Chemical characterization of marine aerosols and their impacts on climate system

Abstract

In the last decade, atmospheric aerosols have attracted considerable attention due to their impact on global climate change. Since 1994, the author has been working on the chemical characterization of marine aerosols over the western North Pacific Ocean, and investigated their physical and chemical properties, spatial and temporal distributions, transport processes, and contributions to cloud condensation nuclei (CCN). From an analysis of long-term observations at Haha-jima Island, the author found that water-soluble organic species are important constituents of CCN in the remote marine atmosphere, and play a key role in cloud formation and indirect radiative forcing processes. Continental outflows cause higher CCN densities and influence the optical properties of clouds over the remote ocean. In addition, the author determined the concentrations of the main chemical components in marine aerosols and their seasonal characteristics over this oceanic region. Higher concentrations of non sea-salt sulfate (nss-SO₄^2-), nitrate (NO₃^-), ammonium and oxalate were found in the continental air masses, whereas formate and acetate showed seasonal trends associated with marine biospheric activities. In simultaneous observations on four islands around Japan, the author clarified the spatial distribution, source regions, transport mechanism, and transport pathway of land-derived aerosols over the western North Pacific Ocean. For example, mineral particles are an important carrier for acidic species, especially for NO₃^-, over the seas close to the continent, whereas sea-salt particles act as a significant sink for these species over the remote ocean. Carbonaceous species were affected by biomass burning sources. The atmospheric behaviors of nss-SO₄^2-, NO₃^-, and carbonaceous species are different from each other, although they are all mainly derived from combustion sources.