Sea Spray Aerosol Chamber Study on Selective Transfer and Enrichment of Free and Combined Amino Acids

Free (FAAs) and combined amino acids (CAAs) were investigated on size-resolved samples of nascent sea spray aerosol (SSA) particles generated during controlled laboratory experiments. Compared to seawater, the amino acids were strongly enriched on the SSA particles. The enrichment factors (EF aer ) on submicron SSA particles (EF aer∑FAA: 2.5 × 10 6 and EF aer∑CAA: 7.9 × 10 5 ) were 1–2 orders of magnitude higher than on supermicron ones (EF aer∑FAA: 1.0 × 10 5 and EF aer∑CAA: 7.3 × 10 4 ) and continuously increased toward smaller SSA particles. Molecular-level analysis showed that the more polar the FAAs, the more they are enriched on the SSA particles (especially FAAs with polar acid side chains, e.g., aspartic acid: EF aer of 5.8 × 10 6 ). Comparison of the amino acids present on nascent SSA with those present on ambient marine aerosol particles revealed a higher complexity of the amino acids of the nascent SSA, suggesting that atmospheric processes likely reduce the amino acid diversity. In addition, our results highlight that although almost all the amino acids studied are transferred to the atmosphere via bubble bursting under controlled conditions, two amino acids, γ-aminobutyric acid (GABA) and glycine likely have additional sources to the atmosphere. GABA is likely formed on ambient marine submicron aerosol particles to a large extent (35–47% of ∑FAA). Glycine likely originates from long-range transport processes or photochemical reactions, as discussed in the literature; however, our results highlight the potential for a direct oceanic source via bubble bursting (∼20% of ∑FAA). Overall, bubble-bursting-derived total amino acids made up 11–18% of the mass of dissolved organic carbon on the submicron SSA particles.