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

摘要

We examine the relationship between the number concentration ofboundary-layer cloud condensation nuclei (CCN) and light extinction toinvestigate underlying aerosol processes and satellite-based CCN estimates.For a variety of airborne and ground-based observations not dominated bydust, regression identifies the CCN (cm−3) at 0.4 ± 0.1%supersaturation with 100.3α +1.3σ0.75 where σ(Mm−1) is the 500 nm extinction coefficient by dried particles andα is the Angstrom exponent. The deviation of 1 kmhorizontal average data from this approximation is typically within a factorof 2.0. ∂logCCN / ∂logσ is less than unitybecause, among other explanations, growth processes generally make aerosolsscatter more light without increasing their number. This, barring specialmeteorology–aerosol connections, associates a doubling of aerosol opticaldepth with less than a doubling of CCN, contrary to previous studies basedon heavily averaged measurements or a satellite algorithm.