[A-AS11] Atmospheric Chemistry

[AAS11-10] Characterization of aerosol number size distributions and their effect on cloud properties at Syowa Station, Antarctica

*Keiichiro Hara¹, Chiharu Nishita-Hara², Kazuo Osada³, Masanori Yabuki⁴, Takashi Yamanouchi⁵ (1.Fukuoka University, 2.FITEH, Fukuoka University, 3.Nagoya University, 4.RIHS, Kyoto University, 5.National Institute of Polar Research)

Keywords:Aerosols, Antarctica, New particle formation, Ozone hole

Aerosol measurements were conducted at Syowa Station, Antarctica in 2004–2006 to characterize the aerosol number–size distribution and other aerosol physicochemical properties. Aerosol number–size distributions were classified into four modal structures (i.e., mono-, bi-, tri-, and quad-modal) during measurements. Because the smallest mode of tri-modal and quad-modal structures appeared in nucleation mode, tri-modal and quad-modal structures were associated with new particle formation (NPF). We compared the aerosol size distributions and modal structures to air mass origins computed using backward trajectory analysis, in order to elucidate where NPF proceeds in the Antarctic. Results of the comparison imply that aerosol size distributions related to fresh NPF (quad-modal distributions) were observed in coastal and continental free troposphere (FT; 12% of days) areas and marine and coastal boundary layers (1%) during September–October and March, and in coastal and continental FT (3%) areas and marine and coastal boundary layers (8%) during December–February. With the existence of the ozone hole in the Antarctic stratosphere, more UV radiation can enhance atmospheric chemistry to form aerosol precursors, even in the Antarctic troposphere. However, linkage among tropospheric aerosols in the Antarctic, ozone hole, and UV enhancement is still unknown. Our results demonstrated that NPF started in the Antarctic FT already at the end of August – early September by UV enhancement resulting from the ozone hole. Then, aerosol particles supplied from NPF during periods when the ozone hole appeared to grow gradually by vapor condensation, suggesting modification of aerosol properties such as number concentrations and size distributions in the Antarctic troposphere during summer. Here, we assess the hypothesis that UV enhancement in the upper troposphere by the Antarctic ozone hole modifies the aerosol population, aerosol size distribution, cloud condensation nuclei capabilities, and cloud properties in Antarctic regions during summer.