The researchers will present their results at the fall meeting of the American Chemical Society (ACS) during the "Healthy Indoor Spaces: Bridging the Microbiome and Chemistry" symposium at McCormick Place. ACS Fall 2026 is being held Aug. 23–27.

"We showed that indoor ozone reactions with fragrances from cleaning produce nanoparticles that carry a respiratory dose comparable to or greater than what you would experience from standing outside along a busy road," says Boor, an assistant professor of civil and construction engineering at Purdue University who studies indoor air quality. "The particles are different in terms of their composition, but the total dose can be higher. You're not seeing smoke, dust or haze in the air. Instead, you think the air smells great, so it must be clean."

Boor and his colleague Nusrat Jung, a Purdue assistant professor of civil and construction engineering, started studying the impact of cleaning products and chemical disinfectants on indoor environments during the COVID-19 pandemic. In that work, they observed that many of these products are heavily scented. "That's often to create a pleasant smellscape in the indoor space," says Boor. "But clean air should not smell like highly concentrated citrus fruit. It should not really smell of anything."

Indoor chemistry speeds up

Atmospheric chemists previously established that terpenes emitted by plants, such as pinene from pine trees, react with ozone to create airborne nanoparticles. The nanoparticles aggregate and eventually grow large enough to seed clouds. But in forests, terpene levels are relatively low, so particle formation occurs slowly.