I'm back
Well, the one advantage San Francisco has is the odd confluence of currents
just off the coast about 5 miles out from the mouth of the bay that causes the
fog to roll in and the old inland air to be flushed.
The problem with coal is twofold; first, it tended to be burned
inefficiently in iron stoves within rooms which allowed the particulates to
circulate indoors where they were pretty well trapped through the winters. Coal
furnaces spewed it into the air; that was the source of London's killer fogs.
Coal has an additional problem in that it is a perfect container for radon
gas, which is released where it is burned or crushed and which most in
government rank as equal to smoking in lung cancer cause (many places in the
U.S. where there are major coal deposits underground have radon building up in
their basements from the weight of the house on the bedrock!).
The point is, it just isn't all that simple.