Saharan dust and Malta’s air

Dust lifted from North Africa recurs over the central Mediterranean through the year, and Malta sits directly on the corridor between the Sahara and southern Europe. An intrusion is a feature of the islands’ climate rather than an exceptional event, and it is the regional source behind most of the highest coarse-particle readings on this site.

What a dust intrusion actually is

Strong winds over the Sahara lift fine mineral material — clay, quartz, iron oxides — high enough into the atmosphere to be carried for thousands of kilometres. When the circulation over the Mediterranean is in the right configuration, that dust-laden air moves north across the sea and over the islands between North Africa and southern Europe. Malta is one of those islands, and it is close to the middle of the main track.

The dust arrives as an air mass rather than as a plume from a point source. That is the single most important fact about it for anyone reading a monitor, and almost everything else on this page follows from it: an air mass sits over the whole of Malta and Gozo at once, so it raises every station together.

Desert dust is predominantly coarse. It registers most strongly in PM10 — particles up to 10 micrometres — and much less in PM2.5. Both rise, but not equally, and the ratio between them is part of how an intrusion is recognised.

What it does to the readings

The effect is large. The PM10 band scale has “Good” ending at 15 µg/m³ and “Moderate” running up to 120, and its top band reaches 1200 — a ceiling that exists for dust events, not for anything urban traffic produces. During a significant intrusion the coarse-particle figure can move several bands in a few hours.

What it does not do is change what the measurement means. A microgram of mineral dust in your lungs is not meaningfully gentler than a microgram of brake dust. The particles are natural in origin and they affect the airways in much the same way as any other coarse particulate matter, which is why this site reports the band exactly as measured during an episode rather than discounting it.

Dust is context, never a measurement. It may explain an elevated PM10 reading; it never contributes to one. Every station's band comes from that station's own measured concentration and nothing else — no model value is ever mixed into, compared against, or substituted for a measurement.

How to recognise one from the readings

You do not need a forecast to spot a dust episode. The signature is in the pattern across stations, and once you know it you can read it off the front page.

Every station rises together: Raised coarse particles across several stations at once often indicate Saharan dust. Local traffic cannot do this. A roadside source raises the Traffic stations and leaves the Background ones comparatively alone; an air mass raises all five.
The rural station rises too: Għarb, on Gozo, is the network's only Rural-Regional site and the closest thing to a baseline for the islands. Elevated coarse particles there, as high as at the urban sites, is the clearest single indication that the cause is regional rather than local.
Coarse rises much more than fine: PM10 climbing sharply while PM2.5 climbs modestly points at mineral dust. A combustion event — smoke, heavy traffic, burning — tends to do the opposite, because burning makes fine particles and abrasion makes coarse ones.
It lasts a day or two, not a season: An intrusion is an air mass passing over. It builds, peaks and clears on a timescale of hours to a couple of days, which is quite unlike the slow seasonal rise and fall of ozone.

Where the dust forecast on this site comes from

Alongside the measurements, this site shows a modelled dust forecast so an elevated reading can be put in context before it happens. It comes from the Copernicus Atmosphere Monitoring Service, reached through the Open-Meteo Air Quality API, and it is a modelling system rather than a measurement network.

That distinction is load-bearing and this site is strict about it. The forecast is always labelled as modelled, always names CAMS, and always shows when it was retrieved. It is never presented as an observation, and it never adjusts a measured value.

When this site says there is dust

The judgement is deterministic rather than editorial, and the thresholds are the ones the classifier actually applies:

Modelled dust at or above 20 µg/m³ sustained for at least 3 hours raises a dust forecast at all. A single model hour is noise, not an episode.
At or above 50 µg/m³ it is reported as significant rather than routine.
If the dust field is missing, the panel is omitted rather than showing zero — the same rule the measurements follow.

Dust transport is one of the harder things atmospheric models get right. The figure is directional rather than precise, and the wording on the card is hedged on purpose: elevated modelled dust can raise coarse particles. It is never stated as the cause of a particular reading.

“It was only dust”

This phrase deserves its own section, because it is simultaneously a real phenomenon and a convenient excuse — and the two are easy to confuse deliberately.

The real part: dust is a natural source, Malta cannot prevent it, and an exceedance driven by a documented intrusion is genuinely not evidence of a local failure. European air quality law recognises this, and allows Member States to account for exceedances attributable to natural sources separately when assessing compliance.

The excuse part: none of that changes what you breathed. The health effect of a coarse particle does not depend on whether it came from the Sahara or from a quarry, and an episode attributed to dust is still a day on which strenuous outdoor exercise was a worse idea than usual. “Natural” is a statement about provenance and compliance accounting, not about your lungs.

It is also only sometimes true. A high coarse-particle reading can be dust, a dry windy day lifting local material, or genuinely dirty local air — and the three are distinguishable from the pattern across stations, which is why the pattern is worth learning rather than taking an attribution on trust.

What to do during an episode

The sensible response is the ordinary one for a bad-air day, and none of it requires knowing the number to a microgram.

Reduce strenuous outdoor exertion while levels are high — this matters most for people with asthma or other respiratory conditions, for whom coarse particles are a known trigger.
Keep windows shut on the windward side while the episode passes. Dust intrusions are short, so this is a measure for a day, not a season.
If you have asthma, have reliever medication to hand. Coarse-particle effects tend to be upper-airway and fast-onset rather than slow.
Check whether the rise is dust before concluding anything about local air quality — or about a local improvement, once it clears.

maqua.app provides general environmental information and does not replace medical advice or official emergency guidance.