HR: 1340h
AN: A53A-0146    [Abstracts]
TI: Relationship Between Hygroscopicity and CCN Activity for Urban Aerosol Particles
AU: * Mochida, M
EM: mochida@lowtem.hokudai.ac.jp
AF: Institute of Low Temperature Science, Hokkaido University, N19, W8, Kita-ku, Sapporo, 060-0819 Japan
AU: Kuwata, M
EM: kuwata@atmos.rcast.u-tokyo.ac.jp
AF: Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904 Japan
AU: Miyakawa, T
EM: miyakawa@atmos.rcast.u-tokyo.ac.jp
AF: Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904 Japan
AU: Takegawa, N
EM: takegawa@atmos.rcast.u-tokyo.ac.jp
AF: Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904 Japan
AU: Kawamura, K
EM: kawamura@lowtem.hokudai.ac.jp
AF: Institute of Low Temperature Science, Hokkaido University, N19, W8, Kita-ku, Sapporo, 060-0819 Japan
AU: Kondo, Y
EM: kondo@atmos.rcast.u-tokyo.ac.jp
AF: Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904 Japan
AB: As described by the Köhler theory, hygroscopicity of atmospheric aerosol particles is one of the important factors governing their cloud condensation nuclei (CCN) activity. In this study, we investigated relationship between hygroscopicity and CCN activity for urban aerosol particles using a hygroscopicity tandem differential mobility analyzer (HTDMA) coupled to a CCN counter in series (HTDMA-CCNC system). The HTDMA-CCNC system was operated at RCAST, The University of Tokyo (located at the center of the Tokyo metropolitan area) from 8 to 17 November 2004. For aerosol particles whose dry mobility diameters are 30, 50, 80, 100, 150 and 200 nm, ratios of CCN to condensation nuclei (CN) at 0.21-1.2% supersaturation were obtained as a function of particle hygroscopicity under RH conditions of 83 and 89%. It has been clearly shown that more-hygroscopic particles behave as CCN more preferentially than less-hygroscopic particles, indicating that hygroscopicity of particles, in addition to their size, is a critical factor regulating the CCN activity. The obtained relationship between hygroscopicity and CCN activity was evaluated quantitatively by a model based on the classical Köhler theory. Some fraction of measured CCN is not predicted by the Köhler model, in the case that the surface tension under the supersaturation conditions is assumed to be equal to that of pure water. This suggests that CCN activity is enhanced by reduction of surface tension due to organics and/or by dissolution/dissociation of water-soluble organics under the supersaturation conditions. These effects originating from organics are probably important for CCN numbers and thus for cloud processes under various atmospheric conditions.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005