Bulk primary marine aerosol (PMA) samples for major inorganic ion analysis were produced from Sargasso seawater using a high-capacity marine aerosol generator (see Frossard et al. 2019 for detailed design of the PMA generator). In addition to bulk PMA samples, which contained particles of all sizes produced by the generator, a Micro-orifice Uniform Deposit Impactor (MOUDI) sampler was used once during each cruise to collect a dichotomous PMA sample with two particle size fractions; a submicron fraction with particle sizes ranging from <0.18 to 1 µm and a supermicron fraction with particles ranging from 1 to >10 µm in diameter. All PMA were produced by pumping near-surface seawater (ca. 5 m) continuously through the generator at a flow rate of 4 liters per minute and bubbling this seawater with air. The air was introduced through a venturi tube to generate a bubble spectrum approximating that generated from a breaking wave. Bulk PMA samples for major ions were collected on pre-combusted 47-mm diameter quartz fiber filters at the aerosol generator air sampling rate of 30 liters per minute and a sampling time of approximately 24 hours; a quarter of each PMA sample filter was stored in a Simport cryovial in a freezer for further analysis. Dichotomous samples were collected for 48 hours at a flow rate of 30 liters per minute; submicron particles were collected on a pre-combusted 37 mm diameter quartz filter, and supermicron particles were collected on a pre-combusted 47 mm diameter quartz filter.

A separate BCO-DMO dataset is available for the seawater samples that were collected on the two cruises for major ions. These samples (ca. 7 mL of unfiltered seawater) were collected into high-density polyethylene (HDPE) vials and stored frozen until analysis. (See "Related Dataset" section below for details).

To process the samples, 5 mL of high purity laboratory water (Milli-Q brand water) was added to each Simport vial containing a PMA sample filter followed by alternating steps of vortexing (5 min) and sonicating (5 min) three times. Each processed sample was filtered into another clean cryovial using a 0.22 µm acetate glucose syringe filter and a plastic syringe. Aliquots of the filtered samples were diluted in Milli-Q water for ion chromatographic analysis.

Seven major ionic species were analyzed using the method outlined in Keene et al. (2007). A Dionex dual channel model ICS 6000 high-performance ion chromatograph (ICS-6000 DP) was used to perform sample analysis. The anion channel was configured with Thermo Scientific Dionex guard (IonPac AG 18: 4 x 50 mm). The cation channel was configured with Dionex Guard (IonPac CG12 A: 4 x 50mm) and analytical (IonPacCG12A: 4 x 250mm) columns and a Thermo Scientific Dionex electrolytically regenerated suppressor (ADRS 600: 4mm). The ion chromatograph was equipped with a Dionex AS-AP autosampler with the temperature set at 20°C, eluent generator cartridges (500 MSA, 500 KOH), ICS-6000 pumps, and Chromeleon 7 software.