Atmospheric chemistry at the ocean surface: investigating ozonolysis in the sea surface microlayer

Reactive dry deposition in the marine environment is a significant sink of surface level ozone in the troposphere. Previous measurements are sparse but indicate that the uncertainties in quantifying this loss are high. This thesis presents additional measurements of ozone deposition to both synthetic and real seawater samples to attempt to reduce these uncertainties. A new flow reactor was used to measure the second order rate constant for the reaction of ozone and dissolved iodide, matching the number of measurements of this value at room temperature in the literature. A value of 1.94 +/- 0.20 x10^9 M^-1 s^-1 was obtained, reducing the error in this measurement from 28% to 10%. Ozone deposition was measured onto synthetic seawater samples containing unsaturated fatty acids. The reaction proceeded according to the Langmuir-Hinshelwood surface reaction mechanism, as expected for the reaction of ozone and organics. It was shown that reactivity increased with increasing number of double bonds and in the presence of dissolved iodide. It was also shown that organic molecules partially inhibit the reaction of ozone with dissolved iodide. Surface and underlying water samples were collected from the North Sea in 2017 and 2018 and the ozone depositions measured. A deposition of ozone was estimated based on measured iodide concentration measurements and the rate constant mentioned previously. These were compared to actual measured ozone deposition; iodide was found to contribute between 8% and 43% of the measured reactive ozone loss, considerably less than estimated previously.