1Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen, Switzerland
2National Centre for Atmospheric Science (NCAS), School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester, UK
3Department of Chemistry and Biochemistry, and CIRES, University of Colorado, UCB 216, Boulder, CO 80309-0216, USA
4Aerodyne Research, Billerica, MA, USA
5Department of Physics, University of Helsinki, 000014, Helsinki, Finland
6Department of Atmospheric Sciences, Texas A&M University, 3150 TAMU, College Station, TX 77843-3150, USA
7Pacific Northwest National Laboratory, Richland, WA 99352, USA
*now at: PH department, CERN, 1211, Geneva, Switzerland
**now at: Institute for Atmospheric and Environmental Sciences, Goethe-University Frankfurt, Frankfurt am Main, Germany
***now at: Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Received: 19 Jul 2010 – Discussion started: 17 Aug 2010
Abstract. A hygroscopicity tandem differential mobility analyzer (HTDMA) was used to measure the water uptake (hygroscopicity) of secondary organic aerosol (SOA) formed during the chemical and photochemical oxidation of several organic precursors in a smog chamber. Electron ionization mass spectra of the non-refractory submicron aerosol were simultaneously determined with an aerosol mass spectrometer (AMS), and correlations between the two different signals were investigated. SOA hygroscopicity was found to strongly correlate with the relative abundance of the ion signal m/z 44 expressed as a fraction of total organic signal (f44). m/z 44 is due mostly to the ion fragment CO2+ for all types of SOA systems studied, and has been previously shown to strongly correlate with organic O/C for ambient and chamber OA. The analysis was also performed on ambient OA from two field experiments at the remote site Jungfraujoch, and the megacity Mexico City, where similar results were found. A simple empirical linear relation between the hygroscopicity of OA at subsaturated RH, as given by the hygroscopic growth factor (GF) or "ϰorg" parameter, and f44 was determined and is given by ϰorg = 2.2 × f44 − 0.13. This approximation can be further verified and refined as the database for AMS and HTDMA measurements is constantly being expanded around the world. The use of this approximation could introduce an important simplification in the parameterization of hygroscopicity of OA in atmospheric models, since f44 is correlated with the photochemical age of an air mass.
Revised: 25 Jan 2011 – Accepted: 30 Jan 2011 – Published: 10 Feb 2011
Duplissy, J., DeCarlo, P. F., Dommen, J., Alfarra, M. R., Metzger, A., Barmpadimos, I., Prevot, A. S. H., Weingartner, E., Tritscher, T., Gysel, M., Aiken, A. C., Jimenez, J. L., Canagaratna, M. R., Worsnop, D. R., Collins, D. R., Tomlinson, J., and Baltensperger, U.: Relating hygroscopicity and composition of organic aerosol particulate matter, Atmos. Chem. Phys., 11, 1155-1165, doi:10.5194/acp-11-1155-2011, 2011.