The ionic strength can affect the kinetics and products distribution within the aerosol deliquescent particles and at the sea surface microlayer. However, the ionic strength effects on aqueous phase reactions of atmospheric relevance have been barely studied in the past. In this work, we have leveraged our knowledge on ionic strength effects on the reactive uptakes of gas-phase ozone on aqueous pyruvic acid (PA) or humic acid (HA) by the vertical wetted wall flow tube technique. A relatively weak dependence was observed between the uptake coefficients of O3 and the concentration of Br- in the absence of organics. The uptake coefficients of ozone increased markedly at elevated bromide concentrations in presence of pyruvic acid or humic acid. This finding clearly indicates that the dry deposition of ozone to the sea surface could be significantly enhanced by carbonyl compounds (e.g., pyruvic acid) or humic acid that occur at the bromide-rich sea surface microlayer. Based on the observed uptake coefficients, the estimated deposition velocity of ozone for nM-range PA concentrations is 9.7 x 10-4 m s-1, in the same order as the upper-limit ozone deposition velocity due to the ozone reaction with chlorophyll (1 x 10-5 m s-1 to 1 x 10-3 m s-1), and higher than the deposition velocity of 1.2 x 10-4 m s-1 assessed for the reaction of ozone with a mixture of DOM and iodide (Mekic et al., 2018). Therefore, the surface reaction between ozone and PA makes an important contribution to the ozone deposition velocity on the ocean surface. We also evaluated the formation of oligomeric species during the heterogeneous reaction of ozone with pyruvic acid or humic acid in dilute aqueous phase by the means of Ultrahigh-Resolution Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. A comparison between the previous results and the present ones suggests that the products formed from the reaction of O3 with organic compounds at the water surface (at low ionic strength, which under environmental conditions could be the surface of cloud droplets and aerosol deliquescent particles), either in the dark or under irradiation exhibit much more complex structure than the products formed upon photolytic degradation of pyruvic acid or humic acid in the bulk aqueous phase.

Ionic strength effects on the reactive uptake of ozone on organic compounds: Implications for air-sea ozone deposition

2019 Fall National Meeting

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