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%In the troposphere ozone is a trace gas mostly generated by photochemistry, due to both pollution and natural processes.   %Stratosphere to Troposphere Transport of ozone events(STTs) are a relatively small source of tropospheric ozone, however the regional %effect can be quite large and the dynamics which cause these events are not perfectly understood \cite{Mihalikova2012,Zhang_2014}.  Ozone is present in the troposphere due to a variety of dynamical and photochemical processes, including irreversible transport down from the ozone-rich stratosphere and anthropogenic pollution. Ozone-rich air mixes irreversibly down from the stratosphere during meteorologically conducive conditions \citep{Sprenger2003,Milhalikova2012}; these are referred to as Statosphere - Troposphere Transport (STT) events. In the extra-tropics, STT most commonly occurs during tropopause folds \citep{Sprenger2003. \citep{Sprenger2003}.  These synoptic-scale folds are characterised by tongues of high PV air descending to low altitudes. These tongues may become elongated and filaments separate from the tongue which mix into tropospheric air. Stratospheric ozone brought deeper (lower) into the troposphere are more likely to affect the surface ozone budget and tropospheric chemistry \citep{Zanis2003} \citep{Zanis2003}.  While the amount of tropospheric ozone is small compared with that found in the stratosphere, it is an important constituent \textbf{XXXX - Robyn you might like to add some chemistry stuff here...}. The relative contributions to the tropospheric ozone budget of photochemistry and STT (dynamical transport) is still uncertain \citet{Zanis2003}.