Trees breathe in CO2 and exhale Oxygen A natural way to refresh the air or so it seems. Smog is a form of pollution. After years of scientific uncertainty and speculation, researchers at the University of North Carolina at Chapel Hill show exactly how trees help create one of society’s predominant environmental and health concerns: air pollution. It has long been known that trees produce and emit isoprene, an abundant molecule in the air known to protect leaves from oxygen damage and temperature fluctuations. However, in 2004, researchers, contrary to popular assumptions, revealed that isoprene was likely involved in the production of particulate matter, tiny particles that can get lodged in lungs, lead to lung cancer and asthma, and damage other tissues, not to mention the environment.