Fog, smog, pea soupers and the Saharan dust storm: What are they and how dangerous can they be?

Just how dangerous can air pollution mixed with Saharan dust be?

Areas of Britain are experiencing "very high" levels of air pollution caused by a mixture of local and European emissions and dust blown up from the Sahara desert.

Government health advice has been issued amid warnings that the pollution will spread across England and Wales and again hit high levels later this week.

But just how dangerous can air pollution mixed with Saharan dust be? And how does this phenomenon differ from ordinary smog or fog?

Here's our short guide to all things foggy.

FOG.

Fog is essentially a cloud on the ground.

It is formed by tiny water droplets suspended in the air. According to the Met Office the official definition of fog is a visibility of less than 1,000m.

This limit is appropriate for aviation purposes, but for the general public and motorists an upper limit of 200m is more realistic.

Fog tends to be thicker in industrial areas where there are pollution particles which moisture can form on.

It differs from mist only in intensity. Mist is formed in the same way but is not as dense.

There are a number of different types of fog including advection fog, which occurs when moist air passes over a cool surface and is cooled and upslope fog, which occurs when hill fog forms when winds blow air up a slope.

Aside from the obvious transport problems associated with freezing and other types fog, it is relatively harmless.

SMOG

The term "smog" was first used in London during the early 1900's to describe the combination of smoke and fog.

Typically the term is today used to describe a mixture of pollutants, typically vehicular emissions, with fog.

Smog was a serious and dangerous problem in London in the 19th century to the mid 20th century as fog mixed with the burning of large amounts of coal resulting in a thick, cloudy mixture of smoke and sulfur dioxide.

Today, the term refers to what happens when sunlight reacts with nitrogen oxides and volatile organic compounds, which are emitted from cars, forming ground-level ozone.

Ground-level ozone is responsible for the choking, coughing, and stinging eyes associated with smog.

PEA SOUPER FOG

Black fog or killer fog, also known as a pea souper, is a very thick dense, green-yellow fog caused by air pollution formed from soot particles that result from the burning of coal and the poisonous gas sulfur dioxide.

It was a particularly hazardous and regular sight on the streets of London up until the 1950s. The worst example of its deadly impact occurred during the Great Smog of London of 1952. 12,000 additional deaths were reported in the city over a couple of days.

The deadly smog led to the passage of the Clean Air Act 1956 which banned the use of coal for domestic fires in urban areas, and greatly reduced the occurrence of the black fog.

A pea souper, or 'London Particular', is formed in the same way as ordinary smog but is thicker. In the 1952 smog the air was so thick that visibility was reduced to a couple of yards or less.

 

SAHARAN DUST STORM

The current high levels of air pollution have been caused by Saharan dust along with a mist of toxic air which has mixed with other pollutants from Europe on route to the UK.

A map showing levels of pollution forecast for Wednesday A Defra spokeswoman said: "The high level of air pollution this week is due to a combination of local emissions, light winds, pollution from the continent and dust blown over from the Sahara."

The elevated pollution levels have been caused by dust blown up from the Saharan desert combined with pollutants in the continental air flow.

Defra has warned that those with existing lung and heart conditions may find their symptoms worsening, and said they should avoid doing too much, especially outdoors.

Even healthy people are advised they could experience minor symptoms including a sore throat or tickly cough and should avoid strenuous activity in order to reduce such symptoms.

News
A model of a Neanderthal man on display at the National Museum of Prehistory in Dordogne, France
science
News
Richard Dawkins dedicated his book 'The Greatest Show on Earth' to Josh Timonen
newsThat's Richard Dawkins on babies with Down Syndrome
Arts and Entertainment
Eye of the beholder? 'Concrete lasagne' Preston bus station
architectureWhich monstrosities should be nominated for the Dead Prize?
Extras
indybest
PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
News
ebooksAn evocation of the conflict through the eyes of those who lived through it
Travel
Dinosaurs Unleashed at the Eden Project
travel
Arts and Entertainment
music
Sport
football
Life and Style
This month marks the 20th anniversary of the first online sale
techDespite a host of other online auction sites and fierce competition from Amazon, eBay is still the most popular e-commerce site in the UK
News
i100
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Quantitative Analyst (Financial Services, Graduate, SQL, VBA)

£45000 per annum: Harrington Starr: Quantitative Analyst (Financial Services, ...

