Anecdata. I lived there for much of that period. The change in air quality itself was real but too subtle to be noticeable. But the change in the amount of car traffic in Paris has been very noticeable, and very impressive.
Some context. The municipal setup gives residents of Paris proper (the 2 million people within the ring road in the image) a lot of influence over the whole Paris region. And 2/3 of those central residents do not own cars! Meanwhile, as in any city, much of the car traffic is generated by suburban drivers. Some of these drivers don't have good transit options, but most of them do. Paris has one of the world's densest transit systems, and that includes the suburbs. Moreover, the suburbanites have always denied the trade-off between housing space and convenience. Yes, the people in central Paris tend to be a bit richer, but they've also accepted the sacrifice of living in small apartments and foregoing private transport. One study found that the average resident of central Paris walks around 2km per day.
So those central Paris residents voted, again and again, to take space away from cars and to give it to bike lanes and sidewalks and parks instead. The local green party has been instrumental, it attracts 10 or 15% of the vote and is a part of the city's coalition government. I was one of those voters. This is the result. It's been positive for the whole city and it's a genuine good news story.
