How Air Quality Is Calculated
WFY24 air-quality pages are based on Copernicus CAMS pollutant forecasts and presented through the European AQI scale used across the product.
Actual data flow for AQI pages
The AQI page follows the real product flow, but is described here at trust-page level rather than internal implementation level.
/{locale}/aqi/{city}
The canonical AQI page starts from a place slug, not from raw coordinates.
Canonical place resolution
The page resolves the place first to get coordinates, country code and localized place labels.
Initial AQI forecast
The server preloads the initial AQI forecast so the page opens in a stable way without visual jumps.
Background refresh layer
After the initial render, the AQI view can refresh in the background so it stays aligned with newer data.
European AQI + pollutant view
The page shows the aggregate AQI together with PM2.5, PM10, O3, NO2, SO2 and CO.
The public logic is simple: stable initial render first, controlled refreshes afterwards.
Technical facts already documented in the product
This strip only uses facts that already exist in the `/data-sources` page and AQI UI strings of WFY24.
1. Source data and cadence
WFY24 uses air-quality forecast data from the Copernicus Atmosphere Monitoring Service (CAMS), operated by ECMWF. In the existing data-sources documentation, CAMS is described as a 0.4° global grid with hourly forecasts for the next 5 days.
WFY24 documents that CAMS updates twice daily, at 00Z and 12Z. That means AQI pages should be read as forecast guidance that refreshes on a different cadence from the main weather model stack.
2. Pollutants included
WFY24 surfaces the same pollutant set documented in the product today: PM2.5, PM10, O₃, NO₂, SO₂ and CO.
- PM2.5 and PM10 reflect fine and coarse particulate pollution.
- O₃, NO₂, SO₂ and CO cover the main gas pollutants exposed in the CAMS feed.
- The result is displayed in a single air-quality view so users can compare hours quickly without parsing multiple pollutant charts first.
3. AQI framework used on WFY24
WFY24 states that it uses the European AQI method. On the site, that scale is presented as a 0-to-100+ range and mapped into human-readable categories such as Good, Fair, Moderate, Poor, Very Poor and Hazardous.
The purpose of the displayed AQI is not to hide pollutant detail, but to summarize forecast pollution stress into a comparable index while still exposing the underlying pollutant names and explanations on the page.
4. What AQI can and cannot tell you
AQI on WFY24 is forecast-based, not a direct street-corner sensor reading. Local traffic, wildfires, dust outbreaks, industrial plumes and sharp urban gradients can shift real conditions faster than a gridded model can fully capture.
For sensitive groups or official public-health guidance, national or city-level air-quality authorities should always take precedence over a general forecast view.