Application Support Engineer (C++, .NET, VB, Perl, Bash, SQL)

Negotiable: Harrington Starr: Application Support Engineer (C++, .NET, VB, Per...

C# .NET Software Developer (Client-Side, SQL, VB6, WinForms)

Negotiable: Harrington Starr: C# .NET Software Developer (Client-Side, SQL, VB...

C# Developer (Genetic Algorithms, .NET 4.5, TDD, SQL, AI)

£40000 - £60000 per annum + Benefits + Bonus: Harrington Starr: C# Developer (...

Day In a Page

Middle East crisis: We know all too much about the cruelty of Isis – but all too little about who they are

We know all too much about the cruelty of Isis – but all too little about who they are

Now Obama has seen the next US reporter to be threatened with beheading, will he blink, asks Robert Fisk
Neanderthals lived alongside humans for centuries, latest study shows

Final resting place of our Neanderthal neighbours revealed

Bones dated to 40,000 years ago show species may have died out in Belgium species co-existed
Scottish independence: The new Scots who hold fate of the UK in their hands

The new Scots who hold fate of the UK in their hands

Scotland’s immigrants are as passionate about the future of their adopted nation as anyone else
Britain's ugliest buildings: Which monstrosities should be nominated for the Dead Prize?

Blight club: Britain's ugliest buildings

Following the architect Cameron Sinclair's introduction of the Dead Prize, an award for ugly buildings, John Rentoul reflects on some of the biggest blots on the UK landscape
eBay's enduring appeal: Online auction site is still the UK's most popular e-commerce retailer

eBay's enduring appeal

The online auction site is still the UK's most popular e-commerce site
Culture Minister Ed Vaizey: ‘lack of ethnic minority and black faces on TV is weird’

'Lack of ethnic minority and black faces on TV is weird'

Culture Minister Ed Vaizey calls for immediate action to address the problem
Artist Olafur Eliasson's latest large-scale works are inspired by the paintings of JMW Turner

Magic circles: Artist Olafur Eliasson

Eliasson's works will go alongside a new exhibition of JMW Turner at Tate Britain. He tells Jay Merrick why the paintings of his hero are ripe for reinvention
Josephine Dickinson: 'A cochlear implant helped me to discover a new world of sound'

Josephine Dickinson: 'How I discovered a new world of sound'

After going deaf as a child, musician and poet Josephine Dickinson made do with a hearing aid for five decades. Then she had a cochlear implant - and everything changed
Greggs Google fail: Was the bakery's response to its logo mishap a stroke of marketing genius?

Greggs gives lesson in crisis management

After a mishap with their logo, high street staple Greggs went viral this week. But, as Simon Usborne discovers, their social media response was anything but half baked
Matthew McConaughey has been singing the praises of bumbags (shame he doesn't know how to wear one)

Matthew McConaughey sings the praises of bumbags

Shame he doesn't know how to wear one. Harriet Walker explains the dos and don'ts of fanny packs
7 best quadcopters and drones

Flying fun: 7 best quadcopters and drones

From state of the art devices with stabilised cameras to mini gadgets that can soar around the home, we take some flying objects for a spin
Joey Barton: ‘I’ve been guilty of getting a bit irate’

Joey Barton: ‘I’ve been guilty of getting a bit irate’

The midfielder returned to the Premier League after two years last weekend. The controversial character had much to discuss after his first game back
Andy Murray: I quit while I’m ahead too often

Andy Murray: I quit while I’m ahead too often

British No 1 knows his consistency as well as his fitness needs working on as he prepares for the US Open after a ‘very, very up and down’ year
Ferguson: In the heartlands of America, a descent into madness

A descent into madness in America's heartlands

David Usborne arrived in Ferguson, Missouri to be greeted by a scene more redolent of Gaza and Afghanistan
BBC’s filming of raid at Sir Cliff’s home ‘may be result of corruption’

BBC faces corruption allegation over its Sir Cliff police raid coverage

Reporter’s relationship with police under scrutiny as DG is summoned by MPs to explain extensive live broadcast of swoop on singer’s home