# Possible Missing Sources of Atmospheric Glyoxal Part I: Phospholipid Oxidation from Marine Algae
## 1 Introduction  
Glyoxal, the smallest of \(\alpha\)-dicarbonyl compounds, is a ubiquitous gas-phase oxidation product of a variety of volatile organic compounds (VOCs) found in the atmosphere. The vast majority of research has focused on elevated glyoxal concentrations in urban environments as a result of vehicle emissions, in addition to other anthropogenic sources including biomass and fossil fuel burning [1; 2; 3; 4; 5; 6; 7; 8]. The largest known precursor for glyoxal is isoprene, which is emitted from terrestrial biogenic sources and, to a much lesser extent, from the oxidation of monoterpenes [9; 10; 11; 12; 13]. Interest in the origins and levels of glyoxal within the atmosphere lies in its potential contribution to aerosol particles that serve as cloud condensation nuclei, which is one of the most poorly understood topics in atmospheric aerosol research [14]. Given the highly water-soluble nature of glyoxal, it readily uptakes water to form aqueous particles (i.e., aerosols, fog, or cloud droplets) where it can be oxidized [15], form oligomers [16], and react with salts [17] and organics [18; 19; 20] to form secondary organic aerosols (SOA) [9; 21; 22; 23]. It has been shown that sulfuric acid-catalyzed heterogeneous reactions involving glyoxal and other aldehydes can lead to the growth of newly nucleated nanoparticles [24; 25; 26; 14]. Moreover, aqueous-phase processing of glyoxal can result in a range of light-absorbingmolecules [17; 18; 19; 27; 28; 29; 30]. Thus, SOA is one of the greatest points of uncertainty in estimating aerosols' impact on climate [31; 32]. Glyoxal's relevance to atmospheric chemistry and climate change comes from its role in secondary organic aerosol formation, its involvement in oxidative processes, its impact on the global carbon cycle, and its effects on cloud formation and radiative balance. In urban areas [6; 8; 23] and forest environments [10; 11] reported glyoxal levels range from a few hundred parts per trillion (pptv; pmol/mol) to low thousands of pptv using ground-based instrumentation [33]. Satellite observations have given similar trends of elevated concentrations over these regions [34; 35; 36]. A number of marine glyoxal measurements have also been reported, but these values are far less consistent. [PERSON] et al. (2014) calculated eddy covariance measurements of glyoxal and found average mixing ratios of 43 \(\pm\) 9 pptv and 32 \(\pm\) 6 pptv in the Southern and Northern hemispheres, respectively, which were collected during a cruise using fast light-emitting diode cavity-enhanced differential optical absorption spectroscopy (Fast LED-CE-DOAS) [37]. Based on 10 field campaigns across the world's oceans employing multiaxis (MAX) DOAS and long-path DOAS, similar concentrations of approximately 25 pptv with an upper limit of 40 pptv within the marine boundary layer (MBL) have also been calculated [33]. Most recently, [PERSON] et al. (2015) noted seasonal in situ mixing ratios of 7 ppt (winter) and 23 ppt (summer) over temperate ocean waters based on 2,4-dinitrophenylhydrazine derivatization of glyoxal and ultraviolet (UV) detection [38]. Although the summer mixing ratios are in good agreement with the MAX-DOAS values, overall, these findings are much lower than reported by [PERSON] et al. (2010), where glyoxal levels were found to reach 140 pptv based on comparable spectroscopic analysis [39]. Satellite measurements made over open topic waters extrapolated glyoxal concentrations in excess of 200 pptv [34; 35], which is inconsistent with atmospheric models that predict trace levels in these isolated regions [9; 13; 40]. The literature indicates that models underestimate glyoxal production, particularly in urban and remote regions. This underestimation is likely due to the incomplete representation of volatile organic compound (VOC) oxidation pathways in current models, including those from biogenic and anthropogenic sources.