As summer wildfire smoke choked Baltimore, UMBC air pollution researchers leapt into action

Starting this May, a series of wildfires in Eastern Canada sent enormous smoke clouds wafting into the U.S., triggering air quality warnings in cities from the Midwest to the Northeast. For days, orange skies backdropped landscapes clouded by acrid air. People who could hunkered inside with the doors and windows shut. Those who had to go out faced itchy eyes, burning throats, and worse.

As a resident of the Baltimore area—which was blanketed with particularly bad smoke in both early and late June—UMBC Professor Chris Hennigan looked at the haze with dismay. But as an environmental engineer who studies air pollution, he had an additional thought: “We were looking at the air quality forecasts, and we thought ‘We have to gather data,’” he says.

The public found many colorful words to describe the summer’s unwanted smoke: brutal, eerie, dystopian.

Hennigan and his team have been working to put numbers to the adjectives. On the roof of the engineering building, the researchers installed a squat, white sensor that monitors the levels of tiny particles in the air, particularly those measuring 2.5 micrometers in diameter or less—smaller than most bacteria. Called PM_2.5, these particles are released in large numbers during fires. They are dangerous to human health because they can work their way into the deepest parts of the lungs and even enter the bloodstream.

The sensor showed huge spikes in PM_2.5 when the smoke blew through, on some days reaching levels considered unhealthy for anyone to breathe.

The researchers also set up equipment to filter particles out of the air. After 24 hours, they collected the filters, which they are storing, neatly labeled, in a refrigerator in Hennigan’s lab.

The filtered samples will advance at least two ongoing investigations, Hennigan says. In one avenue of inquiry, Joel Tyson, Ph.D. ’23, biochemical engineering, is studying how tiny particles can harm human lung cells. Before this year’s smoky summer, Tyson had been studying the toxic effects of particulate matter normally found in the Baltimore air. With the new smoke samples, he will start to investigate whether wildfire smoke particles, per unit, are more toxic than regular urban particulate matter, which comes from sources such as cars and power plants. Some studies have indicated that wildfire particulate matter is indeed more toxic, but more research is needed before any definitive conclusions can be reached.

In another line of research, Hennigan is also studying how particles in the air, including from smoke, may affect the climate. Undergraduate chemical engineering students Danielle Larios ’25 and Luis Rodriguez ’25 are assisting in the investigations.

The researchers study how particles of brown-colored carbon-containing material absorb light. Burning vegetation sends large amounts of this brown carbon into the atmosphere. It’s possible that the particles are trapping significant heat from the sun, accelerating the pace of planetary warming. Such effects are not normally included in global climate models, and better understanding of the process could improve humanity’s ability to predict, and manage, the coming years of climate upheaval.

Climate change and wildfires are intimately linked. This summer was not only smoky, but also scorching. July marked the hottest month ever recorded, and scientists predict that as the world continues to warm, wildfires will continue to increase in quantity and intensity. “Smokeageddon,” as headlines put it, may become the new normal.

Hennigan says recent research illuminates how much wildfire smoke has contributed to air pollution trends. He points to a paper published in September in the scientific journal Nature that estimated that since 2016, wildfire smoke in the contiguous United States has undone around 25% of the progress in air quality made between 2000 and 2016.

For the researchers in Hennigan’s lab, those effects have been felt personally. 

Rodriguez recalled how in June he had to go out to buy a fresh pack of N95 masks. “The smoke was just awful,” he says. Larios says she felt a burning at the back of her throat in just 15 minutes walking to her car.

For Tyson, the effects of the smoke were so bad that at one point he struggled to breathe and had to visit the doctor. The episode, he says, drove home the importance of his toxicology research.

All three note both the complexity of the systems they are studying and the importance of discovering new knowledge that might help society handle the environmental challenges it faces.

“Our work can have real-world impact, and that’s exciting,” says Larios.