Empirical Predictions of CCN from Aerosol Optical Properties

Anne Jefferson NOAA

Category: Aerosol-Cloud-Radiation Interactions

Working Group: Aerosol Life Cycle

Aerosol optical properties exhibit a close correlation with the CCN number concentration and can be used as a proxy for determining the CCN number concentration as a function of the percent super saturation. An empirical method was developed to fit the aerosol single-scatter albedo and the backscatter fraction at 450 nm from in situ AOS measurements to the Twomey k and C power law fit parameters in the equation CCN = C*(%SS)k. The empirical model was run on data from four ARM surface sites: SGP, FKB, HFE, and GRA. A linear fit of the empirical fit vs measured CCN at %SS from 0.2 to 0.85 gave slopes that range from 0.88 for Graciosa, Azores to 0.98 for the SGP site in Oklahoma. Correlation coefficients ranged from 0.59 for Graciosa and 0.77 for FKB in Germany. Error in the model is expected to result from measurement limitations of small particles by the nephelometer. Mie scattering calculations of the aerosol backscatter fraction at 450 nm indicate that the nephelometer has a lower size range of about 100–120 nm, while critical CCN activation diameters are predicted to be between 50–200 nm for ambient aerosol of mixed inorganic/organic concentration.

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