Dataset: GP15 SMLH2O Aerosol Ions Leg 2

A total of 11 48-hour integrated aerosol samples were collected during Leg 2 of the US GEOTRACES Pacific Meridional Transect research cruise (GP15), which took place on the RV Revelle (cruise RR1815) during October-November 2018. The cruise track consisted of a southward transect across the Pacific Ocean between Hawaii and Tahiti. See attached Supplemental File of sample locations (.png).

Bulk aerosol samples for major ion analyses were collected using one of five Tisch Environmental high-volume (~1 m³ air min⁻¹) aerosol samplers (model 5170V-BL). For each deployment, 12 replicate 47 mm diameter Whatman 41 filters were loaded on open-face filter holders (Advantec MFS installed on the aerosol sampler on a PVC adaptor plate (Shelley et al., 2015). Filters were acid-washed before use to reduce trace element blanks, following the procedure described by Morton et al. (2013). The samplers were deployed on the forward rail of the ship’s 03 deck approximately 16m above sea level, to minimize the influence of sea spray on samples. Samplers were controlled by wind speed and direction, through a Campbell Scientific CR800 data-logger interfaced with an anemometer and wind vane set up in close proximity to the samplers, in order to eliminate contamination from the ship’s stack exhaust. This setup was used to restrict sampling to periods when relative wind speed and direction were >0.5 m s⁻¹ and from within ±60° of the bow of the ship, respectively, for at least five continuous minutes.

Following sampling, the filters were transfer to pre-labeled petri slides. A set of filters from each deployment were "instantaneously" leached with ultrahigh purity (>18 MΩ∙cm; UHP) water according to the methods in previous studies (Buck et al., 2006; Morton et al., 2013). Other filters were transferred to petri-slides and stored frozen until trace element processing back on land. Approximately 30 mL from each leach was collected in an LDPE bottle to serve as a subsample to be analyzed for major ions. This subsample was stored frozen in a commercial freezer until analysis.

The concentration of the major cations and anions were analyzed by ion chromatography (IC) on a Dionex ICS-2100 instrument. The concentrations of the ions were calculated by linear regression of the system response to a series of standards of known concentration. Analytical accuracy was confirmed by regular analysis of check standards. All standards were made with ACS certified salts in UHP. Ion concentrations for each collection were normalized to pmol m-3 by dividing by the volume of air sampled.