Ozone exposure in indoor spaces makes the human body to generate hydroxyl radicals

Reviewed by Emily Henderson, B.Sc.Sep 1 2022

The human body's exposure to ozone in indoor spaces generates highly reactive hydroxyl (OH), radicals which are largely responsible for the oxidation of most pollutant gases, researchers report. The findings have implications for our understanding of the role of humans in indoor air chemistry and quality. "[The authors] observed that the human body interacts with the indoor environment in an analogous manner to how Earth interacts with the atmosphere," write Coralie Schoemaecker and Nicola Carslaw in a related Perspective.

"Both the human body and Earth are chemical reactors, consuming or producing oxidants and oxidized species in their surrounding atmospheres." The vast majority of humans spend most of their time indoors – whether at their home or workplace or while traveling between the two – and are exposed to a number of chemicals from various sources, including outdoor pollutants that find their way inside, gaseous emissions from building materials and furnishings, and products of activities such as cooking and cleaning. Moreover, the human body is also a potent mobile source of emissions.

Chemical removal of gas-phase pollutants in outside air during daytime is mostly driven by the production of OH radicals, which are formed primarily by the photolysis of ozone by ultraviolet sunlight. However, indoor air quality is much less impacted by this process, as glass windows largely filter out ultraviolet light. While research has shown that some OH radicals can be generated by other means in indoor environments, few studies have evaluated the chemical influence human bodies in these environments.

Through a series of experiments, Nora Zannoni and colleagues found that high concentrations of OH radicals are generated when people were exposed to different concentrations of ozone within a climate-controlled, stainless-steel chamber. According to Zannoni et al., squalene in skin oil reacted with to produce 6-methyl-5-hepten-2-one (6-MHO), which was key to establishing this human-induced oxidation field. What's more, they found that isoprene from human breath and products of its interaction with OH also react with ozone to produce more OH radicals, suggesting that humans are a net source of reactive oxidants indoors.