"remarked that the smuts in London were not quite so bad as they used to be"
by cm

Parliament, Effect of Fog (1904)
Public DomainParliament, Effect of Fog (1904) - Credit: Claude Monet
Air pollution in nineteenth century London, resulting from hundreds of thousands of domestic coal fires, was so bad that health, visibility, buildings and washing lines all suffered.  In Bleak House (1853), Charles Dickens wrote, "Smoke lowering down from chimney-pots, making a soft black drizzle, with flakes of soot in it as big as full-grown snow-flakes — gone into mourning, one might imagine, for the death of the sun."  The word smog (combining smoke and fog) was not coined until the end of the nineteenth century, but the reality of the phenomenon was inescapable for Victorian Londoners.

A really bad nineteenth century fog appeared early in the morning as a thick white mist, like the country fog, only dirtier. With the lighting of the fires it would soon become yellow and pungent, irritating the throat and eyes, till midday the continued outpouring of chimney products would have turned the fog a sooty brownish black causing the darkness of night. -- L.C.W. Bonacina

The problem of "pea soupers" continued into the twentieth century, culminating in the Great Smog of 1952, which may have caused as many as 12,000 fatalities due to respiratory problems.  The Clean Air Act 1956, which banned coal fires in many cities and relocated power stations away from urban areas, finally brought an end to serious smog in London.