Enter concentrations from your sensors or monitoring station. Leave fields blank to exclude a pollutant from the calculation. All values in µg/m³ except CO (mg/m³) and O3/NO2/SO2 which accept ppb. The AQHI uses 3-hour averages, so use those where you have them.
Pollutant Sub-Index Breakdown
Full Results Table
| Pollutant | Reading | Guideline | % of Guideline | Risk |
|---|
How to Use This Calculator
Enter concentrations from an air quality monitor, sensor, or Environment Canada monitoring station. PM2.5 and PM10 go in µg/m³. Ozone (O3), NO2, and SO2 go in ppb. CO goes in mg/m³. Leave any pollutant blank to exclude it. The AQHI is defined on 3-hour averages, while the US AQI uses different averaging periods per pollutant, so a single spot reading gives an estimate for both.
Choosing Indoor vs. Outdoor changes the wording of the recommendation. The province appears in the results and adds a short wildfire-season note for BC, Alberta, and Saskatchewan when the reading is in the High range.
The gauge shows Canada's AQHI from 1 to 10+. Below it you'll see the US AQI sub-index for each pollutant. The recommendation card gives specific actions based on the risk category and your location type.
The sub-index bars show which pollutant is driving the index. If PM2.5 dominates, filtration upgrades help most. If O3 is the driver, ventilation timing matters more. Use the related tools below to model mitigation options.
Understanding AQHI and AQI for Canadian HVAC Applications
Air quality indices exist to translate raw pollutant numbers into actionable health guidance. For HVAC professionals in Canada, they're increasingly relevant because building automation systems can use real-time AQHI data to control outdoor air dampers, filter bypass modes, and demand-controlled ventilation. For homeowners, they're the simplest way to decide when to close windows and run an air purifier.
Canada's AQHI: A Health-Risk Composite
Canada began using the AQHI on June 24, 2007, replacing the older Air Quality Index, because a single-pollutant index says little about the combined health burden of typical urban air. Environment and Climate Change Canada's overview of the AQHI describes an index built from the relative health risks of ground-level ozone, PM2.5, and NO2. In the published formula each pollutant contributes its own excess-risk term, the three terms are added, and the total is scaled to 1 through 10+. There is no interaction term, so the index adds the pollutants' risks and does not model synergy between them. O3 and NO2 go in as ppb and PM2.5 as µg/m³, all as 3-hour averages, and the result is rounded to a whole number with a minimum of 1. During a wildfire smoke event ECCC switches to a PM2.5-only hourly calculation, which this calculator does not do: it always uses all three pollutants. The AQHI is published on Environment Canada's local air quality pages and in the WeatherCAN app. The PM2.5 calculator on this site models the indoor-outdoor relationship in more detail.
How AQHI Risk Categories Work in Practice
An AQHI of 1 to 3 (Low) means everyone can enjoy their usual outdoor activities. At 4 to 6 (Moderate), the general population can carry on unless symptoms such as coughing or throat irritation appear, and people at risk should consider reducing or rescheduling strenuous outdoor activity if they have symptoms. At 7 to 10 (High), people at risk should reduce or reschedule strenuous outdoor activity, and the general population should consider doing so if symptoms appear. Above 10 (Very High), the general population should reduce or reschedule strenuous outdoor activity and people at risk should avoid it. People at risk include children, people over 65, and those with health conditions. During major wildfire smoke events the index can climb to 10+ and stay there for extended periods, which is when a sealed building with HEPA filtration offers the most protection. See the air purifier sizing calculator for room-level protection sizing.
US AQI vs. Canadian AQHI for HVAC Controls
Many commercial building automation systems import US AQI data because more third-party APIs carry it than carry AQHI. The key difference is that AQI reports the worst single pollutant on a 0 to 500 scale, while AQHI adds the risk from three pollutants on a 1 to 10+ scale. For damper and ventilation control logic, that matters: an AQI of 150 (Unhealthy for Sensitive Groups) driven by O3 calls for a different response than an AQI of 150 driven by PM2.5. With PM2.5, closing outdoor air dampers and increasing recirculation filtration is usually the right response. With O3, a gas that particle filters do not capture, extra filtration helps little, and the lever is when and how much outdoor air comes in. The demand-controlled ventilation calculator covers the occupancy-based side of outdoor air control, which is the baseline these air-quality overrides work against. Controls that can read pollutant-level AQI data rather than only the headline number can tell these cases apart.
