Human skin oils and ozone reacts to generate an oxidation field
A team of researchers led by the Max Planck Institute for Chemistry found that oil and fats on human skin reacts with ozone (a highly reactive gas composed of three oxygen atoms) to produce an oxidation field in indoor spaces. The reaction release a host of gas-phase chemicals containing double bonds that react further in the air with ozone to generate high levels of hydroxyl (OH) radicals. This oxidation field directly influences the chemistry of indoor environments around humans.
Our personal oxidative field
The discovery of an oxidative field around humans shows for the first time that human bodies also create OH radicals.
In the study, researchers asked three groups of four adults to sit in a climate-controlled stainless-steel chamber. Ozone was added to the chamber air inflow in a quantity that was not harmful to humans but representative of higher indoor levels. The team determined the OH values before and during the volunteers' stay, both with and without ozone.
The results showed that the OH radicals were present, abundant, and forming around human beings.
According to the study, oxidation fields are generated as ozone reacts to the oils and fats on our skin – particularly the unsaturated triterpene squalene compound that makes up about 10 percent of the lipids that protect the skin and keep it supple.
"The discovery that we humans are not only a source of reactive chemicals, but we are also able to transform these chemicals ourselves was very surprising to us," says Nora Zannoni, first author of the study and chemist from the Institute of Atmospheric Sciences and Climate in Italy.
The levels that scientists found were even comparable to outside daytime OH concentrations levels.
"The strength and shape of the oxidation field are determined by how much ozone is present, where it infiltrates, and how the ventilation of the indoor space is configured," says Zannoni.
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.
Hydroxyl Radicals (OH) in the atmosphere
The short-lived OH radicals are not harmful and are present in the outdoor environment. They are produced when sunlight breaks down ozone into oxygen atoms, which attack water to make hydroxyl radicals. These very reactive molecules are also called the detergents of the atmosphere as they neutralize other toxic molecules.
On the other hand, indoors are far less affected by direct sunlight and rain, which led to an assumption that the concentration of OH radicals is substantially lower indoors than outdoors. However, the new finding shows another mechanism for their formation. This raises questions regarding the potential long-term implication for our health.
"We need to rethink indoor chemistry in occupied spaces because the oxidation field we create will transform many of the chemicals in our immediate vicinity," says project leader Jonathan Williams.
Currently, various materials and furnishing are tested before being given the all-clear for sale. However, tests should also be conducted in the presence of people and ozone. This is because oxidation can generate respiratory irritants, which can have adverse effects, especially in children and infants.