Having visited this city in winter, I'm used to the smell of the toxic brew in the air, especially during periods of temperature inversion between the hills. Simply price in the cost of an air filter to the rental, spend as much time as possible near it, and when outdoors, mask up with a finely spun cotton weave. (I started using shemaghs during Covid, even before masks went into wide production, and kept on with the Jedi vibe until it inarguably had become a political symbol.)
I'm mystified, though, as to why it hovers over areas in the old town during summer. It's not the fires in the distance, and it's not the industry. But this place is very far from California. My first place here was across from the pharmaceuticals plant, and in addition to the occasional clouds (when you locate a plant at the bottom of the valley, presumably for rail access, smokestack height gives you diminishing returns), on one or two occasion, particulates in the forms of caplets came down.
So, it's not California (continental purity), or Germany (strict regulation), but if you keep vigilant as to exposure, it's still fairly idyllic.
My last two Humble Quarters were extremely humble, for many reasons, so I'm consciously balancing that out with one or two stays that are closer to the usual median (well below US, and also well below tourist averages in the regions -- when you can look across many countries to find the most logical accommodations, you can usually find a discount or two). If you book a string of extremely spartan quarters (no washing machine, etc.), the travelling conditions can start to deteriorate, and the ability to work suffers. Still hewing to a strict budget -- the quintessential 'tomato tourist.'
(But none of those this week, as the other vegs were on sale. Might splurge on some cheap cheese next weekend.)