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Size‐dependent hygroscopicity parameter ( κ ) and chemical composition of secondary organic cloud condensation nuclei
Author(s) -
Zhao D. F.,
Buchholz A.,
Kortner B.,
Schlag P.,
Rubach F.,
KiendlerScharr A.,
Tillmann R.,
Wahner A.,
Flores J. M.,
Rudich Y.,
Watne Å. K.,
Hallquist M.,
Wildt J.,
Mentel Th. F.
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl066497
Subject(s) - cloud condensation nuclei , volatility (finance) , aerosol , particle size , condensation , chemical composition , materials science , particle (ecology) , particle size distribution , fraction (chemistry) , chemistry , thermodynamics , physics , organic chemistry , oceanography , financial economics , economics , geology
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, Simulation of Atmospheric PHotochemistry In a large Reaction chamber, 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 covary 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.