PAI (Thailand), April 4 -- After hours spent in the thick pollution-choking parts of northern Thailand, Pon Doikam gets home and blows her burning nose to find blood clots spattered across the tissue.

"It's suffocating," the 36-year-old coconut seller told AFP in Chiang Mai, a tourist destination among the areas affected by dangerous pollution levels this week.

"It feels like you're trapped in the smoke constantly."

Seasonal agricultural burning, forest fires and weather patterns produce an annual pollution season across much of South-east Asia.

But parts of northern Thailand are seeing haze that even hardened locals say is exceptional.

"I've lived in Chiang Mai since I was a kid, and this is the worst it has ever been," said Pon, wh...