What you can do:
* If you are traveling for fun, don't visit places with execrable air quality. Choose somewhere nice. Bonus points if you tell the clean city why you chose it and your dirty discards why they failed your selection process. They won't care about your health, but they do care about your money. If enough people avoid the shitholes, maybe they'll clean up their act.
* Some places have highly variable air quality for seasonal reasons. If you must visit these, try to do so during the time when the air is more breathable, and avoid the worst pollution period.
* If you must travel somewhere filthy, take extra precautions to reduce the damage, such as wearing a filter mask. Minimize physical exertion and allow extra time for things like walking. These are not good places for outdoor physical activities such as hiking or biking.
* People with lung problems, pregnancy, or other sensitivities to air quality should be extra-extra careful. Avoid filthy cities if at all possible. Make sure you have your medication(s) with you. Check what medical support will be available at the destination in case of crisis (this happened to some people in the study). Carrying emergency oxygen may be advisable. Consider talking with your doctor about safety precautions.
* And for fucksake, pay attention to indoor air quality too. Don't invite, or worse yet drag, your contaminant-sensitive friends or relatives to your house during renovation when it is full of dust, fumes, and devil-knows-what else. Make sure people know if you have furry pets to which they may be allergic. Zero fun is had when someone feels like crap and can barely breathe. Either choose another time, or choose another venue.
* To improve air quality in your municipality: Support regulations for cars, factories, etc. that limit or eliminate pollution. Maximize greenspace, especially including large trees to help clean the air. If you live in fire-prone areas, take steps to reduce the risk of wildfires.
A lot of problems are things that individuals can't really influence, but this one has a lot of levers within most people's reach. Use them wisely.