Indoor Air Quality and Index Limitations
Both AQHI and AQI were designed for outdoor ambient air, and EPA describes the AQI as its tool for communicating about outdoor air quality and health. Used with indoor sensor readings, they give a useful approximation of the health burden of infiltrated outdoor pollutants, but they don't capture indoor-specific concerns like CO2 buildup, VOCs from materials, or biological contaminants. Use this calculator for the outdoor-pollutant component of indoor air quality, and pair it with the IAQ calculator for a complete picture. Averaging periods matter too: the AQHI uses 3-hour averages, while the US AQI uses 24-hour averages for particles, 8-hour averages for O3 and CO, and 1-hour averages for NO2 and SO2, so a single spot reading in this calculator is an estimate for both. Low-cost optical PM2.5 sensors can also over-read at high humidity, so treat their readings as approximate unless the sensor applies a humidity correction.
Wildfire Smoke Season in Canada
Wildfire smoke drives many of the worst air quality events in Canada. The calculator's Wildfire Smoke example (PM2.5 95 µg/m³, O3 45 ppb, NO2 12 ppb) returns an AQHI of 8 (High) and a US AQI of 179 (Unhealthy), driven by PM2.5. With O3 at 30 ppb and NO2 at 10 ppb, PM2.5 has to reach about 86 µg/m³ to round up to AQHI 7 and about 167 µg/m³ to pass 10. Those are figures from the standard three-pollutant formula, and ECCC's PM2.5-only smoke calculation can report different values for the same air. Indoors, the strongest protection combines a tight building envelope, the highest-rated duct filter the system can handle, and a HEPA room purifier running continuously. The blower door calculator covers envelope airtightness, which sets how much smoke leaks in. See the air filtration calculator for duct filtration sizing.
Frequently Asked Questions
Canada's Air Quality Health Index (AQHI) is a 1 to 10+ scale that Environment and Climate Change Canada introduced in 2007 to replace the earlier Air Quality Index. Unlike the US AQI, which scores each pollutant separately, the AQHI adds together the health risk from ground-level ozone (O3), nitrogen dioxide (NO2), and fine particulate matter (PM2.5), using 3-hour average concentrations, and rounds the result to a whole number. An AQHI of 1 to 3 is Low, 4 to 6 is Moderate, 7 to 10 is High, and above 10 is Very High. See the pollutant concentration calculator to model how pollutant levels change over time.
The US AQI ranges from 0 to 500 and reports the worst single pollutant sub-index from PM2.5, PM10, O3, NO2, SO2, and CO. Canada's AQHI uses a combined health-risk formula for three pollutants on a 1 to 10+ scale. AQI highlights the pollutant that sits highest against its standard while AQHI adds the risk from all three. For HVAC automation, knowing which pollutant drives the AQI matters more than the headline number alone, since PM2.5-driven events call for a filtration response while O3-driven events call for changes to outdoor air timing.
AQHI combines PM2.5, O3, and NO2, so there's no fixed PM2.5 value that always produces AQHI 7. With O3 at 30 ppb and NO2 at 10 ppb, this calculator reaches AQHI 7 (High) at a PM2.5 of about 86 µg/m³ and passes 10 (Very High) at about 167 µg/m³. With no O3 or NO2 the same steps take roughly 135 and 213 µg/m³. Environment and Climate Change Canada advises people at risk to reduce or reschedule strenuous outdoor activity at AQHI 7 or higher. During wildfire smoke events ECCC uses a PM2.5-only calculation, so official values can differ. Use the PM2.5 calculator to model indoor concentration from outdoor levels.
Yes, with caveats. AQHI and AQI were designed for outdoor ambient air, but the concentrations are still a useful yardstick indoors. Indoor CO2, VOC, and humidity aren't part of either index, so use the IAQ calculator for a complete indoor air quality score. Low-cost optical PM2.5 sensors can over-read at high humidity, so treat indoor readings as approximate unless your sensor applies a humidity correction. This calculator is most useful for evaluating indoor readings of outdoor-sourced pollutants like wildfire smoke or traffic exhaust that have infiltrated the building.
Related Air Quality Tools
Model indoor PM2.5 from outdoor levels and filtration
Composite indoor air quality score
Model pollutant buildup and decay
Size purifiers for wildfire smoke
Multi-stage HVAC filter efficiency
CO buildup and ventilation sizing