A historic intrusion of Saharan dust, caused by squall Celia, is affecting the Iberian Peninsula. The particles, which come from the Sahara desert and travel across Europe to the tropical Atlantic, can degrade vision, cause respiratory problems and worsen air quality, making Spain now the country with the worst air pollution index in the world.

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Calima represents a fairly dry air mass with a high concentration of sand that is created over the Sahara, in the north of Africa. This desert releases around 800 million tonnes of dust per year, which accounts for 70% of the world’s dust emissions.

This morning Spain became the “most polluted” country in the world by Saharan particles, which come from nature but are still harmful to health.

The Celia squall is causing an episode of wind, rain and even snow at high altitudes in the interior of the peninsula. It has also caused significant waves on the Mediterranean coast and in the Canary Islands, but the most striking phenomenon is undoubtedly the invasion of Saharan air laden with suspended dust that is advancing across the peninsula.

Spain has become the “most polluted” country in the world by Saharan particles, which come from nature but are still harmful to health.

Cities such as Avila, Salamanca, Segovia and Madrid had concentrations of particulate matter below 10 micrometres (PM10) close to 1,000 micrograms per cubic metre (µg/m3). These figures become relevant if we compare them with the daily average that the World Health Organisation (WHO) considers to be healthy of 45 µg/m3. These figures are higher than those observed in China or India.

All this dust is being injected by Celia, which blows air from the North African desert, creating large columns of haze over the Iberian Peninsula and the Balearic Islands. Today, the haze is expected to reach most of Spain, except for the Canary Islands. This irruption will remain noticeable for the rest of the week, producing, in addition, mud showers.

At the same time as squall Celia hits Spain, a high pressure system will transport another huge cloud of dust from the Sahara to the tropical Atlantic. This anticyclone has higher pressure than usual, which gives it more strength and pushes stronger trade winds, creating a westward push of dust from Africa.

Calima also has positive effects, such as reducing the likelihood of tropical storms and being a natural fertiliser for oceans and soils.

Airborne dust particles significantly affect air quality, impair vision, create eye irritation and can cause respiratory problems. However, haze also has positive effects.

Among other things, it reduces the likelihood of tropical storms and is a natural fertiliser for oceans and soils. In addition, they reflect sunlight, thus cooling the atmosphere and reducing the warming of the ocean surface.