Chimneys
I can remember smog when I was a child. A toxic mix of fog and smoke, pouring from thousands of chimneys, it could reduce visibility to a few feet and induce a deadly suffocation. Chimneys abounded in the UK until the introduction of various clean air legislation rendered their use illegal.
I’m not sure if the prominent red and white funnels releasing steam from the bowels of New York City (below) qualify as chimneys but they perform a similar function to their higher up cousins.
Old chimneys (below) compete with an even older spire of Christ church, Spitalfields.