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The relationship between cloud condensation nuclei (CCN) concentration and...

Shinozuka, Y., A. Clarke, A. Nenes, A. Jefferson, R. Wood, C. S. McNaughton, J. Ström, P. Tunved, J. Redemann, L. Thornhill, R. Moore, T. L. Lathem, J. J. Lin, and Y. J. Yoon (2015), The relationship between cloud condensation nuclei (CCN) concentration and light extinction of dried particles: indications of underlying aerosol processes and implications for satellite-based CCN estimates, Atmos. Chem. Phys., 15, 7585-7604, doi:10.5194/acp-15-7585-2015.

We examine the relationship between the number concentration of boundary-layer cloud condensation nuclei (CCN) and light extinction to investigate underlying aerosol processes and satellite-based CCN estimates. For a variety of airborne and ground-based observations not dominated by dust, regression identifies the CCN (cm−3 ) at 0.4 ± 0.1 % supersaturation with 100.3α+1.3 σ 0.75 where σ (Mm−1 ) is the 500 nm extinction coefficient by dried particles and α is the Angstrom exponent. The deviation of 1 km horizontal average data from this approximation is typically within a factor of 2.0. ∂logCCN / ∂logσ is less than unity because, among other explanations, growth processes generally make aerosols scatter more light without increasing their number. This, barring special meteorology–aerosol connections, associates a doubling of aerosol optical depth with less than a doubling of CCN, contrary to previous studies based on heavily averaged measurements or a satellite algorithm.

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