Air Quality Health Index

The Air Quality Health Index (AQHI) is Canada’s public-health scale that communicates current and forecast health risk from air pollution. It is published by Environment and Climate Change Canada (ECCC) with provinces/territories and health partners. The AQHI runs from 1 to 10+, grouped into four risk categories—Low, Moderate, High, and Very High—with activity guidance for the general population and for at-risk individuals (e.g., people with heart or lung disease, children, older adults, and people who are pregnant).

At a glance — Air Quality Health Index (AQHI)

What it shows	Hourly health risk from outdoor air pollution and a short-term forecast (today/tonight/tomorrow)
Scale	1–3 Low • 4–6 Moderate • 7–10 High • 10+ Very High
Main drivers	Fine particles (PM2.5, incl. wildfire smoke) • Ground-level ozone (O₃) • Nitrogen dioxide (NO₂)
Where to check	weather.gc.ca (city pages) • provincial/territorial air sites • local media & municipal feeds

What the AQHI is (and isn’t)

The AQHI is a health-based index. It transforms near-real-time pollution measurements into a single number linked to short-term health risk messaging. It is not a pollutant standard and not a long-term air-quality grade for a city. Read it like a weather forecast for breathing conditions: values can change from hour to hour and vary block to block.

The AQHI scale and guidance

AQHI	Risk category	General population — guidance	At-risk population — guidance
1–3	Low	Ideal air quality for outdoor activities.	Same as general population; maintain usual activities.
4–6	Moderate	Most people can continue normal outdoor activities. If you experience symptoms (cough, throat irritation, shortness of breath), consider reducing or rescheduling strenuous activities.	Consider reducing or rescheduling strenuous activities outdoors, especially if symptoms occur; take more breaks and plan lower-intensity options.
7–10	High	Consider reducing or rescheduling strenuous activities outdoors if you experience symptoms. Keep an eye on vulnerable family members.	Reduce or reschedule strenuous activities; choose light activities and shorten time outdoors. People with heart/lung disease, children, older adults, and people who are pregnant should take extra care.
10+	Very High	Reduce or reschedule strenuous activities; if symptoms are strong or persist, move indoors to cleaner air.	Avoid strenuous activities outdoors; stay indoors in a clean-air space if possible. Follow your health-care provider’s plan; seek medical advice if symptoms are severe.

Common symptoms to watch for

Coughing, throat or sinus irritation, burning eyes, unusual fatigue, chest tightness, wheeze, or shortness of breath—especially during smoke or ozone episodes. People with asthma/COPD or heart disease may feel effects sooner and at lower AQHI values.

What goes into the AQHI

• Pollutants: fine particulate matter (PM2.5), ground-level ozone (O₃), and nitrogen dioxide (NO₂)—chosen because short-term changes in these pollutants are strongly linked to health outcomes.
• Data sources: urban and regional monitoring stations (hourly instruments) blended with quality control; forecasts use numerical models plus recent observations.
• Computation: a health-risk function from epidemiological studies converts concentrations into a 1–10+ scale. (Exact coefficients are technical and may differ by jurisdiction; the user only needs the risk categories and advice.)
• Updates: current conditions are typically refreshed hourly; forecasts provide today/tonight/tomorrow outlooks for each community.

Note on “AQHI-Plus” and wildfire variants: Some jurisdictions publish enhanced versions that emphasize PM2.5 during heavy smoke to better reflect health risk. The public guidance remains the same: follow the category advice above.

Wildfire smoke and AQHI

Wildfire smoke primarily raises PM2.5. When smoke is present:

• Prefer indoor spaces with cleaner air (HEPA air cleaners; well-sealed rooms).
• If you must be outdoors for extended periods, a well-fitted respirator (e.g., N95/KN95) can reduce inhalation of fine particles; surgical/cloth masks offer limited protection against smoke.
• Keep medications handy (e.g., asthma inhalers) and follow action plans.
• Check for Special Air Quality Statements or Smoky Skies Bulletins in addition to the AQHI.

Seasonal patterns (typical)

• Winter: wood-smoke and inversions can elevate PM2.5 in valleys and urban basins; cold, calm nights favour stagnation.
• Spring: wind-blown dust and early fires may raise particles in the Prairies/interior.
• Summer: ozone and wildfire smoke drive many High/Very High events, especially during heat waves or regional fire activity.
• Autumn: lingering smoke in fire-prone regions; occasional ozone spikes on warm, sunny days.

Regional notes

• Coast & mountains: terrain funnels winds and traps pollution under inversions; sea breezes can clear air by afternoon.
• Prairies & North: long transport can carry smoke thousands of kilometres; dust events occur in dry, windy conditions.
• Great Lakes & St. Lawrence: lake breezes and large urban areas shape ozone and particle patterns; humidity can worsen comfort during poor air days.
• Atlantic: marine fog is common but not an AQHI driver by itself; downwind transport from North America or Europe can affect episodes.

How to protect yourself (quick checklist)

• Check the AQHI and forecast for your community before outdoor plans.
• Adjust intensity and duration of outdoor exercise when AQHI is Moderate or higher—especially if you are at risk.
• Keep indoor air clean: close windows during smoke episodes; use HEPA air cleaners sized for the room (or an equivalent DIY filter box used safely).
• Use respirators (N95/KN95) correctly if you must be outdoors during High/Very High smoke.
• Look out for children, older adults, pregnant people, and anyone with chronic heart/lung conditions.
• Combine AQHI with heat alerts or cold warnings —multiple stressors can amplify health risks.

For schools, sports, and workplaces

• Establish thresholds (e.g., modify activities at 7–10, move indoors at 10+).
• Prefer low-intensity activities, shorten play/practice times, and increase rest/hydration during poor air days.
• Ensure indoor spaces used as refuges have adequate filtration and cooling during hot smoke events.

How AQHI compares internationally

Canada’s AQHI is a health-risk scale (1–10+) and differs from the U.S. AQI colour scale or Europe’s indices. Direct number-to-number comparisons are not meaningful; always follow the local guidance attached to your index.

Data access

Community pages on weather portals show current AQHI values, recent trends, and forecasts. Many provinces also publish maps, station details, and downloadable time series; national open-data portals provide program and model information.

See also

• Environment and Climate Change Canada • Weather in Canada • Public safety in Canada • Emergency management in Canada

External links (official)

• Air Quality Health Index — Public guidance & FAQs: https://www.canada.ca/en/environment-climate-change/services/air-quality-health-index.html
• Weather warnings, city forecasts & AQHI: https://weather.gc.ca/
• Historical climate & air resources: https://climate.weather.gc.ca/