The air we breathe is filled with a variety of contaminants. Outside, these can be eliminated by raindrops and the oxidation that results from the Sun's UV light interacting with ozone and water vapour.
What then occurs indoors?
The chemical cleaning that takes place via these hydroxyl (OH) radicals, brief-lived reactive species with the function of oxidising other molecules, happens through a combination of ozone leaking in from the outside and from the oxidation fields that we create around ourselves, as shown by a recent study.
Scientists have discovered that in some circumstances, indoor OH radical concentrations are comparable to midday outdoor concentrations. In other words, the quality of indoor air and human health are affected by the fact that we are walking, breathing, chemical reaction machines.
The Italian Institute of Atmospheric Sciences and Climate's atmospheric chemist Nora Zannoni explains, "We were really surprised to find that people are not only a source of reactive chemicals, but we are also able to alter these molecules ourselves.
In a unique climate-controlled chamber with ozone levels that approximated the top end of what you could ordinarily see indoors, the team conducted studies with three different groups of four individuals. Records of OH levels were kept before and after humans entered the room, with and without ozone present.
It was discovered that OH radicals were present, plentiful, and developing around the people by a mix of computational fluid dynamics modelling and actual air observations (partially involving mass spectrometry techniques).
The researchers discovered that ozone's reaction with the oils and fats on our skin, particularly the unsaturated triterpene squalene molecule, which accounts for roughly 10% of the lipids that protect and maintain the skin's suppleness, generates our individual oxidation fields.
"How much ozone is present, where it infiltrates, and how the ventilation of the indoor area is arranged impact the strength and shape of the oxidation field," claims Zannoni.
Our findings have significant implications for ensuring that the majority of the time we spend indoors is spent breathing air that is as clean and healthy for us as possible, something we are all acutely aware of as a result of the pandemic. It is estimated that we spend about 90% of our time indoors.
Although we have always known that oxidation processes occur indoors, it appears that under some circumstances, human-generated reactions predominate.
Understanding these processes is crucial since they could result in respiratory irritants as well as the removal of pollutants. Other indoor chemicals that may come from furniture, building materials, and scented goods should also be taken into account.
There is still a tonne of work to be done, too. For instance, the scientists are interested in learning how humidity levels affect the reactions and how the presence of additional individuals in a space may alter the situation.
Furthermore, it's possible that the oxidation fields that people create will even change how we perceive smell.
According to atmospheric chemist Jonathan Williams from the Max Planck Institute for Chemistry in Germany, "We need to rethink indoor chemistry in occupied areas since the oxidation field we create will change many of the molecules in our near surroundings."
Science has published the research.
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