Trying to find sci fi book, circa 1965, global crisis, raining soot, underground community, portal to surface?

Question

trying to find a sci fi book about 40 yrs old, in which there was some global ecological crisis causing survivors to move underground, raining soot on the earths surface. Sound familiar to anyone?

Answer 1

Yes, I read that book but honestly I cannot remember the title to it. It may have been a short story but I'm not sure.