A large-scale Saharan dust cloud is due to hit Spain, Italy and France on Tuesday, severely affecting air quality.
The Copernicus Atmosphere Monitoring Service (Cams) has been tracking the plume as it travels across the Mediterranean Sea.
Scientists say it will affect air quality in most of the western Mediterranean, especially Spain, where high particulate matter concentrations are predicted over much of the country, peaking on Tuesday.
The dust could also reach the islands of Corsica and Sardinia and affect south-eastern France and northern Italy, they added.
Spain is already contending with a heatwave, which like the dust cloud, has been driven by hot air from the Sahara, experts said.
Cams forecasts show a thick plume developing over the Canary Islands with hot, sand-laden winds later in the week.
Scientists have also identified dust in parts of the Caribbean.
“This episode of dust transport is coincident with the heatwave conditions experienced across Spain and the western Mediterranean related to the origins of the air mass over the Sahara," said Mark Parrington, senior scientist at Cams.
"In contrast with some of the episodes over the Mediterranean earlier in the year, our forecasts are showing higher concentrations of particulate matter at the surface, as well as higher up in the atmosphere.”
Cams monitors all stages of dust travelling from the Sahara and has been providing updates on the severity of this year's clouds.
A Cams report earlier this year revealed carbon emissions from last summer's wildfires in Europe were the highest in 15 years, with some countries recording their highest levels in 20 years. Spain was hit by nearly 500 wildfires that destroyed more than 300,000 hectares last summer.
The report also revealed temperatures were rising in Europe at twice the global average rate – faster than any other continent.
