Skies in some parts of Spain have turned orange due to dust from the Sahara desert blowing in from across the Mediterranean.
People have been warned not to stay outside for long periods of time and advised to wear face masks due to extremely poor air ratings.
BBC weather forecasters warned that the dust clouds could move up into southern parts of England by Wednesday 16 March.
Here we take a look at how the dust storm formed and whether it will hit the UK.
What is the Sahara desert dust storm?
Storm Celia brought dust from the desert to southern parts of Spain, with Madrid and Murcia among the places affected.
Sand and dust storms occur annually when powerful, hot winds sweep across loose soils on arid land.
It is very harmful to human health, however the dust clouds do bring nutrient-laden minerals from the Sahara, the planet’s largest and hottest desert, to ocean life and vegetation.
Spain currently has the most unfavourable air quality globally, surpassing China and India where smog is notoriously bad, The Climatology Laboratory at the University of Alicante posted to Facebook on Tuesday (15March).
Where is currently being impacted?
Spain’s capital Madrid, along with resort towns in the south-east, are bearing the brunt of the dust that is being brought in from the Mediterranean.
Areas as far west as the Canary Islands in the Atlantic and the Balearic Islands in the Mediterranean are also being impacted.
A cloud of dust has also covered parts of Switzerland, replacing its normal blue sky with an unusual orange-brown hue.
Will it hit the UK?
BBC weather presenter Carol Kirkwood said the poor air quality could be felt in Britain as soon as Wednesday (16March).
"There has been very poor air quality today in parts of Spain, and it could well affect us in the southeast and East Anglia on Wednesday," she said.
What are the risks of Saharan desert dust?
Saharan desert dust poses risks to human health particularly those who suffer with asthma.
Dr Andy Whittamore, the clinical lead at Asthma UK, has previously warned of the risks posed by Saharan dust.
He said: "Toxic air can leave people struggling for breath and can cause wheezing, coughing, shortness of breath and even a life-threatening asthma attack.
“Saharan dust could pose a serious risk to the 5.4 million people in the UK with asthma.”
He added: "Dust and other types of air pollution are a well-known trigger for people with asthma.
“People with asthma must make sure they carry their reliever inhaler (usually blue) with them at all times in case their symptoms worsen.”
"We also advise people with asthma to continue to manage their condition with their preventer inhaler (usually brown) as this will help to reduce the inflammation in their airways and make them less likely to react to asthma triggers," Dr Whittamore said.
What are the two types of dust?
Calima is the Spanish word to describe when there’s sand or dust in suspension in the atmosphere - with there being two types of this phenomenon.
Type A calima refers to natural haze from sand, dust and other particles that come from the environment.
Type B calima refers to the haze that comes as a result of pollution or ash from a forest fire.
Some of Spain’s larger cities struggle with poor air quality as a result of pollution, but the most striking episodes of calima come as a result of huge sand clouds from the Sahara blowing over to the Spanish lands.
Calima episodes tend to last between three and five days.
Have there been dust storms before?
In 2021 vast clouds were swept by trade winds across the ocean from Mali and Mauritania to the Caribbean and Florida.
Back in summer 2020, an enormous dust storm was dubbed “Godzilla” after winds swept nearly 24 tons from the Sahara to North and South America.
It was so vast that astronauts could see it from the International Space Station, tweeting photos of the dust cloud at the time.
NASA used satellite data and computer modelling to study the plumes.
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