Sea spray aerosol (SSA), primarily formed through bubble bursting at the ocean surface, represents one of the largest natural sources of atmospheric aerosols. SSA particles influence Earth’s radiation budget directly by scattering shortwave solar radiation and indirectly by acting as cloud condensation nuclei. In addition, SSA particles play a key role in atmospheric chemistry by providing surfaces for heterogeneous and multiphase reactions, thereby altering the oxidative balance of the atmosphere. Despite their significance, characterizing the physicochemical properties of SSA remain challenging, as ambient measurements are often complicated by mixing with anthropogenic and other natural sources, even in remote marine environments. This limitation has motivated the use of laboratory experiments, where SSA can be generated under controlled conditions. However, discrepancies exist between the properties of laboratory-generated SSA and those of ambient marine aerosol. Understanding the causes of these differences, and whether they can be bridged, forms the central objective of this thesis.

To this end, we deployed a sea spray simulation tank to generate SSA and used a potential aerosol mass (PAM) chamber to simulate atmospheric aging. We coupled this setup with a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) with iodide as reagent ion and conducted a field campaign on Graciosa Island in the Azores archipelago (eastern North Atlantic). We analyzed the chemical composition of nascent (freshly generated) and aged SSA, comparing them at the molecular level to ambient marine aerosols.

This field study, which forms the basis for Papers II, III, and IV of this thesis, revealed that volatile organic compounds (VOCs) co-emitted with nascent SSA are primarily CHO and CHOF compounds, including fatty acids, carboxylic acids, and perfluorocarboxylic acids. We also detected gas-phase urea and dihydroxyurea, which may contribute to marine new particle formation (NPF). Our findings also indicate that the oxidative conditions in the PAM chamber are harsh and favor nucleation of the co-emitted gases over condensation onto existing particles. This was confirmed by the dominance of formic acid – a likely fragmentation product – in the gas-phase composition of aged SSA.

Importantly, this work provides the first evidence that SSA particles can serve as a source of gas-phase per- and polyfluoroalkyl substances (PFAS). This finding opens new avenues for investigating the volatilization of other low-pKa compounds that may partition into the gas phase under the acidic conditions typical of SSA particles. It suggests that SSA-mediated transport of such species could play a larger role than previously thought.

In addition, we examined the particle-phase composition of nascent and aged SSA, which were dominated by CHO and CHON compounds – likely fatty acids and amino acid derivatives – consistent with previous studies. Ambient marine particle-phase aerosols, however, were enriched in glyoxal and CHON compounds, likely products of photochemical aging.

Because CIMS was the main analytical tool used in this study, we also delved into developing a deeper understanding of the instrument and identified the key parameters that affects its sensitivity (Paper I). These parameters include reactor pressure, reactor temperature, sample gas temperature, and the voltage gradient in the ion optics downstream of the reactor. For a fixed reactor geometry, we demonstrate that maintaining uniform values for these parameters allows sensitivity, normalized to reagent ion, to serve as a fundamental and transferable metric. This approach could simplify calibration requirements and facilitate cross-study comparisons. Furthermore, we show that collision-limited sensitivity under such conditions can be translated across different reagent ions and polarities, laying the groundwork for future harmonization and parameterization efforts.

Taken together, this thesis deepens our molecular-level understanding of SSA and its role in atmospheric chemistry, with practical insights into how we can better measure and compare these complex systems in both laboratory and field settings.