Is Canada's AQHI the same as the US AQI?

Short answer: No — they are different indexes on different scales. Canada's Air Quality Health Index (AQHI) runs 1 to 10+ and combines three pollutants into one health-risk number; the US AQI runs 0 to 500 and reports whichever single pollutant is worst. There is no exact conversion, but during wildfire smoke both are driven by PM2.5, so the action bands map cleanly: AQHI 7+ lines up with AQI 151+, and both mean a fitted N95 for sustained time outdoors.

AQHI vs AQI: Canada and US Air Quality Scales Compared

Wildfire smoke does not respect the border, but the numbers describing it change the moment you cross it. A Windsor resident sees AQHI 8 while Detroit, breathing the same plume, sees AQI 180. This guide decodes both systems — what each index measures, why the numbers cannot be converted directly, and how to make the same masking decision on either scale. The respirator side of that decision lives in our wildfire smoke protection guide and the wildfire N95 buyer's guide.

Why this matters.
During the August 2026 smoke event, advisories cover much of Canada and the US Great Lakes and Northeast at once, and cross-border readers are comparing numbers that are not the same scale. Misreading AQHI 5 as "half of AQI 10 — clean air" or AQI 150 as "off Canada's chart" leads to masking too late. Health Canada's wildfire guidance recommends a well-fitting NIOSH-certified N95 outdoors in smoke; knowing your index's trigger band is what makes that advice actionable.

Part 1: How Canada's AQHI works

The Air Quality Health Index is published by Environment and Climate Change Canada as a single health-risk number from 1 to 10, with an open-ended 10+ band for extreme events. It is computed from the combined health impact of three pollutants measured over a rolling three-hour window: fine particulate (PM2.5), ground-level ozone, and nitrogen dioxide. The bands carry health messaging rather than pollutant concentrations: 1–3 Low (usual activities), 4–6 Moderate (at-risk groups scale back strenuous outdoor activity; the general population only if symptomatic), 7–10 High (general population reduces or reschedules strenuous outdoor activity; at-risk groups avoid it), and 10+ Very High (everyone limits time outdoors). When wildfire smoke moves in, ECCC layers a Special Air Quality Statement on top of the number, and Quebec communicates through its Info-Smog program. During fast-moving smoke, British Columbia supplements the standard calculation with an hourly PM2.5-based adjustment so the index keeps pace with the plume — one reason BC readings can jump band-to-band within an hour.

Part 2: How the US AQI works

The US AQI takes the opposite approach: each regulated pollutant is scored on a 0–500 scale against EPA concentration breakpoints, and the reported AQI is whichever pollutant scores worst at that hour. The categories are Good (0–50), Moderate (51–100), Unhealthy for Sensitive Groups (101–150), Unhealthy (151–200), Very Unhealthy (201–300), and Hazardous (301+). In a wildfire smoke event the driving pollutant is almost always PM2.5, and the number to watch is AirNow's NowCast — a weighted recent-hours average that reacts to smoke arriving, rather than the flat 24-hour average that lags it. EPA tightened the PM2.5 breakpoints in 2024, so the same smoke now posts higher AQI values than it would have in older charts. What the AQI number triggers for US outdoor workers — including California's Title 8 §5141.1 rule at AQI 151 — is covered in the outdoor-worker section of our wildfire smoke guide, with crew-quantity picks in the construction N95 guide.

Part 3: Why there is no exact conversion — and the mapping that works anyway

The two indexes cannot be converted with a formula because they answer different questions. AQHI blends three pollutants into one relative-risk number calibrated on Canadian health data; AQI reports the single worst pollutant against fixed concentration breakpoints. The same air can legitimately produce different-looking numbers, and outside smoke season (when ozone or NO2 leads) the scales genuinely diverge. But during a wildfire smoke event both indexes are being pushed by the same PM2.5, which is why the action bands align well in practice — the table below is that practical mapping, and it is an approximation by design, not an official equivalence published by either agency. If you track one habit, make it this: check the current hourly reading on your side of the border before outdoor work, and let visible haze plus a smoke smell override a lagging number in either system. The filtration answer is identical in both countries — a NIOSH N95 or better, explained class-by-class in our respirator filter types guide and the N95 vs KN95 vs P100 comparison.

