[Reproduced from the guardian, London]
London smog warning as Saharan sand sweeps southern England
The Met Office has forecast one of the year's worst smogs in London this week, following a combination of strong winds and powerful dust storms in the Sahara that has deposited fine red dust on the streets of southern England.
Cars in London, including the prime minister's outside 10 Downing Street, were covered in a thin layer of dust after overnight showers deposited the sand on much of the city.
Air pollution was expected to reach the highest level of 10 in London on Tuesday and Wednesday, the Met said. People with lung problems were advised to avoid strenuous exercise, and healthy adults were told to reduce exertion outdoors.
"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," saidPaul Hutcheon at the Met Office. "More dust rain is possible during showers expected later this week."
The Department for Environment, Food and Rural Affairs (Defra) said high to very high air pollution was expected across East Anglia, parts of south-east England and around the Humber on Tuesday. It attributed the high levels to light winds allowing the buildup of pollution, coupled with dust from the Sahara. High levels of air pollution in parts of the UK are expected to last until the weekend.
Defra air quality forecast for 2 April 2014. Green is low air pollution, orange moderate, red high, and purple very high. Photograph: DefraClean air campaigners said the government had a duty to warn people about the risks of pollution but was doing a minimal job. "In Paris, people were offered free transport, but the government here has been very quiet as they don't want to draw attention to this," said Maria Arnold, who runs the healthy air campaign for ClientEarth.
The Met said Saharan dust was lifted by strong winds and could reach very high altitudes. From there it can be carried by winds thousands of miles around the world. The dust gets caught in rain droplets in clouds, and falls to the ground when it rains. After the water evaporates, a thin layer of dust remains. It can also create vivid sunsets.
Generally, winds of more than 20mph are needed to lift sand from the Saharan desert, which has been experiencing gale-force winds of over 40 mph. The Sahara, the world's greatest expanse of desert, stretches about 3.5m sq miles across northern Africa. Its dust has been carried as far as Florida in the US, 5,000 miles away.
Saharan dust is a contributing factor to air quality, as well as pollution levels and weather conditions.
According to the World Health Organisation, air pollution has become the world's single biggest environmental health risk, linked to around seven million deaths a year – or nearly one in eight deaths in 2012. The figures released last month were more than double previous estimates and suggest that outdoor pollution from traffic fumes and coal-burning, and indoor pollution from wood and coal stoves, kills more people than smoking, road deaths and diabetes combined.
The UK faces fines of up to £300m a year and embarrassing court appearances after the European commission launched legal proceedings against it for failing to reduce "excessive" levels of nitrogen dioxide (NO2) air pollution from traffic, despite 15 years of warnings and several extensions and postponements granted to the government.
The worst case of smog to hit London took place in December 1952 when 4,000 people died prematurely and 100,000 fell ill.
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