# Possible Missing Sources of Atmospheric Glyoxal Part I: Phospholipid Oxidation from Marine Algae
## 1 Introduction
Additionally, some studies suggest that secondary organic aerosol (SOA) formation mechanisms, heterogeneous reactions, and glyoxal's rapid atmospheric removal processes may not be fully captured. Other overlooked aspects include the complexity of multi-phase chemistry and uncertainties in emission inventories, which also contribute to discrepancies between modeled and observed glyoxal levels. In addition, the determination of glyoxal using Fast LED-CE-DOAS, MAX-DOAS, and long-path DOAS faces limitations due to variability in atmospheric conditions, sensitivity, and spatial resolution. Fast LED-CE-DOAS offers high temporal resolution but can suffer from short optical paths, limiting detection sensitivity in low-glyoxal environments. MAX-DOAS and long-path DOAS provide better spatial coverage but are more susceptible to interference from aerosols and other trace gases, which can complicate the accurate retrieval of glyoxal concentrations across varying atmospheric conditions. In remote ocean measurements, [PERSON] et al. (2010) ruled out transport of glyoxal or its precursors from anthropogenic and terrestrial sources due to the long travel time (>1 week) that the air mass required to reach their sampling location 3000 km off the coast [39]. Globally, glyoxal has an atmospheric lifetime of 2-3 h [9; 40] based on known sinks due to photolysis, reaction with hydroxyl radicals, and uptake into aerosols [23]. Similarly, isoprene has an estimated lifetime of 1-4 h over the ocean [41; 42; 43; 44]. Taking into account the aforementioned range of glyoxal levels, an average of 50 pptv isoprene in the atmosphere based on a handful of measurements made over ocean waters [45], and an estimation that nearly half of all glyoxal yields from the oxidation of isoprene [9], it has been suggested in numerous manuscripts that there exists a missing source of glyoxal, likely of marine origin, that is at least an order of magnitude greater that what is currently known [9; 33; 38; 39; 40]. In recent reports, [PERSON] et al. (2014) demonstrated that glyoxal can be formed as a secondary or tertiary lipid peroxidation product of polyunsaturated fatty acids (PUFA) [46]. Ozone was made to pass over a monolayer of linoleic acid (C18:2, \(\Delta\) 9,12) on artificial seawater or sea surface microlayer (SSML) water collected from the Pacific ocean, which was placed in a flow tube, and its products monitored on-line by proton transfer reaction mass spectrometry. The authors reported a yield of less than 1%, which they attributed to dissolution of glyoxal in the condensed phase due to its highly soluble nature ([PERSON]'s law constant, H\({}_{\text{eff}}\) = 4.19 \(\times\) 10\({}^{5}\) M/atm) [47]. Additionally, malondialdehydedehyde, an intermediate to ozone-produced glyoxal, has not been detected in the atmosphere. Based on these findings, the authors suggest that it is unlikely that this chemistry could promote a flux of glyoxal that is able to explain observed atmospheric concentrations. In this work, however, we used mass spectrometric analyses of nascent sea spray aerosols (SSA) and the SSML of a naturally occurring algal bloom isolated within an ocean-atmosphere laboratory system to show for the first time that appreciable levels of glyoxal can be produced. We provide evidence that, as the algae die during the bloom, their phospholipids are enriched in the SSML, especially within the foam, and undergo autoxidation thereby generating glyoxal as a degradation product. We postulate that the enrichment of organic matter in the SSML creates a hydrophobic environment that affects the solubility of glyoxal such that bubble bursting action from wave breaking facilitates its transport across the air-water interface. Based on these findings, we propose that enrichment occurring during the death phase of an algal bloom and subsequent degradation could potentially serve as an important and currently missing source of glyoxal in the atmosphere.