In Monet’s impressionist paintings, that dreamy haze is air pollution, study

Then, he writes in translated letters shared by the Tate art museum, gradually fires were lit, and smoke and a haze of industrial pollution returned to the skies. His work continued.

A new study, published Tuesday in the Proceedings of the National Academy of Sciences, analyzed changes in style and color in nearly 100 paintings by impressionist painters Monet and Joseph Mallord William (J.M.W.) Turner, who lived during Western Europe’s Industrial Revolution in the 18th and 19th century. The study found that over time, as industrial air pollution increased throughout Turner’s and Monet’s careers, skies in their paintings became hazier, too.

“Impressionistic painters are known to be exquisitely sensitive to changes in light and changes in the environment,” said atmospheric scientist Anna Lea Albright, lead author of the study. “It makes sense that they would be very sensitive to not only kind of natural changes in the environment, but also man-made changes.”

The early Industrial Revolution transformed lives and skies of London and Paris, the painters’ hometowns, in unprecedented ways. Coal-burning factories increased employment opportunities but obscured the atmosphere with harmful pollutants, such as sulfur dioxide.

Much of the change is apparent in the United Kingdom, which emitted nearly half of global sulfur dioxide emissions from 1800-1850; London accounted for around 10 percent of the U.K.’s emissions. Paris industrialized slower but still saw noticeable increases in sulfur dioxide in the atmosphere after 1850.

Air pollutants can heavily alter the appearance of landscapes, in ways visible to the naked eye. Aerosols can both absorb and scatter radiation from the sun. Scattering radiation decreases the contrast between distinct objects, making them blend in more. They also scatter visible light of all wavelengths, leading to whiter hues and more intense light during the daytime.

Turner, one of Britain’s most prolific painters, witnessed the dramatic developments in his lifetime firsthand — he was born in the age of sail in 1775 and died in the age of steam and coal in 1851.

In one of his most famous works, “Rain, Steam and Speed – The Great Western Railway,” he paints a train, at the time the latest engineering marvel that allowed people to travel at unprecedented speeds, about to run over a hare, Britain’s fastest land mammal. Details in the painting, however, could almost be difficult to discern — haze and mist obscure much of the painting, an underline of the growing air pollution.

The haziness in this painting was not a fluke or one-off incident either, according to the study. The team examined 60 paintings by Turner from 1796 to 1850 and 38 paintings by Monet from 1864 to 1901. Using a mathematical model, they looked at how sharp the outlines of objects were compared to the background; less contrast meant hazier conditions. They also looked at the intensity of the haze by measuring the level of whiteness; whiter hues generally indicated more intense haze.

Researchers found that around 61 percent of the contrast changes in the paintings largely tracked with increasing sulfur dioxide concentrations during that time period. (They also found a trend in whiter hues, but they put less emphasis on these results as pigments in the paintings themselves could have faded over time.)

The visual transformations are stark.

In Turner’s “Apullia in Search of Appullus,” which he painted in 1814, sharper edges and a clear sky are easily discernible. In “Rain, Steam and Speed – The Great Western Railway” painted 30 years later, hazy skies dominate. During that time, sulfur dioxide emissions more than doubled.

The beginning of Monet’s career also differs from its end. His “Sainte-Adresse” in 1867 heavily contrasts with his “Houses of Parliament” series that began around 1899, when he spent time on and off in London for several months.

The team also assessed visibility, the distance at which an object can be clearly seen, and found visibility in Turner’s clear-sky and cloudy paintings before 1830 averaged about 25 kilometers but decreased to 10 kilometers after 1830. In several of Monet’s…