Paintings by Claude Monet could shed light on pollution in London at the turn of the 20th Century, experts say.
The paintings may record of Victorian London's atmosphere
University of Birmingham researchers have pinpointed the dates and times of depicted scenes by analysing the position of the Sun in the sky.
The research also revealed the French painter's vantage point: a second floor terrace at St Thomas's Hospital.
The paintings give an accurate record of Victorian London's urban atmosphere, they write in a Royal Society journal.
Dr John Thornes, from the School of Geography, Earth and Environmental Sciences, said they had demonstrated that Monet's paintings contain accurate quantitative information.
"We are confident that these paintings show an accurate visual record of the urban atmosphere of Victorian London," he said.
Monet is known for his series of impressionist paintings showing the London skyline obscured by smog.
London's "great fogs" reached a peak in the late 1880s, then gradually declined, but very little is known about the nature and causes of air pollution at the time.
The great French painter made three trips to London in the autumn of 1899 and the early months of 1900 and 1901 to paint his London series.
They were finished at his studio in Giverny, France, after his final trip, but it is not known whether the canvasses brought back from London were almost or partially complete and whether they were based on real-life observations.
The scientists studied the position of the Sun in Monet's series of paintings of the Houses of Parliament begun on his second visit in 1900.
The towers and spires of the Parliament skyline provided markers for working out the position of the Sun in the paintings, giving accurate dates and times.
These were then compared to historical records of the dates Monet was in London.
"Monet's letters state that he observed the Sun on at least four separate occasions and these coincide with the main dates we have attributed to the paintings," said Dr Jacob Baker.
"We know that it would have been quite difficult to see the Sun due to cloud and pollution so Monet had to be very patient for the sun to appear.
"Using the information we have gleaned in this study, we can now go on to assess the information that Monet's paintings may provide on the atmospheric state and pollution of Victorian London."
They hope further detective work on Monet's famous paintings might yield clues to the scattering of light in the atmosphere and the particles that made up the fogs.
The research by the University of Birmingham pair is published in the Proceedings of the Royal Society A.
The Thames Below Westminster 1871 can be seen in the National Gallery's "Manet to Picasso" free exhibition, on display 22 Sept 2006 - 20 May 2007.