Canada does not use the U.S. EPA AQI. Instead, Environment and Climate Change Canada publishes the Air Quality Health Index (AQHI): a 0 to 10+ scale derived from the combined health impact of ozone, NO2, and PM2.5 rather than the worst-of-many that EPA uses. The design origin paper by Stieb et al. explains the rationale.
The formula combines short-term mortality risk per unit of each pollutant, weighted by the local pollution mix. The result is a single number that is more directly interpretable as a health-risk indicator than the threshold-band-based EPA AQI. Bands: 1-3 Low risk, 4-6 Moderate risk, 7-10 High risk, 10+ Very High risk. Each band has explicit recommendations for the general population and for at-risk groups (children, older adults, those with heart or lung conditions). The calculation method is public.
For Terrestream users in Canada, the dashboard's "Canadian AQHI" mode replaces the EPA AQI band with the AQHI value on the outdoor reference card, and recalibrates the cross-reference logic for ventilation suggestions. A "moderate" outdoor AQHI of 5 carries different implications than an EPA AQI of 100; both numbers are accurate, they describe different aspects of the same air.
There is no AQHI equivalent of the IAQ score on the dashboard yet. The IAQ score remains on the 0-500 scale; AQHI as an outdoor reference is the option. Health Canada publishes parallel residential indoor air guidelines (see Health Canada guidelines) that the dashboard uses for indoor thresholds in Canada-mode.
References
- Environment and Climate Change Canada - AQHI www.canada.ca
- Environment Canada - AQHI calculation method www.canada.ca
- Stieb et al. - Origin of the Canadian AQHI pubmed.ncbi.nlm.nih.gov
- Health Canada - Indoor air contaminants overview www.canada.ca
