Comment on “size distribution of sea-salt emissions as a function of relative humidity”

Abstract

Zhang et al. (2005) present a parameterization for what they term the growthfactor of a sea salt aerosol particle relative to its formation diameter, which they assertis a function of relative humidity alone and independent of an arbitrary referencerelative humidity. Here we note that this growth factor implicitly assumes an arbitraryreference relative humidity through the salinity of the seawater from which the particle isproduced and thus that the diameter at formation does not uniquely represent the amountof solute mass contained in a sea salt aerosol particle, in contrast to the equivalent dryradius (or diameter) or to the radius (or diameter) of the particle in equilibrium at a givenrelative humidity, typically used for this purpose. We present an alternativeparameterization for the RH growth factor of sea salt aerosol particles that is physicallybased, of more general applicability, more accurate, and valid at higher relative humidity.The dependence of the size of sea salt aerosol particles on relative humidity isimportant to numerous processes of interest: light scattering, gas-liquid exchange ofwater and trace gases, dry deposition, particle sampling, and the like, the accuratedescription of which requires accurate knowledge and representation of this dependence.Zhang et al. present a parameterization of the growth factor, which they define as theratio of the diameter of a sea salt aerosol particle at formation from seawater havingsalinity 35, D