Observations of aerosol volatility and elemental composition at Macquarie Island during the First Aerosol Characterization Experiment (ACE 1)

A combined thermal/electron microscopy technique was used to analyze marine aerosol samples from Macquarie Island (54 degrees 30'S, 158 degrees 57'E), obtained during November and December 1995 as part of the First Aerosol Characterization Experiment (ACE I). The analyses were performed for two size fractions, 80 < D-p, < 200 nm and D-p, > 200 nm. Sulfate particles were primarily observed in the 80 < D-p, < 200 nm fraction and were deduced to be present also at smaller sizes from the volatile response of the aerosol. In two of the samples early in the experiment, sulfate particles appeared to be partially or fully neutralized, but the particles in later samples from clean marine air masses were more volatile, suggesting a sulfuric or methanesulfonic acid composition. Sea-salt particles dominated the number concentrations of particles with D-p, > 200 nm and also contributed significantly to the number concentrations in the 80 < D-p, < 200 nm fraction. Evidence for increased sea-salt number concentrations at higher wind speeds was found.