The five pollutants

The European Air Quality Index is built from five pollutants. A location takes the band of whichever one is worst, so the number you see is only ever as good as the worst thing in the air.

Why five, and why the worst one wins

The index does not average the five pollutants. It measures each one, assigns each its own band, and reports the worst. That is a deliberate design choice: averaging would let a genuinely bad ozone afternoon be cancelled out by clean particles, and the point of a public index is to describe the thing that might affect you.

The practical consequence is that the band on the front page is a statement about one pollutant at a time, and which one it is changes through the day and through the year. Nitrogen dioxide tends to set it in the morning rush beside a road; ozone on a hot still afternoon inland; coarse particles during a dust episode, at every station at once.

Each pollutant also has its own band boundaries. They are not a common scale, and reading one pollutant's number against another's thresholds is the most common way to misread this index — which is what the table below is for.

The same number means different things

These are the inclusive upper bounds of each band, in µg/m³, for each of the five pollutants. Read down a column and the scales diverge sharply: the ceiling of “Good” is 5 for fine particles and 60 for ozone — a twelve-fold difference in what counts as unremarkable air.

Inclusive upper bound of each index band, per pollutant, in micrograms per cubic metre
Band	PM2.5	PM10	NO₂	O₃	SO₂
Good	5	15	10	60	20
Fair	15	45	25	100	40
Moderate	50	120	60	120	125
Poor	90	195	100	160	190
Very poor	140	270	150	180	275
Extremely poor	800	1200	1000	600	1000

Source: European Air Quality Index (EEA), verified 2026-07-26. Each figure is the inclusive top of that band; a concentration is rounded to the nearest whole µg/m³ before it is matched.

One page each

Each guide covers what the pollutant is, where it comes from on these islands specifically, what it does to the people most affected by it, its own band scale, the legal limits and WHO guidelines that apply to it, and which of the 5 stations measure it.

PM2.5Fine particulate matter5 of 5 stationsFine particles are the pollutant with the clearest long-term health evidence behind it, and the one where Malta’s own number is usually unremarkable while the yearly average still matters.PM10Coarse particulate matter5 of 5 stationsCoarse particles are the pollutant Malta’s geography affects most: sea salt and Saharan dust both land in this figure, which is why a high PM10 hour here often has nothing to do with traffic.NO₂Nitrogen dioxide5 of 5 stationsNitrogen dioxide is the most local of the five: it is made by engines, it falls away within tens of metres of a road, and which station you look at matters more than for anything else.O₃Ozone4 of 5 stationsOzone is the one pollutant nobody emits. It is built in the air by sunlight, which is why it peaks on hot afternoons, is often worse in the countryside than in town, and is the pollutant Malta’s climate most reliably produces.SO₂Sulphur dioxide4 of 5 stationsSulphur dioxide is normally the quietest of the five in Malta — low for long stretches, then briefly not. It is the pollutant where an episode means more than an average.

Why five, and why the worst one wins

The same number means different things

One page each

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