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

Barten, Johannes G. M.; Ganzeveld, Laurens N.; Steeneveld, Gert-Jan; Krol, Maarten C.

Dry deposition is an important removal mechanism for tropospheric ozone (Oinline-formula3). Currently, Oinline-formula3 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 Oinline-formula3 reacting with ocean water reactants such as iodide resulting in substantial spatiotemporal variability in Oinline-formula3 deposition and concentrations in marine boundary layers. We hypothesize that Oinline-formula3 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 Oinline-formula3. We investigate the impact of the representation of oceanic Oinline-formula3 deposition to the simulated magnitude and spatiotemporal variability in Arctic surface Oinline-formula3.

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 Oinline-formula3 deposition on physical and biogeochemical drivers of oceanic Oinline-formula3 deposition. Also, we reduced the Oinline-formula3 deposition to sea ice and snow. Here, we evaluate WRF and CAMS reanalysis data against hourly averaged surface Oinline-formula3 observations at 25 sites (latitudes inline-formula> 60inline-formula 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 Oinline-formula3 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 Oinline-formula3.

We show that the mechanistic representation of Oinline-formula3 deposition over oceans and reduced snow/ice deposition improves simulated Arctic Oinline-formula3 mixing ratios both in magnitude and temporal variability compared to the constant resistance approach. Using COAREG, Oinline-formula3 deposition velocities are in the order of 0.01 cm sinline-formula−1 compared to inline-formula∼ 0.05 cm sinline-formula−1 in the constant resistance approach. The simulated monthly mean spatial variability in the mechanistic approach (0.01 to 0.018 cm sinline-formula−1) expresses the sensitivity to chemical enhancement with dissolved iodide, whereas the temporal variability (up to inline-formula±20 % around the mean) expresses mainly differences in waterside turbulent transport. The mean bias for six sites above 70inline-formula N reduced from inline-formula−3.8 to 0.3 ppb with the revision to ocean and snow/ice deposition. Our study confirms that Oinline-formula3 deposition to high-latitude oceans and snow/ice is generally overestimated in ACTMs. We recommend that a mechanistic representation of oceanic Oinline-formula3 deposition is preferred in ACTMs to improve the modeled Arctic surface Oinline-formula3 concentrations in terms of magnitude and temporal variability.

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Barten, Johannes G. M. / Ganzeveld, Laurens N. / Steeneveld, Gert-Jan / et al: Role of oceanic ozone deposition in explaining temporal variability in surface ozone at High Arctic sites. 2021. Copernicus Publications.

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