  Ozone ($\textrm{O}_3$) is important for the survival of life on Earth because
it shields the surface from ionising ultraviolet (UV) radiation. However, the
existence of $\textrm{O}_3$ in Earth's atmosphere is not always beneficial.
Resulting from anthropogenic activity, $\textrm{O}_3$ exists as a biologically
harmful pollutant at the surface when it forms in the presence of sunlight and
other pollutants. As a strong oxidiser, $\textrm{O}_3$ can be lethal to several
different organisms; thus, when assessing the potential habitability of an
exoplanet, a key part is determining whether toxic gases could be present at
its surface. Using the Whole Atmosphere Community Climate Model version 6
(WACCM6; a three-dimensional chemistry-climate model), twelve atmospheric
simulations of the terrestrial exoplanet TRAPPIST-1 e are performed with a
variety of $\textrm{O}_2$ concentrations and assuming two different stellar
spectra proposed in the literature. Four atmospheric simulations of the
exoplanet Proxima Centauri b are also included. Some scenarios for both
exoplanets exhibit time-averaged surface $\textrm{O}_3$ mixing ratios exceeding
harmful levels of 40 ppbv, with 2200 ppbv the maximum concentration found in
the cases simulated. These concentrations are toxic and can be fatal to most
life on Earth. In other scenarios $\textrm{O}_3$ remains under harmful limits
over a significant fraction of the surface, despite there being present regions
which may prove inhospitable. In the case that $\textrm{O}_3$ is detected in a
terrestrial exoplanet's atmosphere, determining the surface concentration is an
important step when evaluating a planet's habitability.
