Yes, I just rode part of the Mae Hong Son Loop and there were fires all over the place, one of which nearly melted my polyester shirt. The AQI in Mae Hong Son was amongst the worst I've ever experienced aside from the fires in the Okanagan last summer.
The air quality improved on the road to Mae Sot, but there were freshly burned areas along the road for much of the distance.
I just spent the last 18 days riding through Issan and north to Pai, then down to Ayutthaya where I am tonight. There were plenty of nice places in Issan, something that shocked me after reading so many comments like the one above.
The only 2 places I disliked were Phitsanulok and....Chiang Mai! The word sh it hole was precisely what came to mind for both places. CM had air like Mordor and the traffic of Bangkok. The place is cheap for a reason. This was my second trip to CM, the last one being 18 years ago and that visit,too, was cut short due to the terrible air quality.