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Title: Hygroscopicity of organic compounds as a function of carbon chain length, carboxyl, hydroperoxy, and carbonyl functional groups

The albedo and microphysical properties of clouds are controlled in part by the hygroscopicity of particles serving as cloud condensation nuclei (CCN). Hygroscopicity of complex organic mixtures in the atmosphere varies widely and remains challenging to predict. Here we present new measurements characterizing the CCN activity of pure compounds in which carbon chain length and the number of hydroperoxy, carboxyl, and carbonyl functional groups were systematically varied to establish the contributions of these groups to organic aerosol apparent hygroscopicity. Apparent hygroscopicity decreased with carbon chain length and increased with polar functional groups in the order carboxyl > hydroperoxy > carbonyl. Activation diameters at different supersaturations deviated from the -3/2 slope in log-log space predicted by Köhler theory, suggesting that water solubility limits CCN activity of particles composed of weakly functionalized organic compounds. Results are compared to a functional group contribution model that predicts CCN activity of organic compounds. The model performed well for most compounds but under-predicted the CCN activity of hydroperoxy groups. New best-fit hydroperoxy group/water interaction parameters were derived from the available CCN data. Lastly, these results may help improve estimates of the CCN activity of ambient organic aerosols from composition data.
 [1] ;  [2] ;  [2] ;  [3] ;  [4] ;  [2] ;  [3]
  1. Colorado State Univ., Fort Collins, CO (United States); Univ. of North Carolina, Chapel Hill, NC (United States)
  2. Univ. of Colorado, Boulder, CO (United States)
  3. Colorado State Univ., Fort Collins, CO (United States)
  4. North Carolina State Univ., Raleigh, NC (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 121; Journal Issue: 27; Journal ID: ISSN 1089-5639
American Chemical Society
Research Org:
Univ. of Colorado, Boulder, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
58 GEOSCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; organic aerosol; cloud condensation nuclei (CCN); aerosol hygroscopicity; Köhler theory; hydroperoxides; solubility; carboxylic acids; multifunctional carbonyls; group contribution method; UNIFAC
OSTI Identifier: