Sampling:
Aerosol samples were collected by a MICRO ORIFIFICE UNIFORM DEPOSIT IMPACTOR (MOUDI) (MSP Corporation, MN, USA) which was installed on the forward rail of Healy's flying bridge, ~23 m above sea level, to minimize the influence of sea spray. To minimize the potential for contamination from the stack exhaust, samplers were forward of the ship's stack and sampling was controlled by wind speed and direction, through a Campbell Scientific CR800 data-logger interfaced with an anemometer and wind vane set up near the samplers. Aerosol sampling was restricted to periods when in-sector conditions (defined as a relative wind direction from within ±60° of the ship's bow and a relative wind speed of >0.5 m s-1) persisted for at least five continuous minutes. The MOUDI impactor used Teflon filters for particle collection (Pall Corp., 47 mm diameter, 1 µm pore size), with a sampling flowrate of 30 L min-1. Both the MOUDI impactor and its pump were housed in enclosures to protect them from rain and sea-spray with an extension tube connected to the MOUDI inlet and extending from the enclosure. A rain shield was installed above the inlet. Due to the anticipated low dust conditions during GN01, and the relatively low frequency of in-sector wind conditions, sample collections lasted for an average of seven days.

Clean polyethylene gloves were worn for loading and unloading of sample filters, which were carried out underneath a high-efficiency particulate air (HEPA) filter blower within a plastic "bubble" clean area constructed in the ship's main laboratory. Filters were loaded onto the MOUDI impactor from labeled petri dishes using pre-cleaned Teflon tweezers and were transferred back to the same petri dishes after sample recovery. Filter holders were double-bagged for transfer between the ship's laboratory and the samplers. Deployment blanks were carried out using the same protocols, but with the pumps turned off. All sample and field blank filters were subsequently double-bagged and stored frozen until analysis.

Sampler Location: Flying deck, forward railings
Sampler Type: MICRO ORIFIFICE UNIFORM DEPOSIT IMPACTOR (MOUDI) (MSP CORP.,MN, USA)
Sampler Flow: 0.030 m3/min
Substrate Type: Pall corp. Teflon Filter, 47 mm discs (Teflon, 1um pore size)
Size Segregation Method: Size-segregated sample; 1um is used as a cut off size for COARSE and FINE particle sizes

Aerosol Sample Analyses:
Ionic species in aerosols were measured following the detailed procedures in Xu et al. (2013).

Aerosol samples were analyzed by ion chromatography (IC; Dionex IC-2000) to measure the concentrations of water-soluble anionic and cationic species (chloride, nitrate, sulfate, acetate, formate, oxalate, MSA, propionate and sodium, potassium, ammonium, calcium, magnesium) at Rutgers University Atmospheric Chemistry Laboratory. For anion analysis, an AS11 analytical column (2 × 250mm2, Dionex, particle size 13µm), KOH eluent generator cartridge (EGC II KOH, Dionex) and 25µl sample loop were employed, while for cations, a CS12A analytical column (2 × 250mm2, Dionex, particle size 8.5µm), 25 µL sample loop, and MSA generator cartridge (EGC II MSA, Dionex) were used, similar to Xu et al (2013). Briefly, a one-quarter subsample of each filter was submerged in 5 ml of 18.2 MΩ∙cm deionized water, ultra-sonicated for 40 mins in an ultrasonic bath and then allowed to sit in the deionized water for ~10 hours, before being filtered through a 0.22μm PTFE syringe filter. The instrument detection limits (calculated as 3.143×standard deviation of 7 replicates of the lowest standard solution) were 0.007ppm for propionate, 0.008ppm for acetate and formate, 0.018ppm for oxalate, 0.013ppm for sulfate, 0.007ppm for nitrate, 0.015ppm for chloride and 0.016ppm for MSA, and below 0.01ppm for major cations. The precision, as determined for a low concentration standard (0.05ppm, n=7, and presented as relative standard deviation), was within 8% for all the species analyzed.