What is the AQI?
The Air Quality Index summarises with a single value (1 to 6) the worst pollution level measured at a station.
It is computed from the main regulated pollutants (PM2.5, PM10, NO₂, O₃, SO₂ and CO), taking the worst level at any moment. The scale is the one harmonised by Spain's Ministry for the Ecological Transition (MITECO) following European guidance.
Scale
Good
Air quality is good. No health risk — outdoor activities can be enjoyed normally.
Fair
Air quality is acceptable. Outdoor activities can be enjoyed normally.
Moderate
Consider reducing prolonged intense outdoor activity if you feel discomfort.
Poor
Reduce intense outdoor activity, especially near traffic.
Very poor
Avoid outdoor physical activity and limit non-essential travel.
Extremely poor
Stay indoors with windows closed. Minimise exposure to outdoor air.
For sensitive people: respiratory health guide and pollen forecast
A worked example
Imagine a station currently measuring two pollutants:
- NO₂: 60 µg/m³ → fair level (this level's threshold: ≤ 90 µg/m³)
- O₃: 120 µg/m³ → moderate level (this level's threshold: ≤ 130 µg/m³)
The worst pollutant wins: the station's AQI is Moderate and its dominant pollutant is O₃. That is the same “Dominant pollutant” label you will see on the map and on station pages.
Pollutants
Each pollutant has its own thresholds. The level shown on the map is always the worst among those available, and the dominant pollutant is shown.
PM2.5 (µg/m³)
- Good
- ≤ 10
- Fair
- ≤ 20
- Moderate
- ≤ 25
- Poor
- ≤ 50
- Very poor
- ≤ 75
PM10 (µg/m³)
- Good
- ≤ 20
- Fair
- ≤ 40
- Moderate
- ≤ 50
- Poor
- ≤ 100
- Very poor
- ≤ 150
NO₂ (µg/m³)
- Good
- ≤ 40
- Fair
- ≤ 90
- Moderate
- ≤ 120
- Poor
- ≤ 230
- Very poor
- ≤ 340
O₃ (µg/m³)
- Good
- ≤ 50
- Fair
- ≤ 100
- Moderate
- ≤ 130
- Poor
- ≤ 240
- Very poor
- ≤ 380
SO₂ (µg/m³)
- Good
- ≤ 100
- Fair
- ≤ 200
- Moderate
- ≤ 350
- Poor
- ≤ 500
- Very poor
- ≤ 750
CO (mg/m³)
- Good
- ≤ 5
- Fair
- ≤ 7.5
- Moderate
- ≤ 10
- Poor
- ≤ 20
- Very poor
- ≤ 30
What each pollutant measures
Not all pollutants behave the same way. Some are emitted directly by vehicles, ships, industry or fires, while others form in the atmosphere from those emissions. In the Canary Islands, Saharan dust and, in specific situations, volcanic context can also have a clear influence on some of them.
PM2.5
What it is
Very fine airborne particles with a diameter smaller than 2.5 micrometres. Because of their size they can penetrate deeper into the respiratory system.
Common sources
They usually come from combustion: road traffic, ships, power plants, heating, biomass burning and wildfires. They can also form in the air from other pollutant gases.
PM10
What it is
Airborne particles up to 10 micrometres in diameter. They include dust, ash, smoke and other solid or liquid particles present in the air.
Common sources
Common sources include traffic, construction, road dust resuspension, industrial activity and, in the Canary Islands, Saharan dust outbreaks, which can raise this pollutant sharply.
NO₂
What it is
Nitrogen dioxide is a gas generated mainly by high-temperature combustion processes.
Common sources
It is usually associated with road traffic, shipping, airports, power plants and other fuel-burning facilities. In urban areas it is one of the pollutants most closely linked to mobility.
O₃
What it is
Ground-level ozone is not usually emitted directly. It forms in the atmosphere when other pollutants react in sunlight.
Common sources
That is why it can increase on sunny, stable days, even far from the original emission source. Its main precursors are nitrogen oxides and certain volatile organic compounds from traffic, industry, ports or solvents.
SO₂
What it is
Sulphur dioxide is a gas released when sulphur-containing fuels are burned or in certain industrial activities.
Common sources
Its most common sources are some industrial processes, power plants, refineries and ships. In the Canary Islands it should also be interpreted carefully during episodes with a volcanic origin, when present.
CO
What it is
Carbon monoxide is a gas produced when combustion is incomplete.
Common sources
It usually comes from traffic, engines, machinery, open burning, wildfires and other fuel-using equipment. Outdoors it is more often linked to urban combustion or smoke episodes.
Data sources
We show data from the Government of the Canary Islands and datos.canarias.es. AQICN is only used as backup when the official source is unavailable.
Quick questions
Why do I see “no recent data”?
A signal is considered outdated once it goes more than 4 hours without a new reading. Instead of hiding the value, we keep showing the latest available reference with its date and time, flagged as “no recent data”.
Does Saharan dust count towards the AQI?
Yes, indirectly: suspended dust raises the PM10 particles measured by the stations, and that increase can worsen the AQI. Saharan dust is not pollen or an allergy alert, and its signal is also shown separately on the dust page.
How often is the data updated?
We check the official network every 10 minutes, although stations usually publish a new measurement roughly once an hour. That is why every value shows the time of its latest reading.