A M Middlebrook,* D M Murphy, and D S Thomson* (NOAA Aeronomy Laboratory, 325 Broadway, R/E/AL6, Boulder CO 80303; *also at University of Colorado, CIRES, Boulder, CO 80309; 303-497-7324; amiddlebrook@al.noaa.gov)
During the Aerosol Characterization Experiment (ACE-1) field campaign in November and December, 1995, the PALMS (Particle Analysis by Laser Mass Spectrometry) instrument was used to measure the composition of ambient particles at Cape Grim, Tasmania. This instrument is capable of obtaining negative or positive mass spectra in real time of individual aerosol particles with diameters greater than 0.16 microns. Our aerosol inlet was positioned roughly 130 m above sea level on a communications tower about 120 m inland from the Indian Ocean. During the campaign, we collected over 20,000 individual particle spectra under various conditions ranging from very clean, marine air to polluted air from rural and urban locations.
Because spectra were obtained from individual particles, we can distinguish internal mixtures from external mixtures. The particle mass spectra indicate that more than 98% of the particles during all conditions contained detectable amounts of sea salt compounds such as Cl, Na, Mg, sulfate salts, Ca, K, Br, Sr, and H2O. Of these particles, more than 85% contained detectable amounts of other species. For example, internal mixtures of sea salt compounds and organic species were detected in 58% of the particles during clean, marine conditions and in 81% of particles during polluted conditions. On the average, the organic peaks in the sea-salt- containing particles were larger than peaks from nitrogen oxides, ammonium, sulfate, iodide, carbon clusters, or metals (Si, Al, Fe, Cu, Pb, Sn, Mo, and Cr) under all conditions. The significance of including organic material in particle mass balances of marine aerosols and possible incorporation mechanisms for organic material in marine aerosols will be discussed.