Role of oceanic ozone deposition in explaining temporal variability in surface ozone at High Arctic sites
<p>Dry deposition is an important removal mechanism for tropospheric ozone (O<span class="inline-formula"><sub>3</sub></span>). Currently, O<span class="inline-formula"><sub>3</sub></span> deposition to oceans in atmospheric c...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2021-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/10229/2021/acp-21-10229-2021.pdf |
| Summary: | <p>Dry deposition is an important removal mechanism for tropospheric ozone (O<span class="inline-formula"><sub>3</sub></span>). Currently, O<span class="inline-formula"><sub>3</sub></span> deposition to oceans in atmospheric chemistry and transport models (ACTMs) is generally represented using constant surface uptake resistances. This occurs despite the role of solubility, waterside turbulence and O<span class="inline-formula"><sub>3</sub></span> reacting with ocean water reactants such as iodide resulting in substantial spatiotemporal variability in O<span class="inline-formula"><sub>3</sub></span> deposition and concentrations in marine boundary layers. We hypothesize that O<span class="inline-formula"><sub>3</sub></span> deposition to the Arctic Ocean, having a relatively low reactivity, is overestimated in current models with consequences for the tropospheric concentrations, lifetime and long-range transport of O<span class="inline-formula"><sub>3</sub></span>. We investigate the impact of the representation of oceanic O<span class="inline-formula"><sub>3</sub></span> deposition to the simulated magnitude and spatiotemporal variability in Arctic surface O<span class="inline-formula"><sub>3</sub></span>.</p>
<p>We have integrated the Coupled Ocean-Atmosphere Response Experiment Gas transfer algorithm (COAREG) into the mesoscale meteorology and atmospheric chemistry model Polar-WRF-Chem (WRF) which introduces a dependence of O<span class="inline-formula"><sub>3</sub></span> deposition on physical and biogeochemical drivers of oceanic O<span class="inline-formula"><sub>3</sub></span> deposition. Also, we reduced the O<span class="inline-formula"><sub>3</sub></span> deposition to sea ice and snow. Here, we evaluate WRF and CAMS reanalysis data against hourly averaged surface O<span class="inline-formula"><sub>3</sub></span> observations at 25 sites (latitudes <span class="inline-formula">></span> 60<span class="inline-formula"><sup>∘</sup></span> N). This is the first time such a coupled modeling system has been evaluated against hourly observations at pan-Arctic sites to study the sensitivity of the magnitude and temporal variability in Arctic surface O<span class="inline-formula"><sub>3</sub></span> on the deposition scheme. We find that it is important to nudge WRF to the ECMWF ERA5 reanalysis data to ensure adequate meteorological conditions to evaluate surface O<span class="inline-formula"><sub>3</sub></span>.</p>
<p>We show that the mechanistic representation of O<span class="inline-formula"><sub>3</sub></span> deposition over oceans and reduced snow/ice deposition improves simulated Arctic O<span class="inline-formula"><sub>3</sub></span> mixing ratios both in magnitude and temporal variability compared to the constant resistance approach. Using COAREG, O<span class="inline-formula"><sub>3</sub></span> deposition velocities are in the order of 0.01 cm s<span class="inline-formula"><sup>−1</sup></span> compared to <span class="inline-formula">∼</span> 0.05 cm s<span class="inline-formula"><sup>−1</sup></span> in the constant resistance approach. The simulated monthly mean spatial variability in the mechanistic approach (0.01 to 0.018 cm s<span class="inline-formula"><sup>−1</sup></span>) expresses the sensitivity to chemical enhancement with dissolved iodide, whereas the temporal variability (up to <span class="inline-formula">±</span>20 % around the mean) expresses mainly differences in waterside turbulent transport. The mean bias for six sites above 70<span class="inline-formula"><sup>∘</sup></span> N reduced from <span class="inline-formula">−</span>3.8 to 0.3 ppb with the revision to ocean and snow/ice deposition. Our study confirms that O<span class="inline-formula"><sub>3</sub></span> deposition to high-latitude oceans and snow/ice is generally overestimated in ACTMs. We recommend that a mechanistic representation of oceanic O<span class="inline-formula"><sub>3</sub></span> deposition is preferred in ACTMs to improve the modeled Arctic surface O<span class="inline-formula"><sub>3</sub></span> concentrations in terms of magnitude and temporal variability.</p> |
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| ISSN: | 1680-7316 1680-7324 |