Role of oceanic ozone deposition in explaining temporal variability in surface ozone at High Arctic sites.

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From: Atmospheric Chemistry and Physics(Vol. 21, Issue 13)
Publisher: Copernicus GmbH
Document Type: Article
Length: 461 words

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Abstract :

Dry deposition is an important removal mechanism for tropospheric ozone (O.sub.3). Currently, O.sub.3 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.sub.3 reacting with ocean water reactants such as iodide resulting in substantial spatiotemporal variability in O.sub.3 deposition and concentrations in marine boundary layers. We hypothesize that O.sub.3 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.sub.3 . We investigate the impact of the representation of oceanic O.sub.3 deposition to the simulated magnitude and spatiotemporal variability in Arctic surface O.sub.3. 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.sub.3 deposition on physical and biogeochemical drivers of oceanic O.sub.3 deposition. Also, we reduced the O.sub.3 deposition to sea ice and snow. Here, we evaluate WRF and CAMS reanalysis data against hourly averaged surface O.sub.3 observations at 25 sites (latitudes 60.sup." 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.sub.3 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.sub.3. We show that the mechanistic representation of O.sub.3 deposition over oceans and reduced snow/ice deposition improves simulated Arctic O.sub.3 mixing ratios both in magnitude and temporal variability compared to the constant resistance approach. Using COAREG, O.sub.3 deposition velocities are in the order of 0.01 cm s.sup.-1 compared to ⼠0.05 cm s.sup.-1 in the constant resistance approach. The simulated monthly mean spatial variability in the mechanistic approach (0.01 to 0.018 cm s.sup.-1) expresses the sensitivity to chemical enhancement with dissolved iodide, whereas the temporal variability (up to ±20 % around the mean) expresses mainly differences in waterside turbulent transport. The mean bias for six sites above 70.sup." N reduced from -3.8 to 0.3 ppb with the revision to ocean and snow/ice deposition. Our study confirms that O.sub.3 deposition to high-latitude oceans and snow/ice is generally overestimated in ACTMs. We recommend that a mechanistic representation of oceanic O.sub.3 deposition is preferred in ACTMs to improve the modeled Arctic surface O.sub.3 concentrations in terms of magnitude and temporal variability.

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Gale Document Number: GALE|A667733495