Open AccessFoam droplets generated from natural and artificial seawaters
Author(s) -
Tyree Corey A.,
Hellion Virginie M.,
Alexandrova Olga A.,
Allen Jonathan O.
Publication year - 2007
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2006jd007729
Subject(s) - seawater , aerosol , flux (metallurgy) , artificial seawater , particle (ecology) , sea salt , range (aeronautics) , cloud condensation nuclei , materials science , particle size , sea spray , atmospheric sciences , meteorology , chemistry , physics , composite material , oceanography , geology , metallurgy
Submicrometer sea salt aerosol (SSA) particles are routinely observed in the remote marine boundary layer (MBL); these aerosols include cloud condensation nuclei and so affect the earth's radiative balance. Here foams designed to mimic oceanic whitecaps were generated in the laboratory using a range of bubbling flow rates and aqueous media: unfiltered seawater, filtered seawater, artificial seawater, and mixtures of filtered and artificial seawater. The number and sizes of dried foam droplets in the particle diameter, D p , range 15–673 nm were measured. Particle size distributions for natural and artificial seawaters were unimodal with a d N /d log D p mode at D p ≈ 100 nm (≈200 nm at 80% RH). The foam droplet mode falls within the range of reported mode diameters ( D p = 40–200 nm) for submicrometer SSA particles observed in the remote MBL. The present laboratory results were scaled up to estimate submicrometer SSA particle fluxes; this extrapolation supports the hypothesis that foam droplets are the most important source of SSA particles by number. The foam droplet flux from the oceans was estimated to be 980 cm −2 s −1 for a fractional white cap coverage, W , of 0.2%. These results compared well with foam droplet fluxes reported elsewhere. The origins of variability in foam droplet fluxes were also evaluated. Natural organic matter affected foam droplet flux by a factor of 1.5; this was less than (1) the effect of bubbling flow rate on foam droplet flux (factor of 5) and (2) the uncertainty in W (factor of 3–7).