Atmospheric deposition fluxes and processes of the water-soluble and water-insoluble organic carbon in central Japan

Abstract

In order to investigate the wet and dry deposition fluxes of the water-soluble organic carbon (WSOC) and water-insoluble organic carbon (WIOC) and to clarify the factors influencing them, a simultaneous observation of the WSOC and WIOC in both the wet and dry deposition and in the aerosols was conducted for 2 years at an urban site in central Japan. The average deposition fluxes of the WSOC and WIOC by the wet process were 3.514 and 1.719 mgC m−2 day−1, respectively, and those by the dry process were 0.346 and 0.822 mgC m−2 day−1, respectively. About 82% of the organic carbon (OC) that is the sum of the WSOC and WIOC was deposited by the wet process. A large contribution of the wet process to the atmospheric deposition was found not only for the WSOC but also for the WIOC; the contribution of the wet process to the atmospheric deposition was about 91% for the WSOC and about 68% for the WIOC. About 67% of the OC in the wet deposition was explained by the WSOC, whereas about 70% of the OC in the dry deposition was by the WIOC. The WSOC in the coarse aerosols (d = 2.0–10 μm) in the surface atmosphere had a significant impact on the wet deposition flux of the WSOC. In addition, the length of the rainy period also strongly influenced the wet deposition flux of the WSOC. On the other hand, the WIOC in the wet deposition would be influenced by its concentration not only in the ground surface aerosols but also in the upper atmospheric aerosols. The dry deposition fluxes of the WSOC and WIOC were significantly affected by their concentrations in the aerosols with the diameters larger than 10 μm (PM>10). The dry deposition of the PM>10 aerosols in the surface atmosphere had a significant impact on the OC deposition by the dry process.