A new study suggests classic paintings by renowned artists Joseph Mallord William Turner and Claude Monet may have been influenced by air pollution during the Industrial Revolution.

The study, published in the Proceedings of the National Academy of Sciences by authors from Harvard and Sorbonne universities, analyzed 60 oil paintings by Turner from 1796 to 1850 and 38 paintings by Monet from 1864 to 1901.

Researchers say as the “atmospheric reality” in London and Paris changed due to industrial pollution, so did the artists’ work to reflect a hazier landscape by using a whiter colour palette.

Scientists don’t know exactly how polluted the two cities were during that time because of a lack of data. However, researchers say examining the works of Turner and Monet paint a picture of long-term environmental change consistent with air pollution.

According to the authors of the study, stylistic changes in Turner’s and Monet’s works “are consistent with the optical changes expected from higher atmospheric aerosol concentrations.”

In particular, researchers said changes in local sulfur dioxide emissions from burning coal may explain changes in the colour contrast and intensity of Turner, Monet, and others’ works—even after taking into account the artistic trends and subject matter of the time.

In short, the study suggests Turner and Monet documented the incremental increase of pollution in London and Paris in their paintings.

HOW DO RESEARCHERS KNOW?

Scientists have successfully been able to measure painters’ accurate depiction of nature in the past, pointing to differences in local weather patterns influencing colour saturation in works painted in certain parts of Europe versus others. The authors of the study say paintings done in Britain generally feature a paler blue sky than other works in other parts of the continent.

Using the knowledge that artists can historically accurately depict their environment, the authors chose to focus on Turner and Monet because they are famous for their landscape and cityscape paintings and because they were active during the Industrial Revolution, when air pollution grew at an unprecedented rate.

Additionally, researchers say as the air in London and Paris became more polluted, the cities would appear hazier to the naked eye as well as in photographs. By comparing the paintings of Turner and Monet to pictures from the era, they were able to determine the artists were at least partly influenced by the change in emissions.

The study concludes Turner’s and Monet’s paintings provide “proxy evidence” for historical trends in pollution before a method for scientists to measure emissions in the air became available. The authors found a correlation between the environments at the time and the colour contrast in the artists’ paintings.