I remember my first trips to Europe. I was from a suburban (although not connected to an urban center) town in the Midwest USA. After a few days in the city my eyes were red and itchy. Took me a bit to figure out it wasn't allergies to something new... it was just the vehicle exhaust.
The smell of diesel exhaust still makes me think of London, Paris... etc. Somehow that imprinted on me. They're actually good memories, but just an unusual spell to associate them with.
Stockholm is built on islands that helps, and the rains are not frequent but heavy enough to clean the city a bit, waste management is good. Thera are also fewer people are active in the center of Stockholm compared to Paris; Stockholm 5 214 pop/km², Paris 20 909 pop/km² (this disregards important factors about how those numbers work, but it's an interesting indication.)
I notice it's worse in cities with extremely dense urban cores, like NYC. There was a distinct smell (not just garbage, but something I basically call 'the NYC smell' in my head) in many parts. Other cities never seemed quite so bad; at least not bad enough I can still remember that smell.
Maybe Stockholm has plenty of wind? Big cities tend to stink. Didn't bother me until my 30s, now I can barely tolerate the smell, not just the fact that it kills us.
But hey, people want cars. Lots of dirty but cheap cars. Almost nobody seems to care. It's just the nature of living in a poor country I guess.
I think cars generally contribute to bad smells, and poor waste management infrastructure can also contribute to bad smells (think garbage bins out on streets instead of enclosed, for example)
It's situated on an archepilago in the Baltic sea. Sure, it might be less windy than other coastal cities, but Stockholm is far windier than cities in-land.
Stockholm has tolls to reduce road congestion though. The place was definitely smellier back in the 90's.
I get this after I spend a few days at my parents' house and go back to Paris, and they live only 50 km away.
I feel this quite strongly since I get around by motorcycle, so I don't have the benefit of filters and whatnot that cars have.
Whenever I do this, I keep wondering what the lungs of people commuting every day look like, since I get a dry cough even when traffic isn't all that dense.
The smell of diesel exhaust still makes me think of London, Paris... etc. Somehow that imprinted on me. They're actually good memories, but just an unusual spell to associate them with.