Dangerously poor air quality conditions are affecting London and other parts of Europe due to a noxious mix of Saharan dust and urban air pollution sources. Residents of London have reported a red layer of dust that accumulated on all surfaces in the city following weekend rains.

The poor air quality in London as well as Brussels, Paris and Amsterdam, poses health risks to individuals with suppressed immune systems, respiratory ailments, and the young and elderly, in particular. Due to the combination of dust and urban pollution from cars, power plants and factories, the UK Department for Environment, Food and Rural Affairs (DEFRA) said the Air Quality Index has spiked to its highest, and most dangerous, level of ten across south England, the Midlands and East Anglia. The Air Quality Index is based on measurements of nitrous oxide, sulphur dioxide and ozone, among other pollutants.

At such a high level, DEFRA advises adults and children with lung problems, adults with heart problems, and older people, to "avoid strenuous physical activity."

Image: EUMETSAT

The air quality problems comes just two weeks after Paris experienced a multi-day air quality crisis, during which officials had to take measures to discourage driving, such as by making the city's vast public transportation system free to use.

A satellite operated by the European satellite agency EUMETSAT captured the Saharan dust being swallowed up by a storm that swept into northwest Africa, Spain, France and the UK during the last three days of March. The winds associated with this storm transported the dust 2,000 miles northward, according to the UK Met Office, which is the equivalent of the National Weather Service in the U.S.

“We usually see this happen several times a year when big dust storms in the Sahara coincide with southerly winds to bring that dust here. More dust rain is possible during showers expected later this week,” the Met Office's Paul Hutcheon wrote in a blog post.

Credit: U.K. Met Office.

Hutcheon says that winds of at least 20 miles per hour are required to lift Saharan sand to high altitudes, and in this case, winds were gusting above 40 miles per hour. "Saharan dust is also a contributing factor to air quality in addition to pollution levels and weather conditions," Hutcheon says.

Saharan dust can affect far more than just European air quality. By hitching a ride with high altitude winds, dust can be carried across the North Atlantic Ocean during the summer Atlantic hurricane season. When high amounts of dust are present, hurricane formation tends to be suppressed, because the dust interacts with cloud droplets in ways that prevent organized areas of thunderstorms from forming and transitioning into tropical storms and hurricanes.

An unusually high amount of Saharan dust was implicated as one of the causes of 2013's unexpectedly quiet Atlantic hurricane season, for example.

In Europe, the dust is expected to diminish during the next few days, easing some of the pollution problems.

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