Coastal Measurements of Ozone Deposition to the Sea by Eddy Covariance

Dry deposition of ozone is an important part of the global tropospheric ozone budget, approximately a third of which occurs over the oceans. However, direct measurements of this deposition are sparse, and our understanding of the processes which control it incomplete. The few observational studies that do exist report notably disparate values, leading to great uncertainty in model estimates of the tropospheric ozone burden and deposition rates. This uncertainty is compounded by the unquantified effects of organic molecules in the sea-surface microlayer.

Here we report recent ozone flux measurements made using the eddy covariance method at the Penlee Point Atmospheric Observatory on the south coast of the UK. The measurements were conducted from 10^th April to 21^st May 2018, while biological activity was growing in the coastal water as the spring bloom was approaching. Ozone was detected using a high frequency instrument based on the chemiluminescent reaction of O₃ with NO. Samples of the sea-surface microlayer were also collected within the flux footprint for ongoing analyses including total/dissolved organic carbon, iodide concentration, surfactant concentration and surface tension.

Deposition velocities of 0.017 - 0.065 cm s^-1 (25^th - 75^th percentile) were observed from 10^th April to 21^st May 2018, and increased with friction velocity at moderate-high wind speeds. These deposition velocities are slightly higher than reported for the open ocean, but similar to values recorded for coastal regions. In this presentation we will discuss ongoing coastal ozone flux measurements, as well as the influence of sea surface composition, wind, and tide on the ozone deposition velocity.