Observational Results On The Influence Of Surface Layer Stability And Inversion Entrainment On Surface Layer Marine Aerosol Number Density (1 Micrometer)

Abstract

Wind speed and relative humidity have been the physical variables used in empirical expressions for equilibrium marine aerosol distributions. Recent formulations, which include the role of hydrostatic stability because it influences turbulent transport and entrainment of clear air from aloft, are examined on the basis of 1 um radius aerosol number density values. The aerosol data were collected along with a quite complete meteorological data set in the Northeast Atlantic during the international Joint Air Sea Interaction Experiment (JASIN-78). The 1 um number density values are normalized for generation and relative humidity influences, and analyses are performed to gain reasonable assurance that the aerosol were of sea salt origin. A stability influence was observed in the normalized number density results, but it was less than that predicted by a flux-profile relationship in which the only removal velocity was the gravitational fallout rate. Better agreement occurs when the entrainment rate of overlying air into the boundary layer is added as a removal velocity. This indicates that entrainment of clear air from aloft dilutes the near surface marine aerosol number densities a measurable amount.