Optical and chemical properties of marine aerosols over the central equatorial Pacific Ocean during the 2003 R/V Mirai cruise

[1] The optical and chemical properties of atmospheric aerosols were measured over the central equatorial Pacific Ocean (from 150°E to 160°W longitude, near the equator) during the R/V Mirai cruise of January 2003. In the area from 165°E to 160°W along the equator, concentrations of anthropogenic chemical components were low; the average concentration of nonsea salt sulfate was 0.28 μg m−3, that of vanadium was less than the detection limit, and those of elemental carbon and organic carbon were 0.009 and 0.09 μg-C m−3. The scattering coefficients were low (3.2 × 10−6 m−1 on average), and the absorption coefficients were also extremely low (0.06 × 10−6 m−1 on average). The mean value of single scattering albedo was 0.98, with a standard deviation of 0.01, indicating that the measured aerosols were transparent and had low variability. The measurement results suggest that nonsea salt sulfate and organic carbon were from natural sources. Sea salt particles and nonsea salt sulfate composed a large fraction (94%) of the water-soluble components of fine particles. Thus the water-soluble components and organic materials from natural sources were primarily responsible for the scattering of solar radiation. The measurement results give typical values of the optical and chemical properties of aerosols in the unpolluted central equatorial Pacific Ocean.