Airborne PM2.5 dust reached the health-threatening Red level in eight northern provinces Thursday morning, with Mae Hong Son being the hardest hit.

According to real time satellite-derived air pollution data via the “Check Foon” application, PM2.5 readings in the eight northern provinces are: 211.9 microns (µg/m³) in Mae Hong Son, 132.3µg/m³ in Chiang Mai, 111.5µg/m³ in Lamphun, 102.7µg/m³ in Chiang Rai, 92µg/m³ in Tak, 84.5µg/m³ in Phayao, 83.2µg/m³ in Lampang and 77.3µg/m³ in Nan.

PM2.5 levels in 25 other provinces also exceed the 37.5µg/m³ safety threshold or Orange level, but air quality in Bangkok today is described as good to very good.

Meanwhile, a resident of Chiang Mai said in her Facebook post today that she wonders why her air purifiers, which were sent for cleaning about a month ago, often show Red level readings. So, she decided to open one and found that the filter was clogged with dust, despite the fact that her house is far from the main road and she does not smoke.

She claimed that there are 20 air purifiers in her house and they to be appear unable to cope with the current levels of the air-borne dust.