# Possible Missing Sources of Atmospheric Glyoxal Part I: Phospholipid Oxidation from Marine Algae
## 4 Conclusions  
This work represents the first measurements of glyoxal made on nascent SSA generated during a naturally occurring phytoplankton bloom within an ocean-atmosphere laboratory system. The data herein unequivocally show that the ocean can serve as a source of glyoxal in the atmosphere due to radical and ozone-initiated oxidation of phospholipids present in the SSML, especially the foam. These findings strongly suggest that glyoxal production is linked to marine microbiological activity based on the following proposed mechanism: Inorganic nutrients drive an algal bloom. When depleted, the phytoplankton die and become organic nutrients for the bacteria, which facilitate the decomposition of the algal cellular structure. As the membrane degrades, its phospholipids are enriched at the air-water interface due to the hydrophobic nature of the fatty acid chains. Given that algal phospholipids are rich with PUFAs, they are highly susceptible to oxidation. Degradation of the enriched oxidized phospholipids yield glyoxal along with other VOCs. Glyoxal transfer from the ocean into the atmosphere is aided by bubble bursting from breaking wave action and likely a critical OC level that changes the solubility conditions at the surface. Thus, the prolonged death phase of an algal bloom serves as an important and currently missing source of marine glyoxal in the atmosphere. This proposed mechanism provides a possible explanation for the large discrepancies in reported glyoxal concentrations measured over open waters. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/metabo14110639/s1](https://www.mdpi.com/article/10.3390/metabo14110639/s1)]([https://www.mdpi.com/article/10.3390/metabo14110639/s1](https://www.mdpi.com/article/10.3390/metabo14110639/s1)), Figure S1. Phytoplankton bloom conditions during IMPACTS (a), and in the coastal waters off of the SIO pier in La Jolla, CA, Figure S2. Schematic of the air scrubbing system and an impinger for the wave channel during IMPACT, Figure S3. GC/MS chromatogram of a quinoxaline standard, Figure S4. GC/MS chromatogram of FAME standards, Figure S5. GC/MS chromatogram of a benzimidazole standard, Figure S6. Equipments. Figure 6: GC/MS headspace analysis of the dose-dependent UV irradiation of C18:2 FAME standard (RT 21.5 min) (**a**) and the MS of hexanal which is an oxidation product of C18:2 (**b**) collected by SPME. **Author Contributions:** Conceptualization, R.T.W., R.S.P., K.A.P. and F.A. ; methodology, R.T.W., R.S.P. and K.A.P. ; validation, R.T.W. ; formal analysis, R.T.W., A.C.-B., N.S., R.S.P. (IMPACTS SPME, Culture Flasks, GC/MS), (IMPACTS impingers LC-ESI-MS/MS), C.M.S., J.L.A., K.A.M., M.V.S., C.L. (IMPACTS Chlorophyll a and Nutrients), F.M. and Y.Z. (IMPACTS Et Etchohydrolytic Chitinase and heterotrophic bacteria); resources, R.T.W., R.S.P. and K.A.P. ; data curation, C.M.S., C.L. (IMPACTS Chlorophyll a and Nutrients), R.T.W., A.C.-B., N.S. (IMPACTS SPME GC/MS), R.T.W., R.S.P. (Culture flask GC/MS), F.M., Y.Z. (IMPACTS Etchohydrolytic Chitinase and heterotrophic bacteria) and R.T.W. (IMPACTS impingers LC-ESI-MS/MS); writing--original draft preparation, R.T.W. ; writing--review and editing, R.T.W. and R.S.P., visualization, R.T.W. and R.S.P. ; supervision, R.S.P., K.A.P. and F.A. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by NSF CCI grant number 1305427, National Science Foundation: CHE-1801971 and UC President's Postdoctoral Fellowship Program. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy. **Conflicts of Interest:** The authors declare no conflicts of interest.