Size segregated aerosol samples were collected during the OASIS (“Organic very short lived substances and their Air Sea Exchange from the Indian Ocean to the Stratosphere”) cruises (FS Sonne, SO234-2 & SO235) during 8 - 20 July & 23 July – 7 August 2014 in the southern Indian Ocean (~30 E - 75 E, 30 S – 5 N). The samples were collected by Birgit Quack of GEOMAR, Kiel, Germany. The aerosol sampler was situated on the roof of the ship's wheelhouse and was connected to an automatic wind sector controller to prevent contamination of the samples from the ship's stack. Most samples were collected using a Sierra-type cascade impactor to separate the aerosol particles at an aerodynamic diameter cutoff of 1 µm. Collection time for these samples varied between 27.7 and 46.9 hours. For one sample, 6 impactor stages and a backup filter were used to give more detailed information aerosol size distribution. This sample was collected over 91.7 hours. Samples were extracted with ultrapure water and the major ions Na+, NH4+, Mg2+, K+, Ca2+, Cl-, NO3-, SO42-, oxalate, Br- and methanesulfonate were determined by ion chromatography (IC). Total soluble iodine (TSI) was determined by inductively coupled plasma - mass spectrometry (ICP-MS) and iodide (I-) and iodate (IO3-) were determined by IC-ICP-MS. The dataset contains the atmospheric concentrations of all measured soluble major ions (in nmol/m³) and iodine species (in pmol/ m³).

Sampler Flow: 1 m³/minSubstrate Type: Glass FibreSubstrate Pretreat: Washed in ultrapure water and then ashed at 450C for 4 hoursSize Seg Method: Sierra type cascade impactor. For most samples stages 3 and 4 were used and combined during analysis to give a fraction with aerodynamic diameter > 1 µm (Size_fraction 3-4). Backup filter collected the < 1µm fraction (Size_fraction w). Stages 1-6 and backup (w) filter were used an analysed separately for sample 10.Method Publication: Yodle and Baker, Atmospheric Environment X, 1, 100009, (2019).DL Value: Where the detection limit applies, concentrations are quoted as less than the limit of detection; Example atmospheric detection limits (given in Comment below) have been calculated from analytical detection limits for an air volume of 2500 m³.