airpollen

Data sources

Last updated: April 2026

SILAM — Finnish Meteorological Institute

Pollen forecasts for European cities are provided by the SILAM (System for Integrated modeLling of Atmospheric coMposition) model, developed and operated by the Finnish Meteorological Institute (FMI).

  • Coverage: Europe (approx. 25°W–45°E, 30°N–72°N)
  • Forecast horizon: 5 days
  • Species modelled: Birch, Grass, Alder, Olive, Ragweed, Hazel, Mugwort
  • Index: POLI (Pollen Index) scale 1–5 — Very Low, Low, Moderate, High, Very High
  • Update frequency: Daily

Storage policy: The SILAM licence imposes no restriction on storing or processing forecast data. airpollen.com retains SILAM data in its database to build a historical pollen record for European cities.

Attribution: European pollen model · Finnish Meteorological Institute (SILAM)

Google Pollen API

Pollen forecasts for cities outside Europe are provided by the Google Pollen API, part of Google Maps Platform.

  • Coverage: Global (outside European SILAM domain)
  • Forecast horizon: 5 days
  • Types modelled: Tree, Grass, Weed — category scale (None, Very Low, Low, Moderate, High, Very High)
  • Update frequency: Daily

Storage policy: Google Maps Platform Terms of Service Table 17.3.1 permits caching of forecast values for up to 24 hours. airpollen.com does not store Google Pollen data in its database. Data is cached for up to 24 hours then discarded, and refreshed every 4 hours via a scheduled fetch.

Attribution: Source: Google Maps (required by ToS §17.2, displayed on all pages where Google Pollen data appears)

How we select a data source for each city

Each city is served by its highest-priority available source:

  1. European cities — SILAM is always the primary source. If SILAM data is available, Google Pollen data is not fetched or displayed for that city.
  2. European cities with no SILAM coverage — If SILAM returns no data for a specific location, the city is flagged for manual review. A city-level override can be set to permit Google Pollen as a fallback for that city only.
  3. Non-European cities — Google Pollen only. SILAM is not fetched.

Adding new data sources

Before any new data source is integrated, its licence and storage permissions are reviewed and documented here. A source is only written to the airpollen.com database if its terms explicitly permit storage and downstream use of forecast data.