The Chiang Mai Air Quality is quite Good and Clear for most of the year. During the Rainy Season (early June to early October), there are Frequent Brief Showers which wash the Air and leave it with a clean smell. During the Winter Season (late October to the end of February) the air is clean and crisp.
There are some minor problems on the major roads during the Morning and Evening Rush House. This is common with every city. There is very little Industrial Pollution in or around Chaing Mai.
During the Late Dry Season - Summer (February, March, and maybe the beginning of April) is a different matter. The Thai’s clear the Rice Fields for planting through Burning. There is also Extensive Indiscriminate Forest and Yard Waste Burning which creates a Smoky Haze which is held in by the Mountains surrounding Chiang Mai. When the winds are from the South, there is Clear air but when the winds are from the North, we get Haze.
The Heavy Particulate Count irritates people with Respiratory Problems, especially people with Asthma or Emphysema.
Contact the Polution Control Department - Regional Air Quality Data for Daily Air Quality information. For a list of the Daily Air Quality Results for the last year, contact the Polution Control Department - Summary Daily Data for Several Years.
The solution that some people use is to visit the Beaches of Southern Thailand if the Air becomes difficult to breath. Also, Air Proofing your House and using Hepa Air Filters may be able to make the indoors tolerable during this period.
There are several Initiatives from the Government and the King which are underway to Educate the Thai’s about the results of their behavior and the results of their actions but they have not yet born fruit.