Junfeng “Jim” Zhang , Ph.D.,started his academic career studying how ozone pollution forms in the atmosphere. But one day he learned that some people can smell ozone – and he realized he couldn’t.
“This stimulated my interest in discovering why and how different people respond to pollution exposures differently,” said Zhang, professor of global and environmental health. After that, he changed his focus from the atmosphere to the human body.
Respiratory symptoms, such as coughing, chest pain, asthma attacks and COPD, are the most obvious effects of air pollution exposure. But while earning his doctorate in the 1990s, Zhang started to suspect that injuries to the lung were only the tip of the iceberg. “To prove this point,” he said, “I conducted research that contributed to the knowledge on how air pollution exposure affects the cardiovascular system.”
Over the next 30-plus years, Zhang and other researchers showed again and again the deleterious effects of air pollution on a wide array of organs and physiological processes. “It’s now very well known that air pollution affects almost every system of the human body,” Zhang said.
But with climate change ushering in new threats, including a growing risk of wildfires, Zhang and colleagues are shifting focus. While still quantifying harms, , they are increasingly asking a more urgent question: What can people do to protect themselves from the hazards in the air we breathe?
Proving the Point
In 2008, Zhang took advantage of a natural experiment – the 50% reduction in air pollution in Beijing during the 2008 Olympics – to measure the effect of air pollution on the cardiovascular system. He recruited young healthy medical students and trainees in Beijing and tracked blood pressure, heart rate, and cardiovascular biomarkers indicating the presence and degree of clotting, oxidative stress and inflammation. All the measures showed significant improvement during the Olympic games compared to beforehand.
A few years later, Zhang, who was helping with the establishment of Duke Kunshan University at the time, discovered the connection between particulate matter air pollution and cardiometabolic disorder and weight gain, which are both risk factors for type 2 diabetes. He raised one group of rats breathing the ambient, polluted air of Beijing, and another group of rats in an enclosure with an air filter. The rats breathing the polluted air, which had seven times the amount of particle pollution, had higher cholesterol numbers and blood sugar levels than rats in the filtered air. In addition, they and their offspring were more overweight.
More recently, Zhang and his students, working in Mongolia, have shown that influenza is transmitted more readily when air pollution levels are higher.
Taken together, these and other studies have demonstrated that breathing polluted air increases the risk for lung and heart diseases, diabetes, obesity, cancer, kidney disease, dementia and low-birth weight.
“I wish there was a safe threshold [of air pollution],” Zhang said, “but the more we dig into the data in the lab and in the real world through observation, [we see] there is no such thing.”
A family of herders near Ulaanbaatar,...
Mitigating the Harm
Air pollution comes in many varieties: ground-level ozone, sulfur dioxide, nitrogen dioxide, particulate matter and more. Outdoors, particulate matter comes from wildfires, prescribed burns, dust, pollen and fossil fuel combustion, among other sources. Indoors, particle pollution can be the result of smoking, cooking and cleaning.
Zhang is increasingly focused on particulate matter, particularly fine particles, which seem to be implicated in many of the documented pathologic processes. Once in the lungs, particles smaller than 2.5 microns (called PM2.5) can enter the blood stream, where they can interfere with circulation and travel to every part of the body.
Zhang has already shown that portable indoor air purifiers with HEPA filters can improve asthma symptoms in children. He is now working on a pair of similar studies among two groups of older adults in Los Angeles: one group with a history of heart disease and one group at high risk for developing type 2 diabetes. In the double-blind studies, participants use portable air purifiers with HEPA filters for several months and use the same units with the HEPA filters removed for the same amount of time. Zhang, his graduate students and collaborators are looking to see if the HEPA filters improve the health of the participants, as measured by lab tests including cholesterol and blood sugar levels.
As a result of his research, Zhang keeps several HEPA air purifiers in his home and office. He’ll turn one on in the kitchen when he’s cooking anything that produces smoke, steam or splatters. He also travels with a N-95 mask, which he uses in particularly polluted places.
Investigating Wildfires
In recent years, Zhang has turned his attention to wildfires that impact residential areas, called wildland-urban interface fires. Because they burn homes and vehicles in addition to vegetation, they emit particle pollution containing all manner of toxic chemicals. Unlike wildfires in remote forests far from human habitation, these fires directly affect large numbers of people, and the risks of such fires are increasing due to climate change and the continued construction of homes near forests and open spaces.
“Since the Clean Air Act,” Zhang said, “we have lots of efforts to control emissions from traffic and coal-fired power plants. In many places now, the number one air pollution source is wildfires.”
When the Eaton fire broke out in January 2025, Zhang quickly designed an add-on study to his ongoing research in Los Angeles to assess how well the portable air purifiers reduced fine particular matter indoors during the fire. Zhang showed that participants who were using the air purifiers with HEPA air filters had levels of PM2.5 indoors 15% lower than the participants who were using the units without HEPA filters, which he calls “significant but modest.”
Zhang is also leading a study on the Hawaiian island of Maui that will follow survivors of the 2023 Lahaina wildfire that killed more than 100 people. The study will track participants’ physical and mental health.
“The folks there are very concerned about long-term health effects,” he said. “They want answers and unless we do science to collect data, they won’t get answers."
