Pan-Arctic surface ozone: modelling vs. measurements
Authors: Yang Xin , Blechschmidt Anne-M. , Bognar Kristof , McClure-Begley Audra , Morris Sara , Petropavlovskikh Irina , Richter Andreas , Skov Henrik , Strong Kimberly , Tarasick David W. , Uttal Taneil , Vestenius Mika , Zhao Xiaoyi 
Published: December 2020

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.