when the traffic light turned green, a big cloud of pollution rose and takes a few minutes to dissipate. That has been reduced greatly, with just a little cloud due to some motorcycles.
In the old days, if I needed to walk on a main road, I would be sure to walk up-wind. Now, I no longer notice.
From tall buildings, the air would be clear at sunrise but by noon it was difficult to see more than a few kilometers. Now, it stays pretty clear all day.
If you have respiratory problems, then you may still want to go live by the seaside or in the suburbs, but many people with respiratory problems are OK in Bangkok.