I grew up in Paris. When I was little, Paris was gross. The air was really polluted. The infamous caniveaux had dirty water with trash sliding past you while you waited for the light to cross, and when it rained, the water pooled at crosswalks such that you had to step in it and couldn't avoid it. You could never go into cafe bathrooms, they were so disgusting.
Consecutive generations of left-leaning mayors have created bus lanes, booted cars out of some parts of the city and significantly reduced pollution levels, and I feel the difference in the air. Paris has realized the necessity of tourists and has cleaned up its bathrooms, streets and hotels. It may not look particularly clean compared to other capital cities, but it's SUCH AN IMPROVEMENT compared to what it used to be!