The industrial fog that engulfed London in the Victorian era has long provided an enduring image of the capital.
Immortalised by the 19th Century novelist Robert Louis Stevenson, the notorious "pea souper" added atmosphere to his classic horror novelThe Strange Case of Dr Jekyll and Mr Hyde.
Sir Arthur Conan Doyle also used the lethal mixture of polluting chemicals to equal effect in his Sherlock Holmes books.
But in the absence of photographic evidence, literary descriptions have been the main source for a sense of what the famous phenomenon was like.
Paintings featuring the fog were discredited as unreliable due to the painters' tendency to use artistic licence.
However, the cloud of mystery is about to be lifted thanks to the art of a French painter and the work of two Midland academics.
Dr John Thornes and Dr Jacob Baker, from Birmingham University, have identified the date Claude Monet made his London paintings and what position the sun should have been in.
They have calculated the position of the sun depicted struggling to filter through the mist and smoke above the Houses of Parliament is accurate.
The discovery has been taken as evidence the artist did not make up the images from his French home.
"Art historians have been very sceptical about whether he painted what he saw or whether he painted what people wanted to see," said Dr Thornes.
"We have shown that the actual position of the sun in the sky was spot on compared to the letters he wrote to his wife, which means there is some real scientific data we can get from this source."
The academics calculate the London paintings were made from sketches Monet did in the capital between February 14 and March 24 1900 - just after the peak of the fog.
Further calculations made it possible to discover the exact spot where the French Impressionist artist sat - a second floor covered terrace of the former Governor's Hall at St Thomas' Hospital.
His paintings show three views of central London engulfed by mist. Further research is now planned to see if the colours used in the paintings are also correct.
"The bone of contention is whether these were the colours Monet really saw or did he exaggerate the colours," said Dr Thornes.
"That is the next stage of the research which will involve looking at the chemicals and trying to prove what sort of colours you would generate in the atmosphere with this level of pollution."
The 19th century London fog was caused by the massive use of coal to fuel the Industrial Revolution.
At its height, around the 1880s, visibility was reduced to just a few feet in the winter months.
Domestic use of coal also contributed to creating a perpetual haze above the city.
Contrary to the cosy images of domestic life peddled in Christmas cards, Londoners were in reality slowly poisoning themselves with their huge consumption of coal.
"You were lucky to live over the age of 50," said Dr Thornes. "Young people had rickets and bronchitis, pneumonia and asthma were the worst killers.
"People even walked into the Thames because they couldn't see where they were going. Visibility was never more than about a mile in London."
A succession of acts passed by Parliament helped improve things in the 20th Century. But ultimately it was to be the increased use of electricity and gas to power industry that cleared the air.