But exactly how was anybody's guess.
Jason Surratt, assistant professor of environmental sciences and engineering at the Gillings School of Global Public Health, now reveals one mechanism by which isoprene contributes to the production of these tiny, potentially health-damaging particles.
The study found that isoprene, once it is chemically altered via exposure to the sun, reacts with human-made nitrogen oxides to create particulate matter. Nitrogen oxides are pollutants created by cars, trucks, aircrafts, coal plants and other large scale sources.
"The work presents a dramatic new wrinkle in the arguments for reducing man-made pollutants worldwide," said Surratt, whose work was published this month in the Proceedings of the National Academy of Sciences. "Isoprene evolved to protect trees and plants, but because of the presence of nitrogen oxides, it is involved in producing this negative effect on health and the environment."
"We certainly can't cut down all the trees," Surratt adds, "but we can work on reducing these man-made emissions to cut down the production of fine particulate matter."
With the precise mechanism now revealed, researchers can plug it into air quality models for better predicting episodes of air pollution and potential effects on earth's climate. The advance would allow researchers and environmental agencies to evaluate and make regulatory decisions that impact public health and climate change.
"We observe nature's quirks, but we must always consider that our actions do have repercussions," said Surratt. "It's the interaction between these natural and man-made emissions that produces this air pollution, smog and fine particulate matter -- and now we know one reason for how it happens."