App Guide · Updated March 2024
Best AQI Apps 2024: IQAir vs WAQI vs PurpleAir vs AirNow — Which is Most Accurate?
We tested 6 major air quality apps on data accuracy, coverage, update speed, and usability. The right app depends on where you live and what you need.
Quick Answer
🌍 Best overall (global travel): IQAir AirVisual — best coverage + 72hr forecasts
🏛️ Most accurate (government data): WAQI — official monitors only, no low-cost sensors
🇺🇸 Best for USA: AirNow (EPA) — the official government standard
📍 Best hyperlocal (US cities): PurpleAir — but use EPA correction during wildfires
🇮🇳 Best for India: CPCB Sameer — official government monitoring network
Why Do Different AQI Apps Show Different Readings?
The most common question from users: "My IQAir says AQI 85 but WAQI says 120 — which is right?" The answer is usually: both are giving you accurate information from different sources, and the real value is somewhere in between.
🏛️
Official Government Monitors
Federal Reference Method instruments — gravimetric PM2.5 samplers or beta attenuation monitors. Gold standard accuracy. Updated hourly. Often sparse (1 per 50–200 km² in cities). Used by: WAQI, AirNow.
📡
Low-Cost Optical Sensors
Laser particle counters (e.g., PMS5003, SDS011). High density — thousands per city. Real-time (1-2 min). Affected by humidity, temperature, and particle type. Need calibration. Used by: PurpleAir, IQAir (partially).
🛰️
Satellite Data
NASA MODIS, Sentinel-5P, MERRA-2 reanalysis. Fills gaps in areas with no ground monitors. Accuracy ±30–50% for PM2.5. Updated daily. Used by: Plume Labs, IQAir (gap-filling), Google Air Quality.
🧮
Interpolation & Modeling
Apps estimate values between monitoring stations using kriging, ML models, or weather-based dispersion models. Can introduce errors in complex terrain or near industrial point sources.
App-by-App Comparison
IQAir AirVisual
iOS, Android, Web
9/10
Free
Best overall for travel + global coverage
Coverage
Global
Update Frequency
Real-time (1 min)
Data Sources
Government + low-cost sensors
Pros
- ✓ Most complete global city coverage
- ✓ Excellent forecast (72-hr AQICN model)
- ✓ Clean UI
- ✓ Apple Watch + widgets
Cons
- ✗ Low-cost sensor data can be inconsistent
- ✗ Premium weather features expensive
WAQI (World Air Quality Index)
iOS, Android, Web
8.5/10
Free
Most reliable — government-only data
Coverage
Global
Update Frequency
Hourly
Data Sources
Official government only
Pros
- ✓ Government-certified data only (no low-cost sensors)
- ✓ Longest historical archive
- ✓ Transparent data sourcing
- ✓ Free API available
Cons
- ✗ Sparse in developing nations
- ✗ Less polished UI
- ✗ Hourly updates only
PurpleAir
Web, iOS, Android
7.5/10
Free
Hyperlocal readings in covered areas
Coverage
USA + dense urban global
Update Frequency
Real-time (2 min)
Data Sources
Citizen science low-cost sensors
Pros
- ✓ Highest density in US urban areas
- ✓ Real-time neighborhood-level data
- ✓ Good wildfire coverage (Western US)
- ✓ Community-sourced
Cons
- ✗ Overestimates during wildfire smoke (EPA correction needed)
- ✗ Sparse outside US
- ✗ Sensor quality variable
AirNow (EPA)
iOS, Android, Web
8/10
Free
USA residents — most authoritative US data
Coverage
USA only
Update Frequency
Hourly
Data Sources
Official US EPA monitoring
Pros
- ✓ Official US government data
- ✓ Reliable and authoritative for US
- ✓ Good alert system
- ✓ Fire & Smoke Map integration
Cons
- ✗ US only
- ✗ Limited coverage in rural areas
- ✗ No international data
Plume Labs (Flow)
iOS, Android
7/10
Free
Personal exposure tracking with Flow sensor
Coverage
Global (sparse)
Update Frequency
Real-time + personal sensor
Data Sources
Satellite + government + personal device
Pros
- ✓ Personal sensor integration
- ✓ Personal exposure calculation
- ✓ Good satellite-derived data for sparse areas
Cons
- ✗ Sensor required for best accuracy
- ✗ Limited free coverage
- ✗ Less city coverage
India CPCB Sameer
iOS, Android
7.5/10
Free
India residents — authoritative national data
Coverage
India only
Update Frequency
Hourly
Data Sources
Official CPCB monitoring network
Pros
- ✓ Official India CPCB data
- ✓ City-level AQI + station maps
- ✓ AQI bulletin notifications
- ✓ Historical data access
Cons
- ✗ India only
- ✗ Older UI
- ✗ Some stations offline periodically
Summary Comparison Table
| App | Score | Best For | Price |
|---|---|---|---|
| IQAir AirVisual | 9/10 | travel + global coverage | Free |
| WAQI (World Air Quality Index) | 8.5/10 | Most reliable — government-only data | Free |
| PurpleAir | 7.5/10 | Hyperlocal readings in covered areas | Free |
| AirNow (EPA) | 8/10 | USA residents — most authoritative US data | Free |
| Plume Labs (Flow) | 7/10 | Personal exposure tracking with Flow sensor | Free |
| India CPCB Sameer | 7.5/10 | India residents — authoritative national data | Free |
⚠️ Special Case: Wildfire Smoke
During wildfires, PurpleAir sensors overestimate PM2.5 by 20–60% because wood smoke particles scatter laser light differently. The EPA developed the "AQI U-factor" correction. For accurate wildfire readings: use fire.airnow.gov (EPA Fire & Smoke Map) which applies this correction, or look for apps that explicitly state they apply EPA wildfire corrections. Never use uncorrected PurpleAir during active wildfire events.
Frequently Asked Questions
Which AQI app is most accurate?
IQAir AirVisual for global coverage. WAQI for government-only certified data. AirNow (EPA) for USA. PurpleAir for US hyperlocal (with EPA wildfire correction).
Why do different AQI apps show different readings?
Different data sources (government monitors vs low-cost sensors), different interpolation algorithms, different calibration methods, and different update frequencies. Government monitors are most accurate but less dense.
Is PurpleAir accurate during wildfire smoke?
No — PurpleAir overestimates by 20–60% during wildfires. Use EPA's Fire & Smoke Map (fire.airnow.gov) which applies the EPA wildfire correction factor to PurpleAir data.
Which AQI app works best in India?
CPCB Sameer app for official government data. IQAir AirVisual for mix of government + third-party with good coverage of Indian cities.
What AQI app is best for international travel?
IQAir AirVisual — best global city coverage, 72-hour forecasts, and clean UI for checking air quality before and during trips.