Mechanistic Ocean-Atmosphere exchange of trace gases in Polar-WRF-Chem: Implications for Arctic tropospheric ozone

Sjoerd Barten,Gert-Jan Steeneveld,Laurens Ganzeveld,Maarten Krol

doi:10.5194/ems2022-144

Abstract

&lt;p&gt;Dry deposition is an important removal mechanism for tropospheric ozone (O&lt;sub&gt;3&lt;/sub&gt;). Its deposition to oceans is generally represented in atmospheric chemistry transport models using constant surface uptake resistances. However, observations show quite large spatiotemporal variability expressing differences in solubility, waterside turbulence and O&lt;sub&gt;3&lt;/sub&gt; reacting with iodide and dissolved organic matter. We hypothesize that for the Arctic O&lt;sub&gt;3&lt;/sub&gt; deposition is overestimated with consequences for background concentrations and lifetime of O&lt;sub&gt;3&lt;/sub&gt; also due to changes in long-range transport of O&lt;sub&gt;3&lt;/sub&gt; and its precursors. These are focal points of a project on observing and modelling of Arctic climate-active trace gas exchange as a contribution to the MOSAiC observational campaign with the icebreaker Polarstern being trapped in the Arctic sea-ice for ~1 year.&lt;/p&gt;&lt;p&gt;We have coupled the Coupled Ocean-Atmosphere Response Experiment Gas transfer algorithm (COAREG) to the mesoscale meteorology and atmospheric chemistry model Polar-WRF-Chem (PWRF-C). This includes a further development including a two-layer scheme for O&lt;sub&gt;3&lt;/sub&gt; deposition to oceans and coupling to recently updated ocean water composition databases. We have also reduced the deposition of O&lt;sub&gt;3&lt;/sub&gt; to sea ice based on a previous study of snow-ice O&lt;sub&gt;3&lt;/sub&gt; deposition.&lt;/p&gt;&lt;p&gt;In this study, we evaluate the performance of PWRF-C with hourly-averaged surface O&lt;sub&gt;3&lt;/sub&gt; measurements above 60 &amp;#186;N and with O&lt;sub&gt;3&lt;/sub&gt; sondes. We show that the more mechanistic representation of O&lt;sub&gt;3&lt;/sub&gt; deposition over oceans and strongly reduced deposition over snow and ice results in improved simulated Arctic O&lt;sub&gt;3 &lt;/sub&gt;mixing ratios. We found that it is important to nudge PWRF-C to the ECMWF ERA-Interim wind fields which secures a fair comparison of the model with measurements regarding their footprint. Our study indicates that representation of ocean and sea-ice O&lt;sub&gt;3&lt;/sub&gt; deposition in atmospheric chemistry models must be revised to improve the representation of Arctic O&lt;sub&gt;3&lt;/sub&gt; concentrations and chemistry.&lt;/p&gt;

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