The Great Smog of London
From 5th December 1952 until 9th December, a thick layer of smog covered the city. A "pea souper".
At least 4000 people died as a result; another 6-8 thousand died later as a direct result. 100,000 were made ill by the effects of the smog on the respiration system.
The cause of the smog was the burning of poor quality coal (which is cheaper), plus a temperature inversion trapping cold air in London, and there wasn't much wind.
Visibility was down to a few meters; driving became impossible. Public transport stopped. Ambulances couldn't function.
The reaction to the smog was the Clean Air acts. People were encouraged to burn "smokeless" fuel; coke or gas. But that didn't solve the problem, because coke and gas were produced by burning coal. It simply moved the problem from the location of consumption, to the location of the production of these fuels.
And then it all happened again in December 1962, killing 750 people.
But these days, although we often see mist (which is just water droplets in the air), we don't see smog, or even fog.
This is because of the Clean Air acts. These were the first examples of environmental legislation; a recognition that people should not be free to do things that are likely to harm other people, even when that harm isn't immediate and obvious.
I remember that in our house, we burned "smokeless" coal and paraffin to keep warm.
Then there were the Clean Air acts of 1968 and 1993.
Now that most domestic heating is with North Sea gas (methane) and electricity (which today uses very little coal), the problem of pollution from domestic heating is much diminished.