Statistics show that 90 percent of our lives are spent indoors, at the office, or in transportation. In such situations, many chemicals from different sources, eg pollutants or pathogens (bacteria and viruses).

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The air we breathe is naturally purified by hydroxyl (OH) radicals – highly reactive molecules, also known as “atmospheric detergents”, formed by the reaction of UV radiation, ozone and water vapor. But in confined spaces, the process is not so efficient. Sunlight is largely filtered through glass windows, the concentration of hydroxyl radicals is much lower indoors than outdoors, and it is hypothesized that ozone entering from outside is the main oxidant of chemical pollutants in the air.

It has now been found that high levels of OH radicals can be produced indoors – due to the presence of humans and ozone. The team showed it Led by the Max Planck Institute for Chemistry In collaboration with scientists from the USA and Denmark. Details are described in the journal science.

Nora Zanoni, lead author of the study, says:

It was surprising that we humans are not only a source of reactive chemicals, but can also transform them ourselves. The strength and form of the oxidation field is determined by how much ozone is present, where it penetrates, and how the internal space ventilation is arranged.

What is an oxidation field?

The oxidative field is created by ozone’s reaction with the oils and fats in our skin, especially squalene, which makes up 10% of the skin’s lipids, protecting it and ensuring its elasticity. This reaction releases several chemicals containing double bonds in the gas phase, which further react with ozone in the air to generate significant amounts of OH radicals. These squalene degradation products were individually quantified and quantified using proton transfer mass spectrometry and flash gas chromatography and mass spectrometry systems.

The experiment was conducted at the Technical University of Denmark (DTU) in Copenhagen. Four subjects were housed in a separate climate-controlled chamber under standardized conditions. To understand what a man-made oxidation field looks like, we combined the results of a detailed multiphase kinetic model from the University of California, Irvine, and a fluid dynamics computational model from Pennsylvania State University. In addition to testing in the laboratory, the scientists looked at how the man-made OH field changed under different ventilation and ozone conditions. The results revealed that there were strong spatial gradients in the presence and abundance of OH radicals.

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Prof. Manabu Shiraiwa of UC Irvine says:

Our modeling team is the first and currently the only group able to synthesize chemical processes between skin and indoor air from molecular scales to room scales. This model quantifies – why OH arises from reactions with the skin.

The new discovery also has implications for our health – currently, many products and household appliances are tested for chemical emissions in isolation before being put on sale. However, it is also advisable to test in the presence of humans and ozone.