2009/ http://www.atmos-chem-phys-discuss.net/9/2645/2009/acpd-9-2645-2009.html http://www.atmos-chem-phys-discuss.net/9/2645/2009/acpd-9-2645-2009.pdf 2645 2697 2009-01-28 Chemically-resolved aerosol volatility measurements from two megacity field studies J. A. Huffman K. S. Docherty A. C. Aiken M. J. Cubison I. M. Ulbrich P. F. DeCarlo D. Sueper J. T. Jayne D. R. Worsnop P. J. Ziemann J. L. Jimenez jose.jimenez@colorado.edu Cooperative Institute for Research in Environmental Sciences (CIRES), Boulder, Colorado, USA Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA Aerodyne Research, Inc., Billerica, MA, USA Air Pollution Research Center, University of California, Riverside, USA now at: Paul Scherrer Institute (PSI), Villigen, Switzerland The volatilities of different chemical species in ambient aerosols are important but remain poorly characterized. The coupling of a recently developed rapid temperature-stepping thermodenuder (TD, operated in the range 54–230°C) with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) during field studies in two polluted megacities has enabled the first direct characterization of chemically-resolved urban particle volatility. Measurements in Riverside, CA and Mexico City are generally consistent and show ambient nitrate as having the highest volatility of any AMS aerosol species while sulfate showed the lowest volatility. Total organic aerosol (OA) showed volatility intermediate between nitrate and sulfate, with an evaporation rate of 0.6% K^−1 near ambient temperature, although OA dominates the residual species at the highest temperatures. Different types of OA were characterized with marker ions, diurnal cycles, and positive matrix factorization (PMF) and show significant differences in volatility. Reduced hydrocarbon-like OA (HOA, a surrogate for primary OA, POA), oxygenated OA (OOA, a surrogate for secondary OA, SOA), and biomass-burning OA (BBOA) separated with PMF were all determined to be semi-volatile. The most aged OOA-1 and its dominant ion, CO₂⁺, consistently exhibited the lowest volatility, with HOA, BBOA, and associated ions for each among the highest. 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