Marine condensation nucleus generation inferred from whitecap simulation tank results

Abstract

The condensation nuclei (CN) produced during a set of experiments in the Whitecap Simultation Tank at University College, Galway, were measured with a TSI 3020 nucleus counter. The total number of CN produced per breaking wave event was 3.5 ± 0.5 × 107 for a seawater temperature near 15°C. The CN production per unit area of whitecap (108 m−2) and the previously observed whitecap time decay constant of ∼3.5 s implies a whitecap CN flux Fw of ∼2.8 + 0.9 × 107 m−2 s−1. This can be combined with the whitecap coverage W versus 10 m wind speed U relation of E. C. Monahan and I. O'Muircheartaigh (1980), W(U) = 3.84 × 10−6 U3.41, to estimate the general oceanic CN flux F0 = WFW. For U = 10 m s−1, this relation gives W = 1%, and thus F0 is ∼2.8 × 105 m−2 s−1. Using the same Whitecap Simulation Tank and a PMS classical aerosol spectrometer, E. C. Monahan et al. (1982) determined that the whitecap flux Fw of giant particles (radii > 1 μm at relative humidity = 80%) was ∼2 × 106 m−2S−1. Clearly, most of the CN produced by this whitecap simulation are of submicron size, and this was also the case in the model breaking wave experiments of R. J. Cipriano et al. (1983). Both laboratory whitecap simulations suggest that the ocean contributes significantly to the CN and cloud condensation nuclei populations of the marine atmospheric boundary layer far from land.