Transport and chemical transformation of anthropogenic and mineral aerosol in the marine boundary layer over the western North Pacific Ocean

Abstract

To characterize the transport and chemical transformation of anthropogenic and mineral aerosols in the marine boundary layer over the western North Pacific, intensive observations of aerosol chemistry were conducted in the period from March to May of 2001 simultaneously on two remote islands, Hachijo and Chichi-jima, located about 300 kin and 1000 km south of Japan's main island, respectively. Mean concentrations of nss-SO42-, NO3-, NH 4+, and nss-Ca2+ in aerosols during this period were 3.61, 1.35, 0.83, and 0.36 μg m-3, respectively, at Hachijo and 2.18, 0.52, 0.50, and 0.08 μg m -3, respectively, at Chichi-jima. Most of the nss-SO 42 was associated with NH4+ in fine particles at both sites. In the coastal oceanic region, NO3- was adsorbed mainly on coarse mineral particles, indicating that mineral particles act as important carriers and sinks for NO3-. On the other hand, in the remote marine environment, NO3- was mainly associated with sea-salt particles. Thus sea-salt particles act as important sinks for NO3- over the remote ocean. Elemental carbon (EC) in fine particles exhibited mean concentrations of 0.27 and 0.18 μg m-3 at Hachijo and Chichi-jima, respectively, with higher concentrations at Hachijo due to the influence of anthropogenic sources. On the other hand, mean concentrations of organic carbon (OC) in fine particles were estimated to be 0.35 and 0.41 μg m-3 at Hachijo and Chichi-jima, respectively. The higher concentration of OC in the remote marine atmosphere of Chichi-jima was attributed to carbonaceous substances evolved at lower temperatures (<200°C), which are probably derived from en route production and/or oceanic emissions. Copyright 2004 by the American Geophysical Union.