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

Abstract

<p><strong>Abstract.</strong> 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.</p>

Marine organic matter in the remote environment of the Cape Verde islands – an introduction and overview to the MarParCloud campaign

“…21a; all data listed in Table S4). While comparable SML data are lacking for this oceanic province, our data are in range with previous reports for surface water of subtropical regions (Zäncker et al, 2018). A strong day-to-day variability of absolute cell numbers was partly observed (e.g., the decline between 25 and 26 September), but all these changes were found in both the SML and bulk water (Fig.…”

“…The coupling of the DART ion source to high-resolution instrumentation allowed for generating elemental formulae for unknown species, and tandem MS capability contributed to the identification process. Tentative identification of discriminant species and the analysis of relative compound abundance changes among sample classes (SML and bulk water) suggested that 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 (Zabalegui et al, 2019). These identifications (e.g., fatty alcohols) agree well with the abundance of lipids in the respective samples.…”

“…For a further OM characterization of SML and bulk seawater, an ambient MS-based metabolomics method using direct analysis in real-time quadrupole time-of-flight mass spectrometry (DART-QTOF-MS) coupled to multivariate statistical analysis was designed (Zabalegui et al, 2019). A strength of a DART ionization source is that it is less affected by high salt levels than an electrospray ionization source (Kaylor et al, 2014), allowing for the analysis of seawater samples without observing salt deposition at the mass spectrometer inlet, or having additional limitations such as low ionization efficiency due to ion suppression (Tang et al, 2004).…”

“…A strength of a DART ionization source is that it is less affected by high salt levels than an electrospray ionization source (Kaylor et al, 2014), allowing for the analysis of seawater samples without observing salt deposition at the mass spectrometer inlet, or having additional limitations such as low ionization efficiency due to ion suppression (Tang et al, 2004). Based on these advantages, paired SML-bulk water samples were analyzed without the need for desalinization by means of a transmission-mode (TM) DART-QTOF-MS-based analytical method that was optimized to detect lipophilic compounds (Zabalegui et al, 2019). An untargeted metabolomics approach, referred to as seaomics, was implemented for sample analysis.…”

“…To explore if marine air masses exhibit significant potential to form SOA, a Gothenburg potential aerosol mass reactor (Go : PAM) was used that relies on providing a highly oxidizing medium to reproduce atmospheric oxidation on timescales ranging from a day to several days in much shorter timescales (i.e., a few minutes). During the campaign, outdoor air and gases produced from a photochemical reactor were flowed through the Go : PAM (Watne et al, 2018) and exposed to high concentrations of OH radicals formed via the photolysis of ozone and subsequent reaction with water vapor (Zabalegui et al, 2019, and references therein). The aerosol particles produced at the outlet of the OFR were monitored by means of an SMPS, i.e., only size distribution and number concentration were monitored.…”