Suitability of high-volume aerosol samplers for ultra-trace aerosol iron measurements in pristine air masses: blanks, recoveries and bugs

Abstract. Atmospheric inputs of soluble iron (Fe) to the global ocean are an important factor determining marine primary productivity and nitrogen fixation. To investigate soluble aerosol Fe and fractional Fe solubility, marine aerosol sampling has been conducted from a number of platforms including aerosol towers, ship and buoy platforms. A number of these studies have used commercially available high-volume aerosol samplers to collect aerosols from large volumes of air. These samplers are attractive for sampling air from low Fe air masses since they can rapidly concentrate large volumes improving detection limits. Here we investigate the use of a high-volume sampler from the Cape Grim Baseline Air Pollution Station (CGBAPS), Tasmania, Australia to sample aerosol Fe from baseline Southern Ocean air-masses. The study followed the United States Environmental Protection Agency (EPA) standard for the sampling of ambient air using high-volume sampler, and the recommendations and protocols from GEOTRACES community for sampling, sample preparation and digestion of trace element aerosols. Analysis and inspection of exposure blank (one month exposure) filters for Fe, and other metals, revealed significant contamination resulting from passive deposition of local soil, plants and insects. The results of the study suggest that high-volume aerosol samplers may not be suitable for low concentration air masses over the Southern Ocean without some mechanism to hermetically seal the sampler when the baseline sampling criteria are not met.