New Discovery - Your indoor air chemistry can be affected by your own oxidation field
A majority of our lives spend inside enclosed spaces such as residences, workplaces, cars and airplanes. Surrounded by potent chemicals produced by both outdoor sources and our own activities - like cooking or cleaning - people are constantly exposed to a variety of pollutants that infiltrate through openings in the interior environment. We ourselves provide compounds for indoor air contamination via exhalations from the mouth or skin; these chemical volatiles often find their way into spaces occupied with us!
Nonetheless, how do the volatile chemicals subside again? In the atmosphere outdoors, this is accomplished partially through natural processes such as rainfall or chemical oxidation. Hydroxyl radicals (OH) are primarily accountable for this purging of airborne pollutants. This alergenic molecule is aptly referred to as atmospheric detergents and it's mainly synthesized when UV light from the sun interacts with ozone and water vapors.
Indoor spaces, on the other hand, offer less exposure to direct sunlight and precipitation. Since highly filtered UV rays pass through glass windows without issue it has been generally assumed that OH radicals are present in lower concentrations indoors than outdoors and that ozone from outside intrusion is the primary contributor of oxidizing airborne chemical pollutants.
OH radicals are formed from ozone and skin oils
However, it has been ascertained that high levels of OH radicals can be generated indoors, simply due to the presence of people and ozone. This fact was revealed by a team led