The 9-seater Beechcraft King Air 200 transporting US Chargé d’Affaires Michael Heath, the acting ambassador, was about to land at Mae Hong Song airport at 9.05am but low-lying smog prevented the pilot from seeing the runway.
He decided to abort a landing and returned to Chiang Mai International Airport to wait for the visibility to improve later in the day.
Heath was scheduled to co-chair a ceremony with the Mae Hong Song deputy governor to launch a project to conserve ancient coffins in a cave in Pang Ma Pha district.
The conservation project by Silpakorn University’s Faculty of Archaeology has received a US$220,000 (THB7.17 million) grant from the US Ambassador’s Fund for Cultural Preservation. Heath was supposed to officially hand over the grant to Prof Dr Rasamee Chusongdej, an archaeologist of the faculty.
The acting ambassador eventually cancelled his plan to travel to Mae Hong Son and instead visited the Royal Thai Navy's earthquake monitoring centre on Doi Suthep.
The Mae Hong Son Meteorological Office reported that visibility over the province was poor from 6am to 10am.
The station monitoring air pollution in tambon Jong Kham, Muang district, said PM2.5 particles were measured at 98 micrograms per square cubic metre of air, which was higher than the safety standard.
The Meteorological Office reported that several hot spots were detected in Northern provinces, apparently from weed burning and from wildfires in Myanmar, resulting in the low visibility and a higher amount of PM2.5 pollutants.