Arctic tropospheric ozone: assessment of current knowledge and model performance
Authors: Whaley Cynthia H. , Law Kathy S. , Hjorth Jens Liengaard , Skov Henrik , Arnold Stephen R. , Langner Joakim , Pernov Jakob Boyd , Bergeron Garance , Bourgeois Ilann , Christensen Jesper H. , Chien Rong-You , Deushi Makoto , Dong Xinyi , Effertz Peter , Faluvegi Gregory , Flanner Mark , Fu Joshua S. , Gauss Michael , Huey Greg , Im Ulas , Kivi Rigel , Marelle Louis , Onishi Tatsuo , Oshima Naga , Petropavlovskikh Irina , Peischl Jeff , Plummer David A. , Pozzoli Luca , Raut Jean-Christophe , Ryerson Tom , Skeie Ragnhild , Solberg Sverre , Thomas Manu A. , Thompson Chelsea , Tsigaridis Kostas , Tsyro Svetlana , Turnock Steven T. , von Salzen Knut , Tarasick David W. 
Published: January 2023

Abstract. As the third most important greenhouse gas (GHG) after carbon
dioxide (CO2) and methane (CH4), tropospheric ozone (O3) is also
an air pollutant causing damage to human health and ecosystems. This study
brings together recent research on observations and modeling of tropospheric
O3 in the Arctic, a rapidly warming and sensitive environment. At
different locations in the Arctic, the observed surface O3 seasonal
cycles are quite different. Coastal Arctic locations, for example, have a
minimum in the springtime due to O3 depletion events resulting from
surface bromine chemistry. In contrast, other Arctic locations have a
maximum in the spring. The 12 state-of-the-art models used in this study
lack the surface halogen chemistry needed to simulate coastal Arctic surface
O3 depletion in the springtime; however, the multi-model median (MMM)
has accurate seasonal cycles at non-coastal Arctic locations. There is a
large amount of variability among models, which has been previously reported, and we show that there continues to be no convergence among
models or improved accuracy in simulating tropospheric O3 and its
precursor species. The MMM underestimates Arctic surface O3 by 5 % to
15 % depending on the location. The vertical distribution of tropospheric
O3 is studied from recent ozonesonde measurements and the models. The
models are highly variable, simulating free-tropospheric O3 within a
range of ±50 % depending on the model and the altitude. The MMM
performs best, within ±8 % for most locations and seasons. However,
nearly all models overestimate O3 near the tropopause (∼300 hPa or ∼8 km), likely due to ongoing issues with
underestimating the altitude of the tropopause and excessive downward
transport of stratospheric O3 at high latitudes. For example, the MMM
is biased high by about 20 % at Eureka. Observed and simulated O3
precursors (CO, NOx, and reservoir PAN) are evaluated throughout the
troposphere. Models underestimate wintertime CO everywhere, likely due to a
combination of underestimating CO emissions and possibly overestimating OH.
Throughout the vertical profile (compared to aircraft measurements), the MMM
underestimates both CO and NOx but overestimates PAN. Perhaps as a
result of competing deficiencies, the MMM O3 matches the observed
O3 reasonably well. Our findings suggest that despite model updates
over the last decade, model results are as highly variable as ever and have
not increased in accuracy for representing Arctic tropospheric O3.