Pan-Arctic surface ozone: modelling vs measurements

Abstract

<p><strong>Abstract.</strong> Within the framework of the International Arctic Systems for Observing the Atmosphere (IASOA), we report a modelling-based study on surface ozone across the Arctic. We use surface ozone from six sites: Summit (Greenland), Pallas (Finland), Barrow (USA), Alert (Canada), Tiksi (Russia), and Villum Research Station (VRS) at Station Nord (North Greenland, Danish Realm), and ozonesonde data from three Canadian sites: Resolute, Eureka, and Alert. Two global chemistry models: a global chemistry transport model (p-TOMCAT) and a global chemistry climate model (UKCA), are used for model-data comparisons. Remotely sensed data of BrO from the GOME-2 satellite instrument and ground-based Multi-axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at Eureka, Canada are used for model validation.</p><p> The observed climatology data show that spring surface ozone at coastal sites is heavily depleted, making ozone seasonality at Arctic coastal sites distinctly different from that at inland sites. Model simulations show that surface ozone can be greatly reduced by bromine chemistry. In April, bromine chemistry can cause a net ozone loss (monthly mean) of 10–20 ppbv, with almost half attributable to open-ocean-sourced bromine and the rest to sea-ice-sourced bromine. However, the open-ocean-sourced bromine, via sea spray bromide depletion, cannot by itself produce ozone depletion events (ODEs) (defined as ozone volume mixing ratios VMRs < 10 ppbv). In contrast, sea-ice-sourced bromine, via sea salt aerosol (SSA) production from blowing snow, can produce ODEs even without bromine from sea spray, highlighting the importance of sea ice surface in polar boundary layer chemistry.</p><p> Model bromine is sensitive to model configuration, e.g., under the same bromine loading, the total inorganic bromine (BrY) in the Arctic spring boundary layer in the p-TOMCAT base run (i.e., with all bromine emissions) can be 2 times larger than that in the UKCA base run. Despite the model differences, both model base runs can successfully reproduce large bromine explosion events (BEEs) in polar spring. Model-integrated tropospheric column BrO generally matches GOME-2 tropospheric columns within ~50 % (in the UKCA base run) and factors of 2–3 (in the p-TOMCAT base run). The success of the models in reproducing both ODEs and BEEs in the Arctic indicates that the relevant parameterizations implemented in the models work reasonably well, which supports the proposed mechanism of SSA and bromine production from blowing snow on sea ice. Given that sea ice is a large source of SSA and halogens, changes in sea ice type and extent in a warming climate will influence Arctic boundary layer chemistry, including the oxidation of atmospheric elemental mercury.</p>

Variability in gaseous elemental mercury at Villum Research Station, Station Nord, in North Greenland from 1999 to 2017

“…GEM was averaged to a time resolution of 0.5 h. The new analysis confirmed the previous result, though the data points were more scattered, and thus, the resulting slope had a higher uncertainty, mostly due to smaller difference between the initial GEM concentration and the final concentration. An important point regarding the parameterisation of GEM depletion is that bromine-induced atmospheric mercury depletion events (AMDEs) were often observed under stagnant wind conditions and not only during situations with strong wind that may cause bromine release as proposed earlier (see Yang et al, 2020). Recently, the bromine-induced oxidation of Hg 0 has been proven directly in a study, where Br, BrO, O 3 , GEM and gaseous oxidised mercury (GOM) were measured simultaneously during AMDE and ODE, using a multiphase box model to study the complex set of processes (Wang et al, 2019).…”

“…Today, China accounts for about 40 % of the global Hg emissions (Muntean et al, 2014;Streets et al, 2019Streets et al, , 2017Streets et al, , 2018. In North America, Europe and on the North Atlantic, there is a decline in the GEM concentration of between −1.5 % yr −1 and −2.2 % yr −1 (Zhang et al, 2016). In the Arctic, the decline is zero at Svalbard and −0.9 % at Alert (Cole et al, 2013).…”

Long-term time series of Arctic tropospheric BrO derived from UV–VIS satellite remote sensing and its relation to first-year sea ice

“…There are also several studies which tried to model tropospheric BrO plumes. Yang et al (2020) used both a chemistry transport and a chemistry climate model to model tropospheric BrO and compared the outputs with satellite columns and ground-based measurements. Fernandez et al (2019) provided 4 years of polar spring comparisons between GOME-2A instrument columns and model runs, for the Arctic and Antarctic, having implemented polar halogen chemistry into the CAM-Chem model.…”

Implementation and Impacts of Surface and Blowing Snow Sources of Arctic Bromine Activation Within WRF‐Chem 4.1.1

“…Model studies on polar aerosols also demonstrate an improved agreement compared to sea salt observations for winter and spring when blowing snow sourced sea salt aerosols are included (Rhodes et al, 2017;Huang et al, 2018). Further, this has been recently shown to improve model predictions of BrO and O 3 (Huang et al, 2020;Yang et al, 2020). Finally, observations show that aerosols can sustain bromine activation above the boundary layer (Peterson et al, 2017), but it has not yet been clearly demonstrated from measurements that blowing snow sourced sea salt aerosols trigger bromine explosion events.…”