noun
soot
Black powdery substance from smoke, often found in chimneys or on surfaces after a fire.
暖炉のすすを掃除する。
I clean the soot from the fireplace.
天井にすすがついている。
There is soot on the ceiling.
煙 is smoke in general, while すす is the black soot residue left by smoke.
The origin is uncertain; the kanji 煤 is conventionally associated with soot.