Observations of the Aerosol Size Distribution and Condensation Nucleus Concentration at Macquarie Island, Tasmania, during ACE-1

S. M. Kreidenweis and F. J. Brechtel
Department of Atmospheric Science, Colorado State University,
Fort Collins, CO 80523

During the Aerosol Characterization Experiment 1 (ACE-1) measurements were made of the aerosol number size distribution (between 18 and 540 nm diameter (Dp)) and total aerosol number concentration (Dp > 3 nm and Dp > 12 nm) on Macquarie Island, Tasmania (54.5 S, 159E, 7 m ASL). Observations were compared to those from a southern hemisphere mid-latitude site (Cape Grim) and to sites on the Antarctic continent, and it was found that the average total number concentration (Dp > 12 nm) observed at Macquarie Island during baseline conditions (500 cm^-3) was similar to values observed during the same time of year at Cape Grim and coastal Antarctic sites and about two times those observed at South Pole station. The number size distribution at Macquarie Island was typically bimodal and very similar to that previously reported for Cape Grim but distinctly different from that reported for coastal and inland Antarctica.

Relationships between transport processes and the aerosol size distribution and total number concentration at Macquarie Island during baseline and continentally influenced conditions at this remote marine site were examined. Baseline conditions were observed twice as often as continentally influenced conditions over the study period. Correlations between the observed aerosol properties and air mass source region, back trajectories and cyclone activity, as well as local horizontal and vertical motions have been investigated. It has been found that the higher particle concentrations observed during continentally influenced conditions were primarily due to an increase in the concentration of particles with diameters smaller than 60 nm.