Near-surface aerosol transmission in the marine environment

An extensive data set of aerosol vertical concentration profiles (height range 0.5-15 meters, diameter range 10-75 micron), acquired with the Rotorod(3) device at various geographical locations has been statistically analyzed. The analysis supplied a parameterization for the 4(th) (large particle) lognormal mode in the Advanced Navy Aerosol Model (ANAM). The analysis revealed a positive correlation between concentration and wind speed, and a negative correlation between concentration and height. No clear dependence of radius and width on meteorological parameters has been found. Numerical simulations with the Dutch-French SeaCluse model supported the results of the statistical analysis. The present version of ANAM predicts the experimental aerosol concentration to within a factor of 3. This result was confirmed using an independent data set. Initial extinction calculations with the ANAM indicate that the addition of the 4(th) mode changes aerosol extinction values by about 20% as compared to NAM calculations. Closer to the surface, this number is even higher due to the height dependence of the 4(th) mode.