Much of the North and upper Northeast was cloaked in fine-dust smog on Wednesday, with residents advised to stay indoors.
The Geo-Informatics and Space Technology Development Agency reported at 3pm that 14 of the kingdom's 77 provinces were blanketed with red (seriously harmful) levels of particulate matter 2.5 micrometres and less in diameter (PM2.5).
Readings ranged from 75.3 to 117.5 microgrammes per cubic metre of air over the past 24 hours. The government's safe threshold is 37.5µg/m³.
The worst level was recorded in the northern province of Lampang. Most of the other affected provinces were in the North. They were Phrae (114.6µg/m³), Lamphun (108.7), Sukhothai (103.7), Chiang Mai (101.0), Nan (93.7), Uttaradit (92.0), Mae Hong Son (91.4), Tak (82.8), Phayao (82.6) and Phitsanulok (78.1).
In the upper Northeast, the red levels were in Loei (102.3), Nong Khai (82.9) and Nong Bua Lam Phu (75.3).
The Chiang Mai office of the Pollution Control Department advised people to stay indoors because the smog was accumulating in the stagnant air.
Twenty-two other provinces reported orange (initially harmful) levels of PM2.5. Most of them were in the lower Northeast and the central Northeast.
The Gistda map shows the North and the upper Northeast were shrouded with red levels of PM2.5 on Wednesday afternoon.