Seawater Analysis by Ambient Mass Spectrometry-Based Seaomics and Implications on Secondary Organic Aerosol Formation

Abstract. A transmission mode-direct analysis in real time-quadrupole time of flight-mass spectrometry (TM-DART-QTOF-MS)-based analytical method coupled to multivariate statistical analysis was developed to interrogate lipophilic compounds in seawater samples without the need of desalinization. An untargeted metabolomics approach addressed here as seaomics was successfully implemented to discriminate sea surface microlayer (SML) from underlying water (ULW) samples (n = 22, 10 paired samples) collected during a field campaign at the Cape Verde islands in September–October 2017. A panel of 11 ionic species detected in all samples allowed sample class discrimination by means of supervised multivariate statistical models. Tentative identification of these species suggest that saturated fatty acids, peptides, fatty alcohols, halogenated compounds, and oxygenated boron-containing organic compounds may be involved in water-air transfer processes and in photochemical reactions at the water-air interface of the ocean. A subset of SML samples (n = 5) were subject to on-site experiments during the campaign using a lab-to-the-field approach to test their secondary organic aerosol (SOA) formation potency. Results from these experiments and the analytical seaomics strategy provide a proof of concept that organic compounds play a key role in aerosol formation processes at the water/air interface.