Jeff Masters Hurricane Blog

Don’t sleep on soot » Yale Climate Connections


Somesh Roy was about 10 years old when he discovered a history book depicting ancient cave paintings. The images captivated him. Inside his home in West Bengal, India, which lacked electricity, he used candlelight to gawk at the pages after dark.

“I knew I was going to be a historian when I grew up,” Roy says, flashing a smile to acknowledge his unconventional path. “Of course, if you’re going to be a historian, you become an engineer.”

Working both in the lab and classroom at Marquette University in Milwaukee, the mechanical engineer has carved out a unique specialty studying the molecular processes and behaviors of soot, a byproduct of combustion.

But Roy’s passion is painting a much bigger picture. “I’m researching how soot has influenced the formation of humans across the planet,” he says. And he’s sharing his findings in creative ways with the public.

His core message: Soot is a major — and often underestimated — substance influencing past, present, and future human evolution and well-being. As an example, soot, in the form of charcoal, rendered the earliest known human cave paintings. Soot also casts the yellow hue of a candle flame and tints the tones of sunsets. More broadly, and consequentially, the particle is generated and launched into the atmosphere nearly every time a gas-powered engine fires up.

Heavy exposure to soot is closely linked to cancer, respiratory diseases, and cardiovascular dysfunction. The World Health Organization has estimated that around 7 million people die annually due to exposure to polluted air, with particulate matter and black carbon — another term for soot — playing a significant role.

“Soot, literally and figuratively, lives in the shadow of fire and in many places without us realizing it,” Roy says. So he is making it harder for people to overlook.

Turning pollution into art

photo of a Brown man smiling and looking at a piece of art that resembles a child's mobile with large soot molecules dangling from it
Mechanical engineer Somesh Roy calls himself “a historian of soot.” He recently posed for a portrait with Tomás Saraceno’s 3D-printed depictions of soot particles. (Photo credit: Tree Meinch)

This spring, an assortment of jagged, chaotic black objects were suspended in the air within one nook of Marquette’s Haggerty Museum of Art. Each structure, between a golf ball and a tennis ball in size, was a 3D-printed, enlarged model of an actual soot particle observed in Roy’s lab. Hanging at eye level, they invited viewers to consider the sobering fact that we inhale these particles every day.

“I could imagine the damage a microscopic particle that shape could do in a person’s bloodstream,” says Katie Praedel, a Wisconsin Department of Natural Resources air monitoring specialist who has partnered with Roy on projects.

The dangling particles comprised one of several soot-inspired, interactive art pieces as part of an entire exhibit that Roy arranged this spring. The exhibition, featuring international artist and activist Tomás Saraceno, centered a theme: “We do not all breathe the same air.

To support Roy’s vision, the National Science Foundation last year issued him $550,00 in a coveted CAREER grant. This included allocated funds for the art exhibition and a series of urban air walks, in addition to his lab work modeling soot dynamics and particles.

For the public walks, Roy partnered with conservation groups and the Department of Natural Resources. Together they equipped Milwaukee residents with air sensors before strolling through urban spaces and parks, concluding with a talk about their findings. This helped illuminate for participants what they are breathing daily and how the immediate environment shapes air quality. Notably, a state air monitor near downtown Milwaukee recently measured the highest levels of PM2.5 of anywhere in the state. This sooty pollutant, when inhaled, can travel deep into the respiratory system and even enter the bloodstream — contributing to premature death from heart or lung disease.

“If you don’t see smoke, you don’t think of soot,” Roy says, underscoring a problem that perpetuates local inequities and global challenges. Because soot is generated from sources like manufacturing facilities and vehicle traffic, it often degrades the immediate air quality in local neighborhoods or regions and disproportionately harms Black and Brown communities.

Trees and shrubs can clean the air

In the classroom, Roy’s students regularly propose solutions or protective measures that people can take to offset the threat of soot. This includes planting trees and shrubs in your yard as clean-air barriers. The best options, according to a recent research project in one of Roy’s classes: plants with fine hairs or leaves with dense grooves and waxy surfaces that help trap air pollution before it reaches your lungs.

On the global scale, Roy recognizes that policy changes and regulations will play a vital role in air quality changes. New technologies are also key for capturing and limiting emissions, which is a natural application for his lab work investigating the origin of soot particles. Meanwhile, major climate events worldwide are turning public attention toward soot.

But can we clean up our act?

photo of the Statue of Liberty shrouded in smoke
A smoky haze from wildfires in Canada envelops the Statue of Liberty in Upper Bay on June 7, 2023, in New York City. (Photo credit: David Dee Delgado/Getty Images)

This past summer, for example, soot got personal for millions of people in the northern U.S. when record-setting Canadian wildfires sent waves of smoke southward. Hundreds of miles from the source, the smoke (aka soot) engulfed New York City in a pinkish-orange hue that resembled Cloud City from “Star Wars.” In other major cities, skylines turned subtly hazy or cloudy, while air quality readings plummeted to dangerous levels for humans and animals.

One unique aspect of these soot incidents is how they carry acute, immediate risk to humans as well as a broader threat to our climate. “Things that affect our health also affect climate and vice versa. They’re not two separate discussions,” says interdisciplinary researcher Tami Bond at Colorado State University.

Several years ago, Bond and colleagues conducted a benchmark, multiyear study that demonstrated that black carbon carries twice the climate-warming impact as previously thought. That work underscored that black carbon, along with methane, is the greatest human-generated contributor to global warming after carbon dioxide.

Although forest fires have released soot for millions of years, the Industrial Age escalated things with widespread fossil fuel use. Notably, this molecule was the root of the famous Great Smog of London event in December 1952.

That winter, a combination of excessive soot emissions aligned with unusual weather patterns to wrap London in polluted darkness for nearly a full week. The unprecedented five-day emergency ultimately contributed to an estimated 4,000 deaths. But then it prompted a historic public response. “That actually kicked off the first Clean Air Act in the modern era,” Roy says.

Today, he hopes that art, rather than a series of tragic events, might inspire the urgent responses needed for our health and the climate. “Art is a very good medium,” he says, “a mediator between everything in our lives.”





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