Data & Converters
World Air Quality Index (AQI) Tracker
Live US AQI and PM2.5/PM10 readings for any city — know whether the air you breathe is safe, in real time.
Delhi — air quality
US AQI
154
Unhealthy
PM2.5
54.6 µg/m³
PM10
220.7 µg/m³
Live data from Open-Meteo air-quality models. US AQI scale: 0–50 Good, 51–100 Moderate, 101–150 Unhealthy for sensitive groups, 151+ Unhealthy.
Why air quality matters for health and travel
Air pollution is one of the world's largest environmental health risks, linked to respiratory disease, heart conditions and reduced life expectancy. For travellers, athletes and anyone with respiratory sensitivity, knowing the AQI at a destination is as important as knowing the weather — sometimes more.
A city might be sunny and pleasant yet have hazardous air during wildfire season, a dust event or a winter inversion. Checking AQI before you go — and during your stay — lets you adapt plans, pack a mask and avoid outdoor exertion on the worst days.
What AQI actually measures
An Air Quality Index rolls up several pollutants into a single number. The US AQI incorporates ground-level ozone, PM2.5, PM10, carbon monoxide, sulfur dioxide and nitrogen dioxide, reporting the dominant pollutant's value. This tool focuses on PM2.5 and PM10, the pollutants most consistently modelled globally and most relevant to everyday health.
The index is non-linear: a jump from 50 to 100 is not twice the pollution, because the bands reflect health thresholds rather than concentration. The colour bands communicate risk more intuitively than raw numbers.
PM2.5: the most dangerous pollutant
PM2.5 — particles under 2.5 microns, about 3% the width of a human hair — is the pollutant most strongly linked to premature death. Its small size lets it bypass the body's filters, passing from the lungs into the bloodstream and inflaming the cardiovascular system. Long-term PM2.5 exposure is associated with heart disease, lung cancer and cognitive decline.
PM2.5 comes from combustion (vehicles, power plants, wildfires, household heating), industrial processes, dust and chemical reactions in the atmosphere. Cities with heavy traffic, coal power or seasonal burning tend to have the highest readings.
Reading the colour bands
The US AQI scale runs 0–500+, colour-coded so you can judge risk at a glance. Green (0–50) is good — no precautions needed. Yellow (51–100) is moderate — unusually sensitive people may react. Orange (101–150) is unhealthy for sensitive groups — children, the elderly, and those with heart or lung disease should limit exertion. Red (151–200) is unhealthy for everyone.
Purple (201–300) is very unhealthy — everyone should avoid outdoor exertion. Maroon (301+) is hazardous, a public-health emergency. This tool colours the result by band so the risk is immediately visible.
Different AQI scales around the world
Several AQI systems exist and they are not interchangeable. The US AQI, used here, is the most internationally recognised. The European Common Air Quality Index (CAQI) uses different breakpoints. China's AQI is stricter on some pollutants. India's National AQI follows another scale. The same concentration can map to different numbers in different systems, so always compare like with like.
This tool uses the US AQI because it is widely understood and provides a consistent international yardstick. When you see an AQI number locally, check which scale it uses before comparing it to figures from home.
Protecting yourself when air is poor
When AQI rises above 100, sensitive groups should reduce prolonged outdoor exertion. Above 150, everyone benefits from limiting exertion, closing windows, and running a HEPA air purifier indoors. A well-fitted N95 or FFP2 mask substantially reduces PM2.5 exposure outdoors; cloth and surgical masks help far less.
Plan indoor alternatives on poor-air days, schedule runs and cycling for early morning when pollution is often lower, and avoid exercising near busy roads regardless of the city-wide AQI — local levels can be much higher in traffic canyons. For long stays in polluted cities, a home air purifier is one of the highest-value health investments you can make.
Frequently Asked Questions
What is the US AQI?
The US Air Quality Index converts pollutant concentrations into a 0–500+ scale where higher is worse. It is colour-coded: 0–50 Good, 51–100 Moderate, 101–150 Unhealthy for sensitive groups, 151–200 Unhealthy, 201–300 Very Unhealthy, 301+ Hazardous.
What are PM2.5 and PM10?
Particulate matter under 2.5 and 10 microns. PM2.5 is the more dangerous because it penetrates deep into the lungs and bloodstream. It comes from combustion (vehicles, power, wildfires), dust and secondary chemical formation.
Where does the data come from?
Live readings come from Open-Meteo's air-quality API, which combines satellite, ground-station and model data (including the Copernicus CAMS model). It updates multiple times per day.
Is AQI the same worldwide?
No. The US AQI, the European CAQI and China's AQI use different breakpoints, so the same PM2.5 value maps to different numbers. This tool uses the US AQI for international comparability.
What should I do when AQI is high?
Reduce outdoor exertion, keep windows closed, run an air purifier if available, and wear a well-fitted N95/FFP2 mask outdoors when AQI exceeds 150. Sensitive groups (asthma, heart disease, pregnancy, children, elderly) should minimise exposure above 100.
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