Practical alignment when PM2.5 from wildfire smoke drives both indexes. Approximate by design — neither agency publishes an official conversion.

Part 4: Making the mask decision on either scale

Both countries' guidance converges on the same gear. Health Canada's wildfire smoke pages recommend a well-fitting NIOSH-certified N95 or equivalent respirator for anyone who must be outdoors in smoke — the same instrument US guidance reaches for, and the same picks ranked in our wildfire N95 guide and broader best N95 roundup. At the High band (AQHI 7+ / AQI 151+), put on a fitted N95 for any sustained outdoor exposure; sensitive groups start one band earlier. Above AQHI 10 or into US Very Unhealthy territory, minimize time outside and step up to a sealed elastomeric with P100 filters for outdoor work — the escalation logic in the reusable smoke respirator guide, with full-face respirators the step past that when smoke stings eyes too. Fit is the failure point on both sides of the border: a valid seal check (walked through in how to seal check a respirator) matters more than the number on the box, beards defeat every class equally (respirators and beards), and counterfeits are a cross-border problem — verify approvals per our NIOSH verification how-to. Canadian buyers can use the same product links: Amazon listings on this site automatically redirect to the matching amazon.ca listing where one exists.

Worked example: reading a smoke day in Calgary — with a cross-border check

Prairie smoke has settled over Calgary, and a reader wants to know whether to mask for a day of outdoor work — then compare notes with a colleague in Montana. The sequence:

1. Check the current AQHI, not yesterday's forecast. The ECCC AQHI page shows Calgary at 8 with a Special Air Quality Statement in effect. That is the High band — reduce strenuous outdoor activity, and Health Canada's wildfire guidance applies: a well-fitting NIOSH N95 for time outdoors.
2. Check where the smoke is heading. FireSmoke.ca's forecast shows the plume thickening through tomorrow — so this is a buy-now situation, not a wait-it-out one. N95 stock tightens fastest in the first 48 hours of an event.
3. Pick the mask from the standing ranking. The wildfire N95 buyer's guide picks apply unchanged in Canada: an Aura-style flat-fold for most faces, cup-style for value stocking, all NIOSH-approved and all available on amazon.ca through the same links.
4. Fit it properly. Strap placement and a two-hand seal check per the seal-check guide — at AQHI 8 the seal, not the filter media, decides how much smoke gets in.
5. Translate for the Montana colleague. Calgary's AQHI 8 corresponds to roughly AQI 151-plus territory on the US scale — Unhealthy. The colleague checks AirNow's NowCast, sees 172, and reaches the identical conclusion: fitted N95 outdoors, strenuous work rescheduled.

Two countries, two indexes, one decision — the bands, not the raw numbers, are what convert.

Frequently asked questions

Is Canada's AQHI the same as the US AQI?

No. AQHI is a 1-10+ health-risk index combining PM2.5, ozone, and nitrogen dioxide over a rolling three-hour window; the US AQI is a 0-500 scale reporting the single worst pollutant against EPA breakpoints. Same air, different math.

How do I convert AQHI to AQI?

You can't, exactly — the indexes use different pollutant sets and averaging. During wildfire smoke, when PM2.5 drives both, the practical mapping is AQHI 4-6 ≈ AQI 101-150, AQHI 7-10 ≈ AQI 151-250, and AQHI 10+ ≈ AQI 250 and up.

What does AQHI 7 mean during wildfire smoke?

The start of the High band: the general population should reduce or reschedule strenuous outdoor activity, and at-risk groups should avoid it. For anyone staying outdoors, Health Canada's wildfire guidance points to a well-fitting NIOSH-certified N95.

What AQHI level calls for a respirator outdoors?

Treat AQHI 7 as the trigger for a fitted N95 during sustained outdoor exposure, with sensitive groups starting in the 4-6 band. Above 10, limit outdoor time and step up to a sealed elastomeric with P100 filters for outdoor work.

What does AQHI 10+ mean?

The open-ended Very High band — extreme readings, common near active fires. Everyone should limit time outdoors; strenuous outdoor activity should stop, and outdoor work warrants a sealed respirator rather than a disposable.

Why does British Columbia's AQHI behave differently in smoke?

BC supplements the standard three-pollutant calculation with an hourly PM2.5-based adjustment during smoke events, so its readings react faster when a plume arrives — you may see the index jump several bands within an hour.

What is a Special Air Quality Statement?

Environment and Climate Change Canada's advisory layer: a bulletin issued when air quality is or is expected to become degraded, most often for wildfire smoke. It names the affected regions and accompanies the AQHI number rather than replacing it.

What is Info-Smog in Quebec?

Quebec's own air-quality communication program, referenced by Health Canada alongside the AQHI. Quebec readers should follow Info-Smog advisories during smoke events; the masking thresholds in this guide apply the same way.

Does the AQHI measure wildfire smoke directly?

It measures smoke through its PM2.5 component — smoke is overwhelmingly fine particulate. Ozone and NO2 also feed the index, which is one reason a formula conversion to the PM2.5-focused smoke AQI doesn't exist.

What is the NowCast AQI and why does it matter in smoke?

AirNow's NowCast weights the most recent hours instead of averaging a full day, so it tracks smoke arriving in real time. During fast-moving events the NowCast is the US number to act on — the 24-hour average can lag a plume by half a day.

Do US air-quality apps work in Canada?

Many popular apps and sensor networks display a US-style AQI computed from Canadian monitoring data, so you may see both numbers for the same city. Both describe the same air — just apply each number to its own scale's bands.

Does Canada officially use the US AQI anywhere?

No — the AQHI is Canada's national index, with provincial variants like BC's smoke-adjusted calculation and Quebec's Info-Smog messaging. US AQI values you see for Canadian cities come from third-party apps, not Canadian agencies.

Which respirator for AQHI above 10 or AQI above 250?

For necessary outdoor work in that range, step past disposables to a half-face elastomeric with P100 filters and verified seal; limit exposure time regardless. The reusable smoke respirator guide covers the specific models.

Do Canadian workplaces have an AQHI trigger like California's AQI 151 rule?

Not as a bright-line number. California's Title 8 §5141.1 mandates respirator provision at PM2.5 AQI 151+; Canadian provinces regulate wildfire smoke through general hazard-assessment duties, with respirator selection following CSA Z94.4 and the same NIOSH approvals.

Where can I see where wildfire smoke is heading next?

FireSmoke.ca maps forecast surface smoke across North America, ECCC's AQHI pages carry Canadian forecasts and Special Air Quality Statements, and AirNow's Fire and Smoke Map covers the US side with monitor and sensor data.

Further reading on this site

• Wildfire Smoke Protection: The Complete Safety Guide — the full playbook — AQI thresholds, fit, indoor air, and the Canada module this guide extends
• Best N95 Masks for Wildfire Smoke (2026) — the ranked picks, all NIOSH-approved and amazon.ca-available
• Best Reusable Respirators for Wildfire Smoke — the elastomeric step-up for Very High readings
• N95 vs FFP2 vs FFP3 — the US-EU certification bridge, same jurisdiction logic as this guide
• How to Seal Check a Respirator — the 10-second check that decides real-world protection
• Disposable respirator collection — N95 and P100 filtering facepieces with approvals listed
• Respiratory protection collection — the full range when smoke season calls for more than a disposable
• CSA Z94.4: Canada’s respirator standard — the program rules behind Canadian smoke-season and workplace respirator use.