Filter and impactor measurements of anions and cations during the First Aerosol Characterization Experiment (ACE 1)

During the First Aerosol Characterization Experiment (ACE 1), we measured the concentrations of aerosol non-sea-salt sulfate (NSS), methane sulfonate (MS), ammonium, sodium, nitrate, and a variety of other anions and cations from the National Center for Atmospheric Research C-130Q aircraft and the Cape Grim Baseline Air Monitoring Station. We used the data to test a variety of hypotheses concerning the sources and properties of aerosol in remote environments. We noted a large gradient in free tropospheric (FT) MS, with much more in the spring (southern) hemisphere, but FT NSS showed no latitudinal gradient. Most species had strong vertical concentration gradients, generally with more material near the biogenic sources of the marine boundary layer (MBL) than in the FT. During the Lagrangian experiments and in time series measurements at Cape Grim, we saw daytime increases of photochemically derived MS, with more constant or decreasing concentrations at night. NSS also increased in the daytime during the Lagrangian experiments. At Cape Grim, we were unable to account for the gravimetric mass of particles on impactor substrates using the measured ions, which implies that a substantial fraction of the aerosol at that location must be either organic or mineral matter. Our FT ratios of MS/NSS exhibited a strong latitudinal gradient, with the southernmost values similar to those found in Antarctic plateau snowfall.