Chemistry and Physics Faculty Articles

Document Type

Article

Publication Date

2-15-2010

Publication Title

Atmospheric Chemistry and Physics

ISSN

1680-7316

Volume

10

Issue/No.

4

First Page

1585

Last Page

1597

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.

Comments

© Author(s) 2010. This work is distributed under the Creative Commons Attribution 3.0 License.

DOI

10.5194/acp-10-1585-2010

Peer Reviewed

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