For those planning on going to Chiang Mai before rainy season begins be aware that the burning season has started quite a bit earlier this year, for a variety of rumored reasons, resulting in very dense smoke and smog in the North.
http://www.thailandoutlook.tv/tan/Vi...DataID=1052715
You can check the PM10 here, use station 35.
http://aqmthai.servehttp.com/public_report.php