I remember when this kind of milky polluted air was the norm for any prolonged period of high pressure. Only really in the late 80s and 1990s did things improve, as sulphurous fuels were phased out, scrubbers added to factories and vehicle emissions properly controlled. It's a tribute in some ways to how much we have improved things in Western Euriope that events like this weeks' are remarked upon.
At the same time rivers and lakes across the continent that used to be virtually lifeless toxic sumps have been cleaned, seen the fish and the swimmers return. In my view the cleaning up of the post-industrial environment in the last 3 decades is one of the greatest achievements of modern Europe and (in places) North America. The Chinese and Indians are seeing at first hand what this continent used to look and smell like not so long ago.
I suspect the main culprit for this spell of pollution is the good old motor car, maybe with a few coal fired power stations thrown in.
Brockley, South East London 30m asl