[jellicle]

Toronto, Ontario is 400km from Ohio, and gets smog from Ohio's coal plants all the time. The studies suggest about half of Toronto's air pollution is due to U.S. power plants.

I have no idea what the reality is of smog in Europe, but your off-hand dismissal of this based on the perceived distance between the source and recipient of the pollution is entirely wrong.

[ptaipale]

However, the prevailing wind in Europe is from southwest. Paris doesn't get smog from the Ruhr, mostly it is vice versa.

Of course, occasionally the wind is the other way round, but overall, any bad air in Paris is due to Paris.