Water-soluble SOA from Alkene ozonolysis: composition and droplet activation kinetics inferences from analysis of CCN activity

Creators: Asa-Awuku, A.; Nenes, A.; Gao, S.; Flagan, R. C.; Seinfeld, J. H.

Abstract

Cloud formation characteristics of the water-soluble organic fraction (WSOC) of secondary organic aerosol (SOA) formed from the ozonolysis of alkene hydrocarbons (terpinolene, 1-methlycycloheptene and cycloheptene) are studied. Based on size-resolved measurements of CCN activity (of the pure and salted WSOC samples) we estimate the average molar volume and surface tension depression associated with the WSOC using Köhler Theory Analysis (KTA). Consistent with known speciation, the results suggest that the WSOC are composed of low molecular weight species, with an effective molar mass below 200 g mol^(−1). The water-soluble carbon is also surface-active, depressing surface tension 10–15% from that of pure water (at CCN-relevant concentrations). The inherent hygroscopicity parameter, κ, of the WSOC ranges between 0.17 and 0.25; if surface tension depression and molar volume effects are considered in κ, a remarkably constant "apparent" hygroscopicity ~0.3 emerges for all samples considered. This implies that the volume fraction of soluble material in the parent aerosol is the key composition parameter required for prediction of the SOA hygroscopicity, as shifts in molar volume across samples are compensated by changes in surface tension. Finally, using "threshold droplet growth analysis", the water-soluble organics in all samples considered do not affect CCN activation kinetics.

Additional Information

© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 7 June 2007 – Published in Atmos. Chem. Phys. Discuss.: 26 June 2007. Revised: 11 January 2010 – Accepted: 27 January 2010 – Published: 15 February 2010. Published by Copernicus Publications on behalf of the European Geosciences Union. The work in this study was supported by a NSF CAREER Award and a NASA Earth and Space Science Fellowship. Additional funding for the ozonolysis experiments and speciation was provided by the US Department of Energy Biological and Environmental Research Program DE-FG02-05ER63983, Electric Power Research Institute, and US Environmental Protection Agency RD-83107501-0. We would like to thank Rodney Weber and Chris Hennigan of the Georgia Institute of Technology for the use of their Total Organic Carbon (TOC) Turbo Siever analyzer and Dionex DX-500 ion chromatograph. Edited by: N. Pirrone.

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