Ionic strength effects on the reactive uptake of ozone on aqueous pyruvic acid: Implications for air-sea ozone deposition

A vertical wetted-wall flow tube technique was used to explore the ionic strength effects at the air-water interface in mediating the sea-surface reaction between ozone (O3) and pyruvic acid (PA). The uptake coefficients of ozone on aqueous PA increase substantially with the concentrations of bromide (Br-) ions, clearly indicating that the dry deposition of ozone could be significantly enhanced due to the presence of carbonyl compounds such as PA at the bromide-rich sea surface. Based on the observed uptake coefficients, the estimated deposition velocity of ozone (100 ppb) for a nM range of PA concentrations is ~ 1 · 10-3 m s-1, which represents a significant contribution to the known deposition velocity of ozone at the sea surface. The analysis of reaction products by Ultra-High Resolution Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry suggests the formation of oligomers, during both the dark and light-induced heterogeneous reactions between gaseous O3 and PA occurring at the surface of a dilute aqueous phase (representative of cloud droplets). The chemical structure of the detected high molecular weight compounds is much more complex than the oligomeric species identified during the photolytic degradation of bulk aqueous PA alone.