Sources and method
Everything on airhome comes from open European or Portuguese data. Nothing is scraped from a commercial site, nothing is bought, and nothing is fetched from a third party while you are reading a page — the data is ingested on a laptop and shipped with the site.
Measured — monitoring stations
19,038,066 validated hourly observations from 71 Portuguese stations, 2013 to 2026, for PM2.5, PM10, NO₂ and O₃, aggregated here into monthly and annual means.
Source: EEA Air Quality Download Service, datasets E1a (verified) and E2a (up to date, not yet verified). Station coordinates and classification: EEA pan-European metadata. Station names and municipalities: APA QualAr. Licence: EEA re-use policy, free re-use with acknowledgement; QualAr station register CC BY 4.0. Checked 2026-09-21.
Observations are kept only where the reporter marked them valid. A year is charted only if at least half its hours are valid. Five stations' coordinates disagreed between the EEA metadata and QualAr by more than 2 km; we use the QualAr coordinate, because QualAr also gives the street address.
Modelled — the 1 km maps
Annual European air quality maps at 1 km, produced by the European Topic Centre on Human health and the Environment for the EEA, for 2021 to 2024. We clipped them to Portugal: 138,997 cells in the window, of which 88,808 fall inside Portugal.
Source: EEA SDI datahub, one dataset per pollutant and year, EPSG:3035, 1000 m. Methodology reports on Zenodo (CC BY 4.0). Licence: EEA re-use policy. Checked 2026-09-21.
The ozone layer is not an annual mean. It is the 93.2nd percentile of the daily maximum 8-hour running mean, in µg/m³ — the indicator the EU target value of 120 µg/m³ is written against. We keep it out of the headline rating because ozone is systematically higher in the clean rural interior.
Madeira and the Azores lie outside the map domain entirely. Thirty municipalities therefore have no modelled value and no rating.
Industry, roads, boundaries, projects
Industry — European Industrial Emissions Portal (EEA), reporting year 2024, 324 Portuguese facilities with declared air releases, in kg/yr as reported by the operator. Carbon dioxide is held separately and excluded from the local-air ranking.
Roads — OpenStreetMap ways tagged motorway, trunk or primary, 86,895 ways and about 25,500 km. © OpenStreetMap contributors, ODbL.
Boundaries — CAOP (Carta Administrativa Oficial de Portugal) 2024.1 from DGT, republished as GeoJSON by geoapi.pt: all 308 concelhos, plus 332 freguesias covering the 35 municipalities of the Lisbon and Porto metropolitan areas. Simplified to about 100 m.
Known projects — curated by hand, every entry with a citation to a government decision, an environmental impact file or reporting of one. It is a list, not a forecast; we do not estimate how much anything would change the air.
Address lookup — OpenStreetMap Nominatim, results cached so the same street is not looked up twice.
What airhome cannot tell you
- Whether an address is safe. We quote the WHO guidelines and the EU limit values and say who set them. We do not convert them into advice.
- What the air is doing today. Everything here is annual.
- Anything at street scale. A 1 km cell averages a square kilometre; nitrogen dioxide can halve within 200 m of a road.
- Indoor air, which for most people matters more than outdoor air and is driven by heating, cooking and ventilation.
- Wood smoke, which is a large winter source in much of rural Portugal and is only partly visible in annual means.
- What is planned near a specific house. Ask the câmara municipal.
Sources and what they cannot tell you
- Measured history — European Environment Agency Air Quality Download Service: 19,038,066 validated hourly observations from Portugal's 71 stations, 2013–2026. Station names from APA QualAr. A station is not your street. Nitrogen dioxide in particular varies by hundreds of per cent over a few hundred metres.
- Modelled values at the address — the EEA / ETC-HE 1 km European air quality maps, 2024 and the three years before it. A 1 km cell is an average over a square kilometre. It cannot see one side of a street being busier than the other, and it will understate a very local source and overstate a very local clean spot.
- Industry — European Industrial Emissions Portal, reporting year 2024, as declared by operators. Only installations above the European reporting thresholds appear. Emissions reported are annual totals: they say nothing about when, or which way the wind was blowing.
- Roads — OpenStreetMap, © OpenStreetMap contributors (ODbL). Distance to a road class, not to traffic. A quiet primary road and a jammed one look identical here.
- Boundaries — CAOP (Carta Administrativa Oficial de Portugal, DGT), all 308 concelhos and the freguesias of the Lisbon and Porto metropolitan areas.
- Known projects — curated by hand, each with a citation. Not a forecast. Incomplete by construction.
- Address lookup — OpenStreetMap Nominatim. A geocoder returns the coordinate it thinks you meant. Check the place name we echo back before trusting the figures.
- Not used — CAMS reanalysis, which would give hourly modelled history, needs a Copernicus Atmosphere Data Store key that this build does not have. Madeira and the Azores fall outside the 1 km European map domain, so those 30 municipalities have measured station data but no modelled values and no rating.
Data built 2026-09-21. airhome is free and has no commercial relationship with anyone selling property.