A Saharan dust cloud is set to take over London this week, the Department for Environment (Defra) has warned.
Londoners might face a “high” level of pollution that could affect their eyes and throat.
People with health problems have been advised to keep physical activity to a minimum.
Defra said in a statement: “There is a risk of Moderate or High levels of air pollution across parts of southern and eastern England on Thursday due to Saharan dust, although large uncertainties remain as dust has yet to be observed lifting into the atmosphere from the likely source region in west Africa.”
Each year over 9,500 people in London die due to air pollution, according to a study by the King’s College.
What is Saharan dust & how does it get to the UK?
Here’s an explanation from the Met Office:
Saharan dust is a mixture of sand and dust from the Sahara, the vast desert area that covers most of North Africa.
As in other parts of the world, the wind can blow strongly over deserts – whipping up dust and sand high into the sky. The wind in the upper part of the atmosphere then transports the dust in the direction in which it’s travelling, sometimes towards the UK.
Once it is lifted from the ground by strong winds, clouds of dust can reach very high altitudes and be transported worldwide, covering thousands of miles.
In order for the dust to get from up in the sky down to the ground, you need something to wash it out of the sky – rain.
When the raindrops fall, they collect particles of dust on the way down. Then when the raindrops land on something and eventually evaporate, they leave behind a layer of dust.
Paul Hutcheon, Met Office forecaster, says: “We usually see this happen several times a year when big dust storms in the Sahara coincide with southerly winds to bring dust here.”
In certain weather situations, Saharan dust can also affect air quality and pollution levels.