Optical Properties of Aerosols in the Marine Boundary Layer during a Cruise from Tokyo, Japan to Fremantle, Australia.

Abstract

Shipboard aerosol measurements in the marine boundary layer (MBL) were carried out over the western Pacific Ocean through the eastern Indian Ocean during a cruise of the Antarctic research vessel Shirase from Tokyo, Japan to Fremantle, Australia in November 2000, as part of the 42nd Japanese Antarctic Research Expedition (JARE42) activities. The latitudinal variation of aerosol optical properties is investigated with the origin of aerosols. For elucidation of aerosol properties, a method for retrieving the complex refractive index from combined measurements is proposed using an optical particle counter, an integrating nephelometer and a particle soot absorption photometer. Backward trajectory analyses indicate three regions that are characterized by three distinct aerosol types: anthropogenic/continental aerosols (30°-33.5°N), maritime aerosols (3°-28°N), and biomass-burning aerosols (12°-2°S). Retrieval of the imaginary part of the complex refractive index is successfully achieved by the proposed method, resulting in mean values of 0.0056, 0.0003, and 0.0036 for anthropogenic/continental, maritime, and biomass-burning aerosols, respectively.