From the article it seems it was assumed to just be soot for a long time which was considered normal in many places until we got more serious about pollution.

From the article it seems it was assumed to just be soot for a long time which was considered normal in many places until we got more serious about pollution. Check out the before and afters with soot here it's very similar https://www.manchestereveningnews.co.uk/incoming/gallery/blackened-buildings-manchester-before-clean-8727918 https://www.manchestereveningnews.co.uk/incoming/gallery/bla...