MODELING SEA-SALT AEROSOLS IN THE ATMOSPHERE .1. MODEL DEVELOPMENT

A simulation of the processes of sea-salt aerosol generation, diffusiv e transport, transformation, and removal as a function of particle siz e is incorporated into a one-dimensional version of the Canadian gener al climate model (GCMII). This model was then run in the North Atlanti c between Iceland and Ireland during the period of January-March. Mode l predictions are compared to observations of sea-salt aerosols select ed from a review of available studies that were subjected to strict sc reening criteria to ensure their representativeness. The number and ma ss size distribution and the wind dependency of total sea-salt aerosol mass concentrations predicted by the model compare well with observat ions. The modeled dependence of sea-salt aerosol concentration in the surface layer (chi, mu g m(-3)) on 10-m wind speed (U-10, m s(-1)) is given by chi = be(aU10). Simulations show that both a and b change wit h location. The value a and b range from 0.20 and 3.1 for Mace Head, I reland to 0.26, and 1.4 for Heimaey, Iceland. The dependence of chi on surface wind speed is weaker for smaller particles and for particles at higher altitudes. The residence time of sea-salt aerosols in the fi rst atmospheric layer (0-166 m) ranges from 30 min for large particles (r = 4-8 mu m) to similar to 60 hours for small particles (r = 0.13-0 .25 mu m). Although some refinements are required for the model, it fo rms the basis for comparing the simulations with long-term atmospheric sea-salt measurements made at marine baseline observatories around th e world and for a more comprehensive three-dimensional modeling of atm ospheric sea-salt aerosols.