Carnegie Mellon University
Browse
- No file added yet -

Relating CCN activity, volatility, and droplet growth kinetics of β-caryophyllene secondary organic aerosol

Download (1.52 MB)
journal contribution
posted on 2009-02-01, 00:00 authored by A. Asa-Awuku, G. J. Engelhart, B. H. Lee, Spyros N. Pandis, A. Nenes

This study investigates the droplet formation characteristics of secondary organic aerosol (SOA) formed during the ozonolysis of sesquiterpene β-caryophyllene (with and without hydroxyl radicals present). Emphasis is placed on understanding the role of semi-volatile material on Cloud Condensation Nucleus (CCN) activity and droplet growth kinetics. Aging of β-caryophyllene SOA significantly affects all CCN-relevant properties measured throughout the experiments. Using a thermodenuder and two CCN instruments, we find that CCN activity is a strong function of temperature (activation diameter at ~0.6% supersaturation: 100±10 nm at 20°C and 130±10 nm at 35°C), suggesting that the hygroscopic fraction of the SOA is volatile. The water-soluble organic carbon (WSOC) is extracted from the SOA and characterized with Köhler Theory Analysis (KTA); the results suggest that the WSOC is composed of low molecular weight (<200 g mol−1) slightly surface-active material that constitute 5–15% of the SOA mass. These properties are similar to the water-soluble fraction of monoterpene SOA, suggesting that predictive understanding of SOA CCN activity requires knowledge of the WSOC fraction but not its exact speciation. Droplet growth kinetics of the CCN are found to be strongly anticorrelated with WSOC fraction, suggesting that the insoluble material in the SOA forms a kinetic barrier that delays droplet growth. Overall, volatilization effects can increase activation diameters by 30%, and depress droplet growth rate by a factor of two; these results may have important implications for the droplet formation characteristics of SOA, and the atmospheric relevance of CCN measurements carried out at temperatures different from ambient.

History

Publisher Statement

© Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License

Date

2009-02-01

Usage metrics

    Licence

    Exports

    RefWorks
    BibTeX
    Ref. manager
    Endnote
    DataCite
    NLM
    DC