Trends in tropospheric ozone, an important air pollutant and
short-lived climate forcer (SLCF), are estimated using available surface
and ozonesonde profile data for 1993-2019. Using a coherent methodology,
observed trends are compared to modeled trends (1995-2015) from the
Arctic Monitoring Assessment Programme SLCF 2021 assessment.
Statistically significant increases in observed surface ozone at Arctic
coastal sites, notably during winter, and concurrent decreasing trends
in surface carbon monoxide, are generally captured by multi-model median
(MMM) trends. Wintertime increases are also estimated in the free
troposphere at most Arctic sites, but tend to be overestimated by the
MMMs. Springtime surface ozone increases in northern coastal Alaska are
not simulated while negative springtime trends in northern Scandinavia
are not always reproduced. Possible reasons for observed changes and
model behavior are discussed, including decreasing precursor emissions,
changing ozone sinks, and variability in large-scale meteorology.