Abstract
Abstract. 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 ozone-sonde data from three Canadian sites: Resolute, Eureka, and Alert. Two global chemistry models – a global chemistry transport model (parallelised-Tropospheric Offline Model of Chemistry and Transport, p-TOMCAT) and a global chemistry climate model (United Kingdom Chemistry and Aerosol, 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. 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. Modelled total inorganic bromine (BrY) over the Arctic sea ice is sensitive to model configuration; e.g. under the same bromine loading, BrY in the Arctic spring boundary layer in the p-TOMCAT control run (i.e. with all bromine emissions) can be 2 times that in the UKCA control run. Despite the model differences, both model control runs can successfully reproduce large bromine explosion events (BEEs) and ODEs in polar spring. Model-integrated tropospheric-column BrO generally matches GOME-2 tropospheric columns within ∼ 50 % in UKCA and a factor of 2 in p-TOMCAT. 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 production and bromide release 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. Note that this work dose not necessary rule out other possibilities that may act as a source of reactive bromine from the sea ice zone.
Highlights
Climatological data show that mean surface ozone across the Arctic is ∼ 5 ppbv higher than that in the Antarctic (Helmig et al, 2007a), reflecting the impact of anthropogenic emissions of ozone precursors such as NOx (= NO + NO2) and volatile organic compounds (VOCs) in the Northern Hemisphere (NH; e.g. Law and Stohl, 2007; Quinn et al, 2008; Walker et al, 2012; Ancellet et al, 2016)
Global Ozone Monitoring Experiment-2 (GOME-2) tropospheric bromine monoxide (BrO) column maps (0.5 × 0.5◦ grid) and time series based on subsetted data of VCDtrop at the Resolute, Eureka, and Alert sites are used here
The summer minimum is thought to be attributable to enhanced ozone photo-dissociation, where NOx levels are low, and increased dry deposition to plants (e.g. Hatakka et al, 2003; Engvall Stjernberg et al, 2011)
Summary
Climatological data show that mean surface ozone across the Arctic is ∼ 5 ppbv higher than that in the Antarctic (Helmig et al, 2007a), reflecting the impact of anthropogenic emissions of ozone precursors such as NOx (= NO + NO2) and volatile organic compounds (VOCs) in the Northern Hemisphere (NH; e.g. Law and Stohl, 2007; Quinn et al, 2008; Walker et al, 2012; Ancellet et al, 2016). Analyses of Arctic transport (Bottenheim and Chan 2006; Liu et al, 2013) as well as in situ measurements (Bottenheim et al, 2009; Jacobi et al, 2010; Seabrook et al, 2013) suggest that the near-surface ozone minimum in spring is not limited to coastal sites but covers much of the Arctic basin, indicating that the sources of bromine are mainly sea-ice-related (e.g. Simpson et al, 2007a; Abbatt et al, 2012). Global chemical models have been used to test chemical schemes for interpreting or reproducing observed spring ODEs and BEEs. For instance, Toyota et al (2011) and Falk and Sinnhuber (2018) focused on snowpack-released bromine, while Yang et al (2010) and Choi et al (2012, 2018) considered blowing-snow-sourced bromine.
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