Publication Date:
2015-12-06
Description:
Secondary organic aerosol components (SOA) contribute significantly to the activation of cloud condensation nuclei (CCN) in the atmosphere. The CCN activity of internally-mixed submicron SOA particles is often parameterized assuming a size-independent single hygroscopicity parameter κ. In the experiments done in a large atmospheric reactor (SAPHIR, Jülich), we consistently observed size-dependent κ and particle composition for SOA from different precursors in the size range of 50 nm-200 nm. Smaller particles had higher κ and a higher degree of oxidation, although all particles were formed from the same reaction mixture. Since decreasing volatility and increasing hygroscopicity often co-vary with the degree of oxidation, the size dependence of composition and hence of CCN activity can be understood by enrichment of higher oxygenated, low volatility hygroscopic compounds in smaller particles. Neglecting the size dependence of κ can lead to significant bias in the prediction of the activated fraction of particles during cloud formation.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
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