Often in winter Milan is covered in fog when the rest
of the area isn't.
Hmm ... your experience is possibly a bit dated.
by 15 to 20 years. From the air, I could often see fog over
Milan when the rest of the area was clear. Fog not smog.

Is fog globally endangered? When I first arrived in Edinburgh
in the 1970s, you would usually get a thick fog ("haar") over
the city in the morning in late summer, drifting in from the
North Sea. It was quite lovely; from the hills in the south
you could look down to see Edinburgh slowly emerging from it as
the sun came up, church spires first. The old stone tenements
in the New Town looked their most atmospheric at that time.
But you see it much less often now.

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