The total aerosol optical depth p is the sum of three components: the stratospheric, us; the upper tropospheric um and the marine boundary layer, um. The extinction coefficient at the sea surface ao can be calculated from ao = f(u-us-um)/h, where h is the height of the boundary layer and f is a factor that accounts for the height dependence of aerosol extinction in the boundary layer. A boundary layer aerosol model is presented that explains the height dependence of a. Both f and h depend on the general synoptic weather pattern. This is demonstrated using a set of aircraft aerosol profiles measured over the Pacific Ocean in the vicinity of Monterey, California.