Health Canada residential guidelines

Canada publishes a series of residential indoor air-quality guidelines covering individual pollutants, separate documents for NO₂, PM_2.5, CO₂, formaldehyde, ozone, mold, and several others. They are not regulatory limits in the U.S./EPA sense, but public-health authorities use them as a reference when they assess indoor air.

The most-cited numbers are for residential NO₂: 90 ppb (170 µg/m³) as a 1-hour limit and 11 ppb (20 µg/m³) as a 24-hour limit. The 24-hour value is far below the U.S. EPA's outdoor annual standard of 53 ppb; Health Canada based it on respiratory symptoms in children with asthma. Terrestream cannot check these numbers: its NO_x index shows combustion events, not an NO₂ concentration.

For PM_2.5, Health Canada's residential guidance sets no numeric limit: indoor levels should be kept as low as possible and, at a minimum, lower than outdoors. For CO₂, the residential guideline sets a long-term limit of 1,000 ppm as a 24-hour average.

Terrestream has no Health Canada preset: everyone gets the same firmware bands. Two things help Canadian readers. The device can show its index as AQHI+, the PM_2.5-only form of Canada's Air Quality Health Index, instead of the EPA-scale IAQ; you pick it in the app's device settings, and it is the default when the device language is set to Canadian French (see Canadian AQHI). And you can compare readings with these guidelines yourself: CO₂ against the 1,000 ppm 24-hour limit, and indoor PM_2.5 against the outdoor level.