12:00 PM - 12:15 PM
[ACG52-12] Size distributions and CCN activities of marine aerosols obtained in the longitudinal observation over the Pacific Ocean
Atmospheric measurements were conducted during R/V Hakuho-maru KH-13-7 and leg 2 of KH-14-3 cruises. Ambient air was sampled continuously through the inlets via silicon tubing and then dried with a diffusion dryer. The dried air samples were introduced to a scanning mobility particle sizer to measure number size distributions of the ambient aerosols. CCN concentrations were measured with a continuous flow thermal gradient CCN counter during the leg 2 of KH-14-3. Concentrations of atmospheric trace gases (O3 and CO) and radon daughters, those can be tracers for land-origin and/or anthropogenic air masses, were also measured continuously along the cruise tracks.
The aerosol number concentrations varied from <100 to 3000 cm-3 and the spatial variations could not be explained only by the transport of land-origin air masses. This result suggests that it is necessary to consider the supply of marine origin material to the atmosphere. The aerosol number size distributions showed bimodal with a gap around 100 nm in diameter, which is characteristic of clean maritime air, in most of the oceanic region. The Aitken mode (diameter less than 100 nm) contributed greatly to the number of aerosols in the regions where the influence of land-origin air masses were small, indicating that the regions were suitable for the condensation and growth of fresh particles. Actually, a few typical events of new particle formation were observed in the South Pacific. In the arctic region, a spontaneous enhancement of aerosols with diameter around 100 nm was observed. Because there were not major anthropogenic sources of pollutants around the arctic region, the enhanced particles might be come from biogenic sources. Analysis based on CCN activation ratio suggests that these increased fine particles were rich in organics.