Air Quality & Wildfire Smoke Guide
The Air Quality Index (AQI) is the number that tells you whether it's actually safe to be outside — and it can swing from Good to Unhealthy in a single day when wildfire smoke, seasonal haze or urban pollution moves in. This guide explains what the AQI means, which destinations see genuine air-quality spikes, and how to protect yourself and your home when it happens.
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What the Air Quality Index actually measures
The AQI is a standardised 0-500 scale published by air-quality agencies worldwide. Rather than reporting raw pollutant concentrations — which vary by chemical and are meaningless to most people — it converts the most dangerous pollutant of the moment (usually fine particulate matter, PM2.5, at 2.5 micrometres or smaller — about 3% the width of a human hair) into one comparable number. PM2.5 is small enough to lodge deep in the lungs and pass into the bloodstream, which is why it drives most real-world air-quality alerts, including wildfire smoke and seasonal haze.
| AQI | Category | What it means |
|---|---|---|
| 0-50 | Good | Air quality is satisfactory; little or no risk. |
| 51-100 | Moderate | Acceptable, but unusually sensitive individuals may notice effects. |
| 101-150 | Unhealthy for Sensitive Groups | Children, older adults, and anyone with asthma, COPD or heart disease should limit prolonged outdoor exertion. |
| 151-200 | Unhealthy | Everyone may begin to experience effects; sensitive groups more seriously. |
| 201-300 | Very Unhealthy | Health alert — risk of effects is increased for everyone. |
| 301+ | Hazardous | Health warning of emergency conditions — everyone is likely to be affected. |
Category thresholds and guidance follow the US EPA / AirNow.gov standard, used as the international reference scale by most national monitoring agencies.
How to check air quality before you travel
Because smoke and haze events can appear or clear within 24-48 hours, a reading from last week tells you almost nothing about tomorrow. Check a live monitor a few days out and again the morning you leave: AirNow.gov covers the US in detail and includes international stations, while IQAir gives real-time city-by-city readings worldwide. If you're heading somewhere on the destination lists below, it's worth bookmarking one of these for the days immediately before you fly.
Wildfire smoke: why it behaves differently to normal pollution
Wildfire smoke is almost entirely fine particulate matter, and it doesn't stay near the fire — smoke plumes routinely travel hundreds of miles from the actual burn, meaning a city can see hazardous AQI readings under a clear blue sky with no fire anywhere nearby. Smoke also settles overnight when the air is still, so AQI is often at its worst first thing in the morning even during an otherwise "clearing" event. Because of this, wildfire smoke episodes are one of the few pollution events where checking a live monitor genuinely beats trusting your eyes.
Protecting your indoor air
The US EPA's own guidance for wildfire smoke events centres on building a "clean room" — one space kept as free of smoke as possible with doors and windows shut. Their two recommended layers of defence:
- A portable HEPA air cleaner sized to the room, run continuously, ideally one that's certified not to produce ozone.
- A MERV-13-or-higher filter in a central HVAC system, if you have one, to filter air as it recirculates through the whole home.
Independent testing backs this up: HEPA filtration captures the large majority of PM2.5 particles, and well-sized purifiers start reducing indoor particle counts within minutes, reaching their fullest effect within a few hours of continuous running. The catch is sizing and duration — a purifier rated for a bedroom won't keep pace with an open-plan living room, and it needs to stay running for the length of the event, not just switched on when the smoke smell is strongest.
HEPA filtration for smoke, haze and everyday pollution
PuroAir HEPA air purifiers
True HEPA filtration built to handle wildfire smoke, seasonal haze and ordinary household pollution — sized for bedrooms up to large living spaces.
Shop PuroAir →How clean is "clean"? The WHO guideline
For context on just how strict a genuinely healthy target is: the World Health Organization's 2021 air quality guidelines set an annual average PM2.5 target of just 5 µg/m³, and a 24-hour target of 15 µg/m³ — both far stricter than the levels most national AQI "Good" categories are built around. Very few major cities meet the WHO annual target on a sustained basis, which is part of why background urban pollution (not just wildfire smoke) is worth taking seriously in its own right.
Destinations where air quality genuinely matters
Most of the 200 destinations on this site have air quality that's a non-issue most of the year. These three groups are the exceptions — real, well-documented patterns worth checking before you go, not a general scare about air pollution everywhere.
🔥 Wildfire-smoke-prone destinations
These sit in regions with an established wildfire season (North American West Coast, Australia) where smoke can affect air quality even far from any active fire.
🏙️ Destinations with elevated background pollution
Dense traffic, industry and geography (basin cities trap air more than coastal or hilltop ones) mean these destinations regularly see AQI readings in the Unhealthy for Sensitive Groups range or worse, independent of any single event.
🌫️ Seasonal haze destinations
Parts of Southeast Asia see a well-documented "burning season," typically in the dry months, when agricultural and land-clearing fires push PM2.5 sharply higher for days or weeks at a time.
Frequently Asked Questions
What does the Air Quality Index (AQI) actually measure?
The AQI is a standardised 0-500 scale that converts real pollutant concentrations — mainly fine particulate matter (PM2.5), coarse particulate matter (PM10), ground-level ozone, carbon monoxide, sulfur dioxide and nitrogen dioxide — into a single number so air quality can be compared day to day and city to city. Most air-quality emergencies, including wildfire smoke and seasonal haze, are driven overwhelmingly by PM2.5.
What AQI level is considered unsafe?
0-50 is Good, 51-100 is Moderate, 101-150 is Unhealthy for Sensitive Groups, 151-200 is Unhealthy, 201-300 is Very Unhealthy and 301+ is Hazardous. Sensitive groups — children, older adults, and anyone with asthma, COPD or heart disease — should start limiting prolonged outdoor exertion once the AQI passes 100; health agencies recommend everyone limit it once it passes 150.
How do I check air quality before I travel?
Check a live monitor such as AirNow.gov or IQAir for city-by-city readings a few days before you travel and again the morning you leave — wildfire smoke and haze events can appear or clear within 24-48 hours, so a reading from last week tells you very little about tomorrow.
Do HEPA air purifiers actually help with wildfire smoke?
Yes, when sized correctly for the room and run continuously. True HEPA filtration captures the vast majority of the fine particles that make up wildfire smoke and urban PM2.5, and the US EPA's own guidance on building a 'clean room' during a smoke event specifically recommends a portable air cleaner sized to the room — or a MERV-13-or-higher filter in a central HVAC system — as the primary defence, alongside keeping windows and doors closed.
Is it safe to exercise outdoors when air quality is poor?
Once the AQI reaches Unhealthy for Sensitive Groups (101-150), sensitive individuals should shorten or move workouts indoors. Once it reaches Unhealthy (151+), general guidance is to reduce prolonged or heavy outdoor exertion for everyone, and to avoid it altogether above 200.
Sources: US EPA / AirNow.gov (AQI categories and clean-room guidance), World Health Organization 2021 Global Air Quality Guidelines, and independent HEPA filtration testing. This guide is educational and doesn't replace a live AQI reading for your specific dates and location — always check AirNow.gov or IQAir before you travel.
Planning a trip to one of these destinations? Check the full destination index for month-by-month weather, or head to a specific Los Angeles, Delhi or Bangkok climate guide to see seasonal patterns alongside the temperature and rainfall data.
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Climate data sourced from Open-Meteo (open source, open data licence). Monthly averages calculated from 2020–2023 historical data. Weather can be unpredictable — always check a live forecast before travelling.