Laboratory simulations and parameterization of the primary marine aerosol production

Abstract

A major source of the primary marine aerosol is the bursting of air bubbles produced by breaking waves. Several source parameterizations are available from the literature, usually limited to particles with a dry diameter Dp > 1 μm. The objective of this work is to extend the current knowledge to submicrometer particles. Bubbles were generated in synthetic seawater using a sintered glass filter, with a size spectra that are only partly the same spectra as measured in the field. Bubble spectra, and size distributions of the resulting aerosol (0.020-20.0 μm Dp) of the resulting aerosol, were measured for different salinity, water temperature (Tw), and bubble flux. The spectra show a minimum at ∼1 μm Dp, which separates two modes, one at ∼0.1 μm, with the largest number of particles, and one at 2.5 μm Dp. The modes show different behavior with the variation of salinity and water temperature. When the water temperature increases, the number concentration Np decreases for Dp < 0.07 μm, whereas for Dp > 0.35 μm, Np increases. The salinity effect suggests different droplet formation processes for droplets smaller and larger than 0.2 μm Dp. The number of particles produced per size increment, time unit, and whitecap surface (φ) is described as a linear function of Tw and a polynomial function of Dp. Combining φ with the whitecap coverage fraction W (in percent), an expression results for the primary marine aerosol source flux dFo/dlogDp = W φ (m-2 s-1 ). The results are compared with other commonly used formulations as well as with recent field observations. Implications for aerosol-induced effects on climate are discussed.