11:45 AM - 12:00 PM
[ACG52-11] Number-size distribution and cloud condensation nuclei (CCN) activity of marine aerosol over the northern North Pacific in spring
The atmospheric observation on R/V Hakuho-maru was performed from 6 to 26 March, 2015. Aerosol particles passed through a cyclone (50% cut-off diameter: 2.5 micrometer) were introduced to the instruments in the laboratory, and the number-size distribution of the aerosol was measured every 5 min using a scanning mobility particle sizer. Further, the CCN efficiency spectra (the ratios of CCN to aerosol particles at respective diameters) at 0.1%, 0.2%, and 0.6% supersaturations were also measured every 1 h using a scanning mobility CCN analysis system, by switching the supersaturation conditions every 20 min.
The number-size distribution was bimodal on the average. Based on the characteristics, the observed aerosols are categorized to 3 types: (a) the number concentration was low and the peak of the size distribution was in the accumulation mode (diameter: >100 nm); (b) the number concentration was high and the peak of the size distribution was in the Aitken mode (diameter: <100 nm); (c) peaks were both in the Aitken and accumulation modes. Based on the backward trajectory analysis of the studied air masses, it is inferred that the transport of terrestrial aerosols in addition to clean maritime aerosols affected the number-size distributions. The hygroscopicity parameter calculated from the CCN efficiency spectra were lower than literature values for clean marine aerosols enriched in inorganic salts. This result suggests that the presence of organic components of terrestrial origin or those from the sea surface resulted in the decrease of the CCN activity of aerosol particles. The CCN number concentrations tended to be high, as compared to literature values for the clean marine atmosphere. The obtained data would be useful to assess the contributions of marine biota to the CCN number concentrations and those of physical factors (the number concentration and number-size distribution) and chemical factors (the chemical composition and hygroscopicity) to the CCN concentrations.