THE NORTH was once again choking under dangerous levels of PM2.5 dust particles yesterday. For instance, tambon Wiang Phang Kham in Chiang Rai’s Mae Sai district cited the day’s peak at 128 micrograms (mcg) per cubic metre of air, more than double the Thai safety limit of 50mcg. As of 11am, the district also hit 238 in its Air Quality Index score (AQI), more than double the safety limit of 100.