Abstract
The daily variation of ground-level ozone (O3), a
harmful pollutant, is positively correlated with air temperature (T) in
many midlatitude land regions in the summer. The observed temporal
regression slope between O3 and T is referred to as the
“ozone-climate change penalty” and has been proposed as a way to
predict the impact of future climate warming on O3 from
observations. Here, we use two chemical transport models to show that
the O3-T correlation is primarily due to the meridional
advection of both fields, as opposed to direct temperature-dependent
chemistry or emissions. Furthermore, the magnitude of the
O3-T regression (dO3/dT) can be
estimated by the ratio of the time-mean O3 and T
meridional gradients. Consideration of expected changes in the
meridional gradients of T and O3 due to climate change
indicates that dO3/dT will likely change, and caution is
needed when using the observed climate penalty to predict
O3 changes.