OBSERVATIONS OF ORGANIC MATERIAL IN INDIVIDUAL MARINE PARTICLES AT CAPE GRIM DURING THE FIRST AEROSOL CHARACTERIZATION EXPERIMENT (ACE-1)

During the First Aerosol Characterization Experiment (ACE 1) field cam paign in November and December 1995, the particle analysis by laser ma ss spectrometry instrument was used to measure the composition of ambi ent particles in situ at Cape Grim, Tasmania, under various conditions ranging from clean marine air to moderately polluted air. Internal mi xtures of sea-salt compounds and organic species were detected in over half of the negative spectra during clean marine conditions and in ab out 62% of the negative spectra during polluted conditions. In clean m arine air masses, aerosol organics appeared to have two distinct sourc e mechanisms depending on the extent of aerosol aging. Organic peaks h ad a positive trend with sodium sulfate peaks, indicating that organic s and excess sulfate may accumulate in aged marine aerosol particles b y similar mechanisms. When the sodium sulfate content was low, iodine had a positive trend with organics, which is consistent with organics and iodine originating from the surface-active layer of the ocean and becoming incorporated into fresh marine particles by bursting bubbles. Based on limited laboratory calibrations, the average organic mass is estimated to be of the order of 10% of the sea-salt content and is co nsistent with some of the missing mass fraction for Cape Grim particle s (S. Howell et al., manuscript in preparation, 1997), which is the me asured difference between gravimetric and ionic mass.