Pan-Arctic surface ozone: modelling vs measurements

• Main Authors: Yang, Xin, Blechschmidt, Anne-M, Bognar, Kristof, McClure–Begley, Audra, Morris, Sara, Petropavlovskikh, Irina, Richter, Andreas, Skov, Henrik, Strong, Kimberly, Tarasick, David, Uttal, Taneil, Vestenius, Mika, Zhao, Xiaoyi
• Format: Text
• Language: English
• Published: 2020
• Subjects: Arctic; Canada; Eureka; Greenland; Station Nord; Tiksi; North Greenland; Sea ice
• Online Access: https://doi.org/10.5194/acp-2019-984; https://www.atmos-chem-phys-discuss.net/acp-2019-984/

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. 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. 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.