By Tossapol Boonpat
The PM10 level of small dust particles in the air in the northernmost province reached 148 micrograms per cubic metre, well above the 120 micrograms considered safe to breathe.
On Sunday it was 129mg, on Monday 147 and on Tuesday 133, according to the Pollution Control Department’s haze-monitoring report website (air4thai.pcd.go.th).
The level in Chiang Mai’s Mae Chaem district was 147mg on Wednesday morning, and in Muang Nan 174mg.
Forest fires – the key contributing factor – are burning in several areas of Mae Hong Son, where steep mountains impede or block fire-fighting efforts. Fires are sometimes so remote they can only be left to burn themselves out.