Abstract
Size distributions and optical thicknesses of aerosols were measured with the particle counter and the sunphotometer respectively on an aircraft and at the surface. The optical thickness was calculated from measured size distributions and compared with that observed with the sunphotometer. For the aircraft measurements, the optical thickness was determined for refractive indices 1.4, 1.5, 1.595 and 1.5-0.01i from the counter measurements and com-pared with the observed values. The result showed that the observed and the calculated optical thicknesses at 500nm were in fairly good agreement, even though it depended on the refractive index. A mixing layer was observed during the aircraft measurements and the aerosol optical thickness at the top of this layer decreased to about one tenth of that at the surface, so the aerosols in the mixing layer account for the greatest part of the contributions to the optical thickness at the surface. From the observed aerosol concentration at the surface and the aerosol vertical profile given by Elterman, the optical thickness at the surface was also determined and compared with the observed values. The ratio of the calculated optical thickness to the observed at the surface was close to unity for neutral conditions. But the calculated value was larger and smaller than the observed for stable and unstable conditions, respectively.
