AQI Forecast: Tomorrow's Air Quality & How Predictions Work
Last updated: December 2024
Quick Answer: Where to Get Your Forecast
- USA: AirNow.gov — official EPA next-day forecast
- Europe: Copernicus CAMS — 4-day EU forecast
- India: SAFAR India — Delhi, Mumbai, Pune, Ahmedabad
- Global: IQAir — 7-day forecast for thousands of cities worldwide
How AQI Forecasting Works
Air quality forecasting is one of the harder problems in environmental science. Unlike temperature or rain, AQI is influenced by both meteorology (which forecasters understand well) and emission chemistry (which is far less predictable).
The process works in three stages:
- Weather modeling: Numerical weather prediction models (NWS GFS, ECMWF) forecast temperature, wind, precipitation, and atmospheric stability. These determine how far pollutants will travel and whether inversions will trap them.
- Emission inventory: Known sources (roads, power plants, farms, ports) are mapped as hourly emission rates. Fire satellite data from NASA FIRMS adds wildfire and agricultural burning inputs dynamically.
- Chemical transport modeling: Systems like EPA's CMAQ, European SILAM, or ECMWF-CAMS simulate how pollutants react, disperse, and deposit. Secondary particle formation (ammonia + NOx → ammonium nitrate) is a critical chemical step.
The output is a grid of predicted PM2.5, ozone, and other pollutant concentrations, converted to AQI. For US cities, forecasters also apply human meteorologist judgment — the official AirNow forecast is issued by trained air quality meteorologists who adjust model output based on local knowledge.
Best AQI Forecast Sources by Region
Official US EPA forecasting for 300+ metropolitan areas. Provides next-day AQI forecasts for PM2.5, ozone, and PM10 based on NWS meteorological models.
airnow.gov ↗Aggregates station data globally. Some cities have forecast data. Provides maps and mobile app with push alerts when AQI exceeds thresholds.
waqi.info ↗Commercial platform with AQI forecasts for thousands of cities. Uses satellite data + surface stations + machine learning. Provides 7-day outlooks.
iqair.com ↗EU Copernicus Atmosphere Monitoring Service. High-resolution European forecasts for PM2.5, ozone, NO2. 4-day ahead. Uses ensemble of 7 European chemistry transport models.
atmosphere.copernicus.eu ↗India's System of Air Quality and Weather Forecasting. Covers Delhi, Mumbai, Pune, Ahmedabad. 3-day AQI forecasts with color-coded alerts.
safar.tropmet.res.in ↗Mobile-first AQI app with personal exposure tracking and forecasting. Uses hyperlocal modeling. Good for personal exposure minimization planning.
plumelabs.com ↗Forecast Limitations to Know
Fire smoke is nearly impossible to forecast more than 24–48 hours ahead. Even within that window, smoke plume modeling has large uncertainties in height, direction, and concentration.
A single AQI forecast for 'a city' can mask 50+ point differences between neighborhoods. Street canyons, proximity to roads, and park coverage create micro-climates no city-scale model captures.
Temperature inversions can form hours earlier or later than predicted, dramatically changing whether pollution accumulates. This is the main error source for highly polluted cities in winter.
Forecasts for cities in Africa, South Asia, and parts of Southeast Asia have higher uncertainty because there are fewer surface monitoring stations to validate and correct model outputs.
Frequently Asked Questions
How accurate are AQI forecasts?
Next-day AQI forecasts for well-monitored cities (US, Europe) are reasonably accurate — within 1 AQI category ~75–80% of the time. Accuracy degrades significantly beyond 3 days. For cities in South Asia, Southeast Asia, and Africa with sparse monitoring networks, forecast accuracy is considerably lower. Episode events like wildfire smoke can override models entirely with short notice.
How is an AQI forecast made?
AQI forecasts combine numerical weather prediction (wind, temperature, humidity, rain) with atmospheric chemistry models that simulate how emissions disperse, transform, and deposit. Inputs include traffic and industrial emission inventories, fire hotspot satellite data, and dust transport models. Major systems used: EPA's CMAQ, European SILAM/EMEP ensemble, ECMWF-CAMS. Machine learning corrections are increasingly applied on top of physics models.
Where can I get tomorrow's air quality forecast for my city?
For US cities: AirNow.gov provides official next-day forecasts. For European cities: Copernicus CAMS or national agencies (UK DAQI, French Atmo, German UBA). For Indian cities: SAFAR India covers major metros. Globally: IQAir and WAQI provide forecast tabs for many cities. All are free to use.
Can I get AQI forecast notifications?
Yes. AirNow (US) offers email/SMS alerts when next-day AQI is forecast above a threshold. IQAir and WAQI mobile apps offer push notifications. The EPA's EnviroFlash service sends forecasts to email subscribers for US cities.
Why does tomorrow's forecast sometimes differ from what actually happens?
AQI forecasts fail primarily due to: unexpected wind shifts, rain timing errors, unforecast wildfire or agricultural burning events, and temperature inversion formation/breakup timing. Urban AQI is also hyper-local — a single forecast can mask 50-AQI differences between neighborhoods separated by 2 km.