There is a 20 questions Q & A paper attached to the WMO “Scientific Assessment of Ozone Depletion: 2006″.
In the second column in Question 2 – near top right page Q4 – is the statement:
“Some stratospheric ozone is transported down into the troposphere and can influence ozone amounts at Earth’s surface, particularly in remote, unpolluted regions of the globe.“
Natural processes that can cause injection of stratospheric ozone down into the surface layer will happen regardless of whether the location is above “…remote, unpolluted regions of the globe.” or above urban and inhabited areas.
I think the WMO should rewrite the above very odd passage – without any spin.
There is a controversy about the origin of common high levels (circa 50-100ppb) in peak daily surface level ozone measured at non-urban stations.
The WMO view would emphasise that these are due to mass transport of polluted urban air – outward to rural sites.
The opposing view that I see evidence for in my studies of hourly air monitoring data – is that daily ozone peaks can form in rural air due to natural ozone precurssor chemical species.