AQHI vs AQI: Canada and US Air Quality Scales Compared
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.
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.
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.
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.
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.
| AQHI (Canada) | Risk category | ≈ US AQI during smoke | Action for the general population | Mask guidance |
|---|---|---|---|---|
| 1–3 | Low | 0–100 (Good–Moderate) | Usual outdoor activities. | No mask needed. |
| 4–6 | Moderate | ≈ 101–150 (Unhealthy for Sensitive Groups) | Reduce strenuous outdoor activity if symptomatic; at-risk groups act now. | Sensitive groups wear a fitted N95 for extended outdoor time. |
| 7–10 | High | ≈ 151–250 (Unhealthy and above) | Reduce or reschedule strenuous outdoor activity. | Fitted N95 for any sustained outdoor exposure. |
| Above 10 | Very high | ≈ 250+ (Very Unhealthy–Hazardous) | Avoid strenuous outdoor activity; limit time outside. | Sealed respirator outdoors; P100 elastomeric for outdoor work. |
Practical alignment when PM2.5 from wildfire smoke drives both indexes. Approximate by design — neither agency publishes an official conversion.
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:
- 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.
- 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.
- 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.
- 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.
- 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 — 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.
What is Why there is no exact conversion?
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.
What is worked example?
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:
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.
Why trust this guide? WC Safety is an independent PPE review site: we verify NIOSH approval numbers before recommending any respirator, and every air-quality claim in this guide is cross-referenced against the Health Canada, ECCC, EPA, and BC government source pages linked throughout.
Authored by Steven Eaton, WC Safety Editorial — independent PPE researcher covering respiratory protection standards and North American air-quality guidance.
Last reviewed: · Sources reviewed: Health Canada wildfire smoke guidance, ECCC Air Quality Health Index pages, EPA AirNow AQI documentation, BC air quality warnings, California Title 8 §5141.1.
Editorial standard: Zero sponsored listings. No manufacturer input. No paid placement on this page. Band thresholds and health messages are quoted from the publishing agencies; the AQHI-AQI mapping is labeled an approximation because no official conversion exists, and we say so rather than inventing one.
Last reviewed: · Sources reviewed: Health Canada wildfire smoke guidance, ECCC Air Quality Health Index pages, EPA AirNow AQI documentation, BC air quality warnings, California Title 8 §5141.1.
Editorial standard: Zero sponsored listings. No manufacturer input. No paid placement on this page. Band thresholds and health messages are quoted from the publishing agencies; the AQHI-AQI mapping is labeled an approximation because no official conversion exists, and we say so rather than inventing one.
How this guide was researched
We compared the published AQHI and AQI methodologies and band definitions from ECCC, Health Canada, and EPA AirNow documentation, and validated the smoke-event alignment against how both agencies communicate PM2.5-driven events, including BC's hourly-PM2.5 smoke adjustment. Primary sources: Health Canada — Wildfire smoke, air quality and your health; Environment and Climate Change Canada — Air Quality Health Index; US EPA — AirNow air quality index and NowCast; Government of British Columbia — Air quality warnings; BlueSky Canada — FireSmoke.ca smoke forecast. Reviewed quarterly and on any change to the cited guidance or rulemaking.
We compared the published AQHI and AQI methodologies and band definitions from ECCC, Health Canada, and EPA AirNow documentation, and validated the smoke-event alignment against how both agencies communicate PM2.5-driven events, including BC's hourly-PM2.5 smoke adjustment. Primary sources: Health Canada — Wildfire smoke, air quality and your health; Environment and Climate Change Canada — Air Quality Health Index; US EPA — AirNow air quality index and NowCast; Government of British Columbia — Air quality warnings; BlueSky Canada — FireSmoke.ca smoke forecast. Reviewed quarterly and on any change to the cited guidance or rulemaking.
Disclosure
WC Safety participates in the Amazon Associates Program and earns from qualifying purchases via tagged links; WC Safety is not a retailer in this category. Neither relationship influences this guide. General information, not medical, legal, or regulatory advice — consult a Certified Industrial Hygienist or qualified safety professional for commercial programs.
WC Safety participates in the Amazon Associates Program and earns from qualifying purchases via tagged links; WC Safety is not a retailer in this category. Neither relationship influences this guide. General information, not medical, legal, or regulatory advice — consult a Certified Industrial Hygienist or qualified safety professional for commercial programs.
Related reference
Related reading in this area: how to choose a respirator cartridge: complete selection guide, best n95 mask for wildfire smoke, 3m 6000 vs 6500 vs 7500: same cartridges, three comfort tiers, best n95 respirator for construction 2026, best n95 respirator for welding 2026, and best papr respirator systems.
Why trust WC Safety
WC Safety is an independent, affiliate-supported review site. It is not a retailer: it holds no inventory, takes no orders, and earns only from qualifying purchases through clearly marked links — which never changes what a product is rated to do. Standards language is taken from the regulation text directly, and ratings are reported as the manufacturer publishes them. We run no laboratory and perform no testing of our own. Where published sources disagree, we say so and plan on the conservative figure rather than the flattering one.
Our methodology
Figures come from the regulation and the published specification, in that order. Derated numbers are calculated, not estimated. Nothing here is presented as a measured result, because we measure nothing.
Researched and written by Steven Eaton, editor of WC Safety. Steven holds no safety certification and does not test products; this page compares what manufacturers and regulators publish, with the gaps in that record marked. Last reviewed August 2026.
Frequently Asked Questions
Is Canada's AQHI the same as the US AQI?
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.
What is Why there is no exact conversion?
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.
What is worked example?
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:
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