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.
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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.
I’ve done no specific observation, but I seem to recall from my chemistry days that (a) ozone is produced from electric arcs, such as from the brushes of electric motors and generators that have them, welders, etc and (b) it can be produced in moderate amounts by lightning. It would surprise me greatly if there was not an appreciable level of permanent ozone that did not come from high altitudes. Maybe it is time to do an audit on the whole ozone cycle – I have been suspicious of several core assumptions for decades now, but have not dissected them.
There’s also low level ozone produced by photochemical reactions with Volatile Organic Compounds (VOCs).
Different VOCs have different POCP – photochemical ozone creation potentials. The resultant mix is a factor in smog.
As well as VOCs from painting, solvent use etc in industrial and domestic processes there’re also natural VOC emissions from trees.
That is right RobinG.
Did you see this ref off my Perth ozone page where airborne salt is also fingered as a cause of tropospheric ozone.