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On supersaturation spectrum and size distributions of cloud condensation nuclei
Author(s) -
Ji Qiang,
Shaw Glenn E.
Publication year - 1998
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 - 10.1029/98gl01404
Subject(s) - supersaturation , cloud condensation nuclei , power law , exponential function , exponential distribution , physics , condensation , gamma distribution , spectral line , aerosol , chemistry , thermodynamics , meteorology , mathematics , statistics , quantum mechanics , mathematical analysis
The supersaturation spectra of cloud condensation nuclei (CCN) are sometimes S‐shaped and always asymptotically approach a limiting value as supersaturation becomes more than several percent. Such a complex shape can correspond to a bell‐shaped size distribution of sub‐micron aerosols. We found that an exponential expression N = N 0 (1‐exp[− B S K ]) fits measured supersaturation spectra better than the commonly used power law expression N = C S K , where N is the number concentration of CCN at the supersaturation S , N 0 is the total number concentration of CCN, B , C and K are empirical coefficients. The exponential expression and the power law are related. For example, at S ∼ 0%, the exponential expression reduces to the power law, with C ∼ N 0 B . The derived size distribution from the exponential expression agrees closely with measured size distributions for laboratory salts, but not for aerosols in polluted airmasses. The disagreement in polluted airmasses suggests that CCN have complex physiochemistry.