How bad was pollution in Europe during the height of the Industrial Revolution?

I would suggest x - posting this to /r/askscience there are a number of proxies that can be used to investigate the characteristics of the climate and atmosphere throughout the Industrial revolution and their rates of change and a proper understanding of these requires literacy in climate sciences.

Examples would be things like Greenland Ice Cores which show a dramatic increase in atmospheric Co2 in the 19th c.

The evolution of the peppered moth which developed a darker colour in urban, polluted areas, the general consensus is that this was an anti-predation camouflage adaptation as the trees it rested on were blackened by soot, but this isn't uncontroversial.

Tree ring data can tell you a lot about things like seasonal rainfall variation, which in turn tells you a lot about the climate.

One certainly gets the impression from sources from this period that they perceived pollution to be a major issue Blake's 'dark satanic Mills', Dickens' foggy London streets, Turners oddly coloured skies.

But if you're looking for an accurate, falsifiable comparison between 19th c. Europe and Europe today (or Beijing) then /r/askscience is probably your best bet.

Also it's worth noting here that not all the 19th c. air pollution was linked to the Industrial revolution and population growth, the eruption of Krakatoa in 1883 also had a major impact on the global climate.