📊 AQHI Value
⚠ Risk Category
Pollutant Contribution
Full Calculation Table
| Pollutant | Concentration | Relative Risk Factor |
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How to Use the Air Quality Index Calculator
Enter current PM2.5, ozone, and NO2 readings from a local air quality monitoring station, or use one of the quick reference scenarios.
Click Calculate AQHI to see the combined index value, risk category, and which pollutant is contributing most to the result.
Use the risk category to decide whether to adjust ventilation, close windows, or run mechanical filtration more aggressively.
How Canada's AQHI Differs From a Single-Pollutant Index
Environment and Climate Change Canada, working with health authorities, built the Air Quality Health Index to communicate health risk rather than to track a single regulatory limit. The AQHI combines fine particulate matter, ground-level ozone, and nitrogen dioxide into one formula calibrated against actual health outcome data. The result is a number from 1 to 10, with values above 10 reported as 10+ during severe pollution events like major wildfire smoke episodes. The bands are Low (1 to 3), Moderate (4 to 6), High (7 to 10), and Very High (above 10).
Why Combine Three Pollutants
Real air pollution rarely comes from just one source. Wildfire smoke drives PM2.5 sharply higher, vehicle traffic contributes both NO2 and ozone precursors, and summer heat and sunlight push ground-level ozone up on otherwise clear days. A single-pollutant index can understate the combined health burden when several pollutants rise together, which is part of why the AQHI integrates all three into a single number. Each pollutant adds a term of the form e^(k × concentration) − 1, with k set at 0.000871 for NO2, 0.000537 for ozone, and 0.000487 for PM2.5. The sum is then multiplied by 100 × 10/10.4 and rounded to a whole number for reporting.
Particulate Matter Usually Dominates Wildfire Events
During wildfire smoke events, PM2.5 can push the AQHI into its highest categories almost on its own while ozone and NO2 stay near typical levels. The Wildfire Smoke Event preset shows it: 100 µg/m³ of PM2.5 with 35 ppb ozone and 10 ppb NO2 works out to about 7.5, reported as 7 (High), and PM2.5 supplies roughly 64% of the total. The Severe Smoke Episode preset, at 250 µg/m³ of PM2.5, lands near 15.5 and reports as 10+. The calculator shows which pollutant contributes most to a given result, which is useful context on a smoky day. If smoke has already reached the building, a portable cleaner sized by CADR is the quickest backstop, and the air purifier sizing calculator turns room size and a target ACH into the CADR to look for.
What This Means for Mechanical Ventilation
At higher AQHI levels, the goal is to cut how much outdoor air, and the pollution in it, enters the building. Health Canada's Guidance for Cleaner Air Spaces during Wildfire Smoke Events advises switching to recirculation when outdoor air is poor and returning to fresh air intake once the plume passes. Be careful with the bypass setting on an HRV or ERV: it routes outdoor air around the core, so it does not reduce intake. Use the unit's recirculation or standby mode, or turn it off for the duration, then check your settings against the HRV calculator or ERV calculator. If outdoor air stays reduced for more than a few hours, track indoor carbon dioxide buildup with the CO2 calculator.
Filtering the Outdoor Air That Still Comes In
Any ventilation that continues during a smoke event should pass through the best filter the system can handle. MERV 13 or higher is the usual target for fine particles, but a denser filter adds pressure drop, and a blower that was sized for a MERV 8 can lose airflow with a MERV 13 in its place. The MERV rating calculator compares efficiency by particle size and estimates the pressure drop against your available static pressure, so you can check the trade before you buy filters.
This Calculator Needs Current Readings
This tool does not pull live data on its own. Enter current concentrations from a local monitoring station, commonly available through Environment and Climate Change Canada or a provincial air quality network, to get a result that reflects conditions where you actually are. The published AQHI is built from 3-hour average concentrations, so use averaged readings if you want your result to line up with the official number for your area.
Frequently Asked Questions
The Air Quality Health Index, or AQHI, is the air quality scale Environment and Climate Change Canada uses to communicate health risk from air pollution. Unlike indexes built around a single pollutant, the AQHI combines fine particulate matter, ground-level ozone, and nitrogen dioxide into one number on a scale of 1 to 10+, where Low is 1 to 3, Moderate is 4 to 6, High is 7 to 10, and Very High is above 10.
The American Air Quality Index reports the single pollutant currently posing the greatest risk and scales numbers up into the hundreds. Canada's AQHI instead combines three pollutants into a single formula and reports a smaller number, from 1 to 10 or higher, calibrated directly against health risk rather than against a regulatory concentration limit for any one pollutant.
At higher AQHI levels, keep windows closed and let filtered mechanical ventilation do the work. If your HRV or ERV has a recirculation or standby setting, use it, or turn the unit off until the smoke passes, because the bypass setting still draws outdoor air into the building. Health Canada advises switching to recirculation when outdoor air is poor and using a MERV 13 or better filter where the system can handle it. Return to normal operation once the plume clears so indoor carbon dioxide and humidity do not build up.
This calculator does not pull live data automatically. Enter current readings from a local air quality monitoring station, often available through Environment and Climate Change Canada or a provincial air quality network. The published AQHI is built from 3-hour average concentrations, so averaged readings will match official values most closely.