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Atmospheric sampling of aerosol was carried out from ships during four separate month-long research cruises over remote oceanic regions. Three cruises took place in the Arabian Sea, during the inter-, SW- and NE-monsoons. An additional cruise was focused on the tropical North Atlantic Ocean. Identical sampling techniques were employed for all cruises. One high volume dichotomous virtual impactor and two low volume collectors were used to collect aerosol particles for the quantification of trace metals, anions and major cations. Ferrous iron concentrations were determined immediately after sample collection on board the ship using a ferrozine extraction technique. Data were analyzed by principal component, enrichment factor and weighted multiple linear regression analyses.
The mineralogical composition of aerosol collected over the Arabian Sea reflected that of an average of the earth's crust, while over the Atlantic Ocean, shale appeared to best represent the sampled mineral dust. With exception of the SW-monsoon samples, which were characterized by weak continental influences, the aerosol samples contained excess water-soluble non-sea-salt calcium that appeared to be of crustal origin, in the form of CaCO[...] or CaSO[...].
Ferrous iron concentrations accounted for 0.3, 1.3, and 0.5% of the total observed Fe during the inter- and NE-monsoons over the Arabian Sea, and over the Atlantic Ocean, respectively. Absolute Fe(II) concentrations were determined at 5.2, 9.8, and 3.1 [...]g [...] for the corresponding seasons, with most of the Fe(II) (> 80%) present in the fine fraction. Fe(II) did not exhibit a simple relationship with any of the sources indicating the complexity of iron redox reactions is this system.
Non-sea-salt sulfate (NSS-SO[...]) sources were identified and quantified with the use of multiple linear regression analyses. Biogenically-derived [...] contributed significant amounts of NSS-SO42-, especially during the SW-monsoon, when anthropogenic sources were small. Biogenic SO[...]/methansulfonic acid (MSA) weight ratios were determined and found to be in agreement with reported literature values from pristine oceanic regions, varying from 6.8 at 24°C to 17.7 at 28.9°C
