To assess whether atmospherically relevant chemical reactions are accelerated or inhibited by pressure, we performed a systematic screening of aerosol-phase chemistry. Solutions containing pairs of relevant reactants were exposed to pressures corresponding to aerosol diameters of 5–80 nm, enabling efficient identification of reactions influenced by Laplace pressure. All experiments followed protocols established in our preliminary glyoxal–ammonium sulfate studies.
In parallel, we developed a high-pressure reactor that enables real-time monitoring of reactant evolution via in situ UV–Vis absorbance at pressures from 1 to 1,000 bar and room temperature. The system combines a pressurization unit with an optical module for reaction monitoring under pressure. Using this approach, we investigated a broad range of atmospherically relevant reactions, including aldol and Baeyer–Villiger reactions, radical propagation, imidazole formation, esterification, decomposition, Diels–Alder reactions, and (photo)sensitized photochemistry. For each system, pressure-dependent kinetics, product distributions, and reaction mechanisms were characterized under atmospherically relevant conditions.
In parallel, we developed analytical capabilities to chemically characterize aerosol particles smaller than 100 nm using extractive electrospray ionization (EESI). EESI introduces analytes directly into a solvent spray, eliminating filter collection and minimizing fragmentation and thermal decomposition. Recent inlet optimization has significantly improved sensitivity (ng m⁻³) and time resolution (~1 Hz). To overcome limitations of prior EESI–TOF implementations, we developed a next-generation EESI source coupled to an Orbitrap mass spectrometer, enabling real-time, near-molecular-level aerosol characterization with detection limits of tens of ng m⁻³, linearity up to hundreds of μg m⁻³, and a time resolution of 0.2 Hz. System performance was validated using laboratory-generated secondary organic aerosol and ambient particle extracts, demonstrating robustness for resolving the composition of newly formed aerosols as a function of particle size and growth.
Finally, understanding aerosol growth requires simultaneous characterization of gas- and particle-phase composition to distinguish formation pathways. To this end, we conducted a 10-week laboratory campaign at the Paul Scherrer Institute, deploying multiple mass spectrometers (two Orbitraps and three time-of-flight instruments) to measure gaseous and particulate species in parallel. Monoterpenes and naphthalene were used as initial model precursors, followed by increasingly complex mixtures. Experiments were performed in a steady-state atmospheric simulation chamber with continuous reactant and oxidant input. Oxidation by ozone and/or OH radicals produced a wide range of oxygenated volatile compounds, driving particle formation under controlled temperature and humidity. Aerosol size and composition were resolved in time, providing a dynamic description of the processes governing aerosol formation and growth.
