CCN property of Asian mineral dust particle

°°We investigate the CCN property and the hygroscopicity ¦Ê, defined by Petters and Kreidenweis (2007), of the certified reference materials for Asian mineral dust particles produced by Nishikawa et. al., (2000). The rotating brush disperser (Palas, Model RBG-1000) was used as dry particle generation. The dispersed particles were once stored in the aerosol buffer tank (600l volume) via two cyclones (50% cutoff diameter 2.5um and 1.0um), and then supplied to each instruments. The measurement of activation spectrum was conducted by measuring DMT-CCNC (DMT, Model CCN-2) and CPC (TSI, Model 3772). Since DMT-CCNC not only measures CCN number concentration but also droplet size distribution (DSD) which the particles were grown up by condensation growth, DSD in the size range of 0.75 to 10 um at setting supersaturation was also acquired. In the measurement of the hygroscopicity parameter ¦Ê, DMA (TSI, Model 3080), DMT-CCNC, and CPC were used. The particles selected by the DMA were simultaneously measured by CPC and DMT-CCNC. The activated particle fraction (Nccn/Ncn) was calculated from the concentrations of CN (Ncn) and CCN (Nccn), and a Nccn/Ncn over dry diameter was obtained from every scan of particle diameters at constant supaesaturation. Detailed information of this procedure is described by Koehler et. al., (2007) and Rose et al. (2008). The ratio of Nccn/Ncn at SS=0.2% and 0.4% was 0.6 and 0.8, respectively. Therefore, it is suggested that asian mineral dust efficiently act as CCN in the case of its only. The ¦Ê-value of Asian mineral dust was about 0.005. The ¨º-value of ATD was slightly higher than that of the referenced kosa particle. Koehler et al., (2009) reported the ¨º-value of dry ATD was 0.025.

°°We observed the CCN concentration and droplet size distribution using the DMT-CCNC during the dust event (17-20 March 2009) at Tsukuba (36.06°N, 140.13°E), Japan. This dust event was observed wide area of Japan. The result shows that the CCN concentration decreased and the mean volume droplet diameter increased by the coming of the dusty air mass. From the calculation of the diffusion growth using ¦Ê value estimated above, it is suggested the CCN fraction of Asian mineral dust particles was low during dust event which observed in 17-20 March 2009.