Sample Collection
Aerosol samples were collected on acid-washed Whatman 41 (W41) cellulose ester filter papers deployed in one of two high-volume aerosol samplers (model 5170-VBL, Tisch Environmental) simultaneously operating at approximately 1.2 cubic meters air per minute. The aerosol samplers were deployed on the ship’s flying bridge (14 m above sea level) as high off the water as possible. Contamination from the ship’s stack exhaust was avoided by controlling aerosol sampling with respect to wind sector and wind speed using an anemometer interfaced with a Campbell Scientific CR800 datalogger and PC. The samplers were allowed to run when the wind was +/- 60 degrees from the bow and > 0.5 m/s. When the wind failed to meet these two criteria, the motors were shut off automatically and not allowed to restart until the wind met both the speed and direction criteria for 5 continuous minutes. The anemometer was deployed nearby on a separate pole in 'free air' where turbulence from the wind crossing the bow did not cause the wind vane to wobble excessively.

Trace Element Determination
The fractional solubility of aerosol trace elements was estimated using the flow-through deionized water leaching protocol of Buck et al. (2006), conducted under a Class-100 laminar flow hood within 1 week of sample collection. Ultrapure deionized water (100 mL, >18 MΩ cm resistivity, pH ~ 5.5, Barnstead Nanopure) was rapidly passed through an aerosol-laden W41 filter held in a polysulfone vacuum filtration assembly (Nalgene). Operationally defined dissolved (≤0.45 um) trace elements were collected in the filtrate (leachate) by positioning a GN-6 Metricel backing filter (cellulose esters) below the aerosol-laden W41 disc in the filtration assembly. Ninety mL of the leachate was immediately transferred into an acid-cleaned 100 mL low density polyethylene bottle and acidified to ~0.024 M HCl (pH ~ 1.7) with ultrapure HCl and double-bagged for storage until analysis. Filters for both the soluble aerosol concentration measurements were stored frozen prior to performing the leaches. Trace element concentrations in the leachate solutions were determined by inductively coupled plasma mass spectrometry (Thermo Element-2) at the National High Magnetic Field Laboratory at Florida State University. Blank solutions were prepared by passing 100 mL of deionized water through W41 filters that had been deployed in the aerosol sampler while not in operation for 1 h. Blank leachates averaged e.g., 0.007 ± 0.004 pmol dissolved Fe and 0.073 ± 0.007 pmol dissolved Al (representing averages of 1.6 ± 0.38% and 9.1 ± 0.40% of the Fe and Al sample concentrations, respectively), and were subtracted from all leachate sample concentrations. Analysis of replicate filters for soluble Fe and Al produced relative standard deviations of 10% and 11%, respectively.

Major seawater anion determination
Following the DI water leach a 10 mL aliquot was taken for determination of DI soluble Cl-, NO3- and (SO4)2-. The aliquot was decanted into 15 mL HDPE bottles, double-bagged and immediately frozen at -20 degrees C for sample preservation and storage. Prior to major anion determination by ion chromatography (Dionex), samples were left to defrost at room temperature. Non-sea salt sulphate (nss-(SO4)2-) was calculated using the concentration of DI water soluble Na (as determined by ICP-MS, see above) as the reference element to correct for aerosol sea spray content. The following equation was used:

nss-(SO4)2-= (SO4)2-measured−[( (SO4)2-/Na)seawater* (SO4)2-measured]

References:
Buck, C. S., Landing, W.M., Resing, J. A., Lebon, G. T. 2006. Aerosol iron and aluminum solubility in the northwest Pacific Ocean: Results from the 2002 IOC cruise. Geochemistry, Geophysics, Geosystems. 7. doi:10.1029/2005GC000977.

GT10-11_Aerosols_DI_Soluble_joined.csv