Did polluted skies influence Impressionist art?

In 1872 Claude Monet painted Impression, Sunrise (above)—a muted depiction of the port in the artist’s hometown of Le Havre, France. When the work was exhibited two years later, the journalist Louis Leroy offered a satirical review, writing that “wallpaper in its embryonic state is more finished than that seascape.” He also introduced a mocking nickname, inspired by the painting’s title, for Monet and like-minded artists: Impressionists.

The Impressionist art movement, which began in the 1860s, favored painting outdoors, representing everyday life, and capturing natural and transient light. That push for open air and sunlight came at a time when the air quality was dramatically worsening because of the Second Industrial Revolution. Generally dated from 1870 to the beginning of World War I in 1914, the period of rapid industrial development markedly increased pollutants in the atmosphere. (The UK had a head start on industrialization and air pollution—particularly in London, which earned the nickname the “Big Smoke"—because of the First Industrial Revolution from 1760 to 1830.) In addition to health and environmental concerns, such aerosols scatter light and thus change the appearance of objects.

Now climate scientists Anna Lea Albright of the Dynamic Meteorology Laboratory in France and Peter Huybers of Harvard University, with feedback from art historians, have investigated the potential relationship between atmospheric conditions and the transition from Romanticism and other earlier 19th century art styles to Impressionism. They analyzed 98 paintings by Joseph Mallord William Turner (1775–1851), whose later works presaged Impressionism, and by Monet (1840–1926), whose early work only hinted at the movement he’d later help found. The researchers tracked the shift from figurative to impressionistic style through the evolution from sharper to softer contours and toward a lighter color scheme and compared it with historical emissions estimates.

Aerosols absorb and scatter light indiscriminately. When artists look at an object, aerosols scatter away or absorb some light that would otherwise reach them, and the aerosols scatter into their eyeline some light that wouldn’t typically reach them. The net result is that the edges of objects become less distinct—that is, the contrast decreases—and overall the scene is brighter. You’ve likely experienced the effect on an especially foggy day, and Monet certainly did, as revealed in his The Houses of Parliament (Effect of Fog) from 1899–1904, shown to the right, which depicts a faintly discernible Palace of Westminster in London.

Albright and Huybers investigated the contrast of Turner’s and Monet’s paintings using wavelet analysis, which finds the color differences on length scales from individual pixels to the whole image. That information is then captured in a single value. The researchers used emissions of sulfur dioxide as a proxy for aerosol concentrations; burning coal, the powerhouse of the industrial revolutions, emits both particulate pollution and SO₂. A paper published five years ago estimated annual global historical emissions from 1750 to 2014 with city-level spatial resolution through a combination of 20th-century measurements, known emissions sources and their prevalence, and an extrapolation of trends back in time.

Visually, the older paintings have sharper contrast and darker colors than newer ones; for example, compare Turner’s Apullia in Search of Appullus from 1814 (on the left above) with his 1844 Rain, Steam, and Speed (on the right). The data for each artist show an exponential decrease in contrast over time and an increase in median intensity. But the data for both artists together do not form a continuous temporal trend: Monet’s works from the 1860s in and around Paris have comparable contrasts to Turner’s works from London 60 years earlier. Only Monet’s later paintings, started during his 1899 to 1901 trip to London, consistently dropped to the low contrasts seen in Turner’s later paintings around 1850.

Could changes in artistic styles over the century explain the disconnect between the temporal trends for each artist? Potentially, but the researchers found that much of the apparent mismatch is attributable to differences in annual emissions. By 1870, Paris had only just reached the level of London’s emissions in 1800. That delay in industrialization allowed the researchers to disentangle artistic trends from the influence of aerosols. Monet and Turner painted with similar contrast in environments with similar levels of pollution.

The contrast exponentially decreases, and the intensity increases, with respect to the local SO₂ emission at the time and location of the painting. The graph below shows the contrast results for the Turner and Monet paintings as well as a few by other Impressionist artists: James Whistler, Gustave Caillebotte, Camille Pissarro, and Berthe Morisot.

In their paper, the researchers argue that Impressionism “contains elements of polluted realism.” Their statistical model—which includes factors such as year, subject matter, and SO₂ emissions—accounts for 61% of the variance in contrast. The rest of the variation could be explained by artists’ personal preferences, changes in broader artistic tastes, and any number of things.

Historical evidence lends some additional support to the researchers’ conclusion. For example, in a letter to his wife around the time he produced the painting of Westminster above, Monet wrote, “When I got up I was terrified to see that there was no fog, not even a wisp of mist: I was prostrate, and could just see all my paintings done for, but gradually the fires were lit and the smoke and haze came back.”

To paraphrase Albright and Huybers, aerosols change the way we see things literally and, perhaps, even figuratively. Many cities in the recent past and currently have atmospheric pollution comparable to London in the 19th century. Art produced in those cities may show similar trends. (A. L. Albright, P. Huybers, Proc. Natl. Acad. Sci. USA 120, e2219118120, 2023 .)