Smelly research could influence HVAC industry

Purdue University engineers have uncovered something disturbing about the type of artificial fragrances that are designed to make our homes smell fresh and pleasant.

While chemical products such as air fresheners, wax melts, floor cleaners and deodorants might conjure up the pleasant scents of nature, they rapidly fill the air with nanoscale particles that are small enough to get deep into our lungs and spread to other organs.

These nanoparticles form when fragrances interact with ozone, which enters buildings through ventilation systems, triggering chemical transformations that create new airborne pollutants.

“A forest is a pristine environment, but if you’re using cleaning and aromatherapy products full of chemically manufactured scents to recreate a forest in your home, you’re actually creating a tremendous amount of indoor air pollution that you shouldn’t be breathing in,” said Nusrat Jung, an assistant professor in Purdue’s Lyles School of Civil and Construction Engineering.

Jung and fellow civil engineering professor Brandon Boor are at the forefront of studying nanoscale airborne particle formation indoors and comparing it to outdoor atmospheric processes.

“To understand how airborne particles form indoors, you need to measure the smallest nanoparticles — down to a single nanometre,” Boor explained.

“At this scale, we can observe the earliest stages of new particle formation, where fragrances react with ozone to form tiny molecular clusters. These clusters then rapidly evolve, growing and transforming in the air around us.”

The researchers use a “tiny house lab” — a dedicated lab space for indoor air quality research that mimics a small home — in which they deploy the latest industry-developed air quality instruments to track how household products emit chemicals that evaporate easily, known as volatile chemicals, and generate the tiniest airborne nanoparticles.

Nusrat Jung and Brandon Boor in the tiny house lab. Image credit: Purdue University/Kelsey Lefever.

Called the Purdue zero Energy Design Guidance for Engineers (zEDGE) lab, the tiny house has all the features of a typical home but is equipped with sensors for closely monitoring the impact of everyday activities on a home’s air quality. Jung led the design of the lab, which was built in 2020 as the first of its kind.

While it’s yet to be determined how breathing in volatile chemicals from common household products impacts health, the two scientists have repeatedly found that when fragrances are released indoors, they react quickly with ozone to form nanoparticles. These newly formed nanoparticles are particularly concerning because they can reach very high concentrations, potentially posing risks to respiratory health.

Jung and Boor believe these findings highlight the need for further research into indoor nanoparticle formation triggered by heavily scented chemical products.

“Our research shows that fragranced products are not just passive sources of pleasant scents — they actively alter indoor air chemistry, leading to the formation of nanoparticles at concentrations that could have significant health implications,” Jung said.

“These processes should be considered in the design and operation of buildings and their HVAC systems to reduce our exposures.”

To continue learning more about chemical emissions and nanoparticle formation indoors, Jung and Boor are working with industry partners to test new air quality measurement instruments in Purdue’s tiny house lab before they are put on the market. Companies are drawn to the lab because it’s a more realistic setting than the chamber environments typically used for indoor air quality research and new product development.

As their research continues, Jung and Boor hope their findings will improve how indoor air quality is monitored, controlled and regulated.

“Indoor air quality is often overlooked in the design and management of the buildings we live and work in, yet it has a direct impact on our health every day,” Boor said. “With data from the tiny house lab, we aim to bridge that gap — transforming fundamental research into real-world solutions for healthier indoor environments for everyone.”

Jung and Boor’s air quality research is largely funded by the National Science Foundation, the U.S. Environmental Protection Agency and the Alfred P. Sloan Foundation Chemistry of Indoor Environments program. Their findings have been published in the journal ACS ES&T Air.

Top image caption: The tiny house lab at Purdue University. Image credit: Purdue University/Kelsey Lefever.