Every year, from February through April, "slash-and-burn" farming in the countryside surrounding Bangkok fills the air with smoke, the British newspaper The Guardian reported Friday.
This year, air pollution levels in Thailand's Mae Hong Son and Chiang Mai provinces have recently reached levels as high as 431.6 micrograms per cubic yard, far beyond Europe's and the United States' 50 microgram-per-cubic-yard limit.
A Tourism Authority of Thailand spokesman said slash-and-burn farming has been outlawed but there has been little effort to stop the practice.
Mark Ord, who runs All Points East, which organizes treks in the region, said he has been advising potential travelers to stay away.
"I've never seen it this bad and have even been advising visitors to stay away. Remember, you are dealing with a government whose health minister recently tried to blame the rise in dengue fever on 'women wearing hot pants,'" he said.