Air quality is a challenge in Northern Thailand, specifically during burning season: December to April.
The ultimate burning season survival guide on vegancampthailand.com.
Near Lek & Greg Vegan Camp: https://www.meteoblue.com/en/weather/forecast/airquality/ban-li-luang_t… - It might be better here away from the city.
Air purifiers in Chiang Mai, Thailand: https://www.vogair.com/
Lek & Greg Vegan Camp GPS coords lat long: 17°47'45.42"N ; 98°57'45.34"E
2019-02-14: Rot Dang black smoke: Calls for schools in Chiang Mai to close as haze crisis worsens
2019-02-13: Chiang Mai third most polluted city
2019-02-06: Sprinkler walls: PM Prayut targets diesel cars, factories