AQI Around the World: US vs EU vs UK vs Canada vs India

Last updated May 29, 2026 · 8 min read

If you travel internationally, you'll see air quality reported on different scales by different agencies. An AQI of 100 in Los Angeles means something different than an AQI of 100 in London, an AQHI of 5 in Toronto, or an AQI of 200 in Delhi. This guide compares the major systems, explains why they differ, and tells you what to look for when you're somewhere new.

The major systems, side by side

The U.S. EPA AQI

The system this site primarily covers. 0–500 scale, six categories (Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, Hazardous), color-coded green → maroon. Reports the worst of six pollutants (PM2.5, PM10, ozone, NO₂, SO₂, CO) — the "dominant pollutant." See Understanding AQI for the full mechanics.

The European AQI

The European Environment Agency publishes a 6-category index (Good, Fair, Moderate, Poor, Very Poor, Extremely Poor) based on five pollutants (PM2.5, PM10, ozone, NO₂, SO₂). The category breakpoints are looser at the bottom than the U.S. scale — what the U.S. calls "Moderate" generally maps to EU "Fair" or "Moderate." Europe also publishes a separate measurement-based view that reports raw concentrations.

A notable difference: European limit values (the actual regulatory standards, not just the index) have historically been more relaxed than U.S. NAAQS for PM2.5. In 2024 the EU approved a tightening to bring 2030 limit values closer to U.S. levels. Full breakdown: The European AQI Explained.

The UK Daily Air Quality Index (DAQI)

UK Defra publishes a simpler 1–10 scale with 4 bands (Low 1–3, Moderate 4–6, High 7–9, Very High 10). Each pollutant has its own breakpoints; the overall DAQI is the maximum across pollutants. The 1–10 scale maps roughly to:

• DAQI 1–3 ≈ U.S. AQI 0–50 (Good)
• DAQI 4–6 ≈ U.S. AQI 51–150 (Moderate to USG)
• DAQI 7–9 ≈ U.S. AQI 151–200 (Unhealthy)
• DAQI 10 ≈ U.S. AQI 200+ (Very Unhealthy and worse)

Full breakdown: The UK DAQI Explained.

Canada's Air Quality Health Index (AQHI)

Canada uses a different approach: an integrated health-risk index from 1 to 10 (with 10+ for extreme events) that combines PM2.5, NO₂, and ozone into a single number representing relative health risk, not pollutant concentration. Categories: Low risk (1–3), Moderate (4–6), High (7–10), Very High (10+).

Canada's system is more directly tied to mortality risk than the U.S. system, but in practice the action thresholds line up similarly: AQHI 4–6 ≈ U.S. orange; AQHI 7–10 ≈ U.S. red. Full breakdown: Canada's AQHI Explained.

India's National Air Quality Index

India's Central Pollution Control Board (CPCB) uses a 0–500 scale similar in structure to the U.S. system, with six categories (Good 0–50, Satisfactory 51–100, Moderate 101–200, Poor 201–300, Very Poor 301–400, Severe 401+). Note the categories don't line up with the U.S.: what the U.S. calls "Unhealthy" (151–200) is in India's "Moderate" band.

The reason for the different boundaries is partly that ambient PM2.5 in major Indian cities is multiples of typical U.S. urban concentrations. Indian residents adapted thresholds reflect the local population's baseline exposure. Full breakdown: India's National AQI Explained.

Singapore's Pollutant Standards Index (PSI)

Singapore's National Environment Agency reports a 0–500 PSI descended from the legacy U.S. EPA PSI, with five bands (Good, Moderate, Unhealthy, Very Unhealthy, Hazardous). Because Singapore's worst air comes from transboundary haze that can move fast, NEA also publishes a 1-hour PM2.5 reading alongside the 24-hour PSI — that's the number to watch during a haze episode. Full breakdown: Singapore's PSI Explained.

South Korea's Comprehensive Air-quality Index (CAI)

South Korea's CAI (on AirKorea) runs 0–500 but collapses into just four grades (Good, Moderate, Unhealthy, Very Unhealthy), and reports the gaseous pollutants in parts per million rather than µg/m³. The single wide "Unhealthy" grade (101–250) covers a lot of ground, so it's worth checking the underlying PM2.5 when it's orange. Full breakdown: South Korea's CAI Explained.

Australia's AQI

Australia takes a different approach entirely: each pollutant's AQI is its concentration as a percentage of the national standard, so 100 means "exactly at the standard." Category labels and cut-points vary by state and territory. Full breakdown: Australia's AQI Explained.

China AQI

China's system also uses 0–500 with six categories, broadly similar to the U.S. but with somewhat different breakpoints for individual pollutants. China publishes both the AQI and the IAQI (Individual Air Quality Index) for each pollutant so observers can see the dominant pollutant directly. See our China AQI guide for the breakpoints, or Beijing air quality.

Other national systems

Several more countries run their own indices, most sharing the "0–500, worst pollutant wins" structure but with locally tuned breakpoints:

• Hong Kong uses its own Air Quality Health Index (AQHI) — a 1–10+ health-risk scale (distinct from Canada's identically named index), reported separately for general and roadside stations. See the Hong Kong AQHI guide or Hong Kong air quality.
• Indonesia reports the ISPU (Indeks Standar Pencemar Udara), a 0–500 index with categories from Good to Hazardous. See Jakarta air quality.
• Thailand uses a 0–500 AQI similar in structure to the U.S. scale, published via Air4Thai. See Bangkok air quality.
• Pakistan reports an AQI close to the U.S./Indian model; Lahore's winter smog makes it one of the most-watched. See Lahore air quality.
• Mexico uses the IMECA-based Índice Aire y Salud, with a long history of ozone management in the capital. See Mexico City air quality.
• Japan reports against national environmental standards via the Ministry of the Environment's "Soramame" network rather than a single 0–500 number; summer photochemical-ozone advisories are the main alert. See our Japan air-quality standards guide or Tokyo air quality.
• The Philippines publishes a national AQI through its environment bureau (DENR-EMB). See Manila air quality.
• Bangladesh uses an AQI close to the U.S. model; Dhaka's winter particulate makes it one of the most-watched. See Dhaka air quality.
• Brazil's São Paulo state agency CETESB runs one of Latin America's most respected indices. See São Paulo air quality.

The WHO 2021 guidelines (not an index)

The World Health Organization publishes guideline values for each pollutant — recommended thresholds below which significant health effects are not documented. Not an index in the traditional sense, but the most aggressive set of values internationally. For PM2.5: 5 µg/m³ annual average, 15 µg/m³ 24-hour. Most countries' standards are well above WHO values; the WHO recommends them as long-term targets.

Why the indices disagree

Three reasons different countries report differently:

1. Different baselines. A "normal" day in a city averaging 50 µg/m³ PM2.5 looks different from a "normal" day in one averaging 10 µg/m³. Categories built for one don't translate cleanly to the other.
2. Different communication goals. The U.S. system tries to give a single number across pollutants. Canada's tries to communicate health risk directly. Europe's tries to balance simplicity with measurement transparency.
3. Different pollutant mixes. Some regions (Delhi, Beijing) are dominated by PM2.5; others (LA) historically by ozone. Index designs reflect what locals actually breathe.

Quick travel-comparison cheat sheet

• U.S. or Mexico: read the EPA-style AQI; 100 = action threshold for sensitive groups, 150 = action for all.
• Canada: AQHI 4–6 = exercise caution if sensitive, 7+ = limit outdoor effort.
• UK: DAQI 4+ = symptoms possible for sensitive people, 7+ = avoid outdoor exertion if affected.
• EU: "Poor" or worse = same actions as U.S. red.
• Singapore: watch the 1-hour PM2.5 reading during haze, not just the 24-hour PSI; PSI 101+ = ease off outdoor exertion.
• South Korea: the "Unhealthy" grade (101–250) is broad — check the underlying PM2.5 when it's orange.
• Australia: AQI 100 = at the national standard; under 67 is clean, 150+ is poor for everyone.
• India / China: the country systems are scaled to local baselines; consider also checking PM2.5 in µg/m³ directly — the WHO 24-hour guideline of 15 µg/m³ gives a stable benchmark across borders.
• Anywhere: when traveling, the most universal metric is raw PM2.5 concentration in µg/m³. WHO's 24-hour threshold (15 µg/m³) is the same everywhere on Earth.

The bottom line

A U.S. AQI of 100 and a Delhi AQI of 100 don't mean the same thing about the air — the underlying concentrations are very different — but they both mean "starting to be a problem for sensitive people" in their respective scales. The categorical interpretation generally translates; the numerical comparison doesn't. For meaningful cross-border comparison, look at raw PM2.5 concentration in µg/m³ alongside the local index.

Primary sources: EPA AirNow · EEA European AQI · UK Defra DAQI · Canada AQHI · India CPCB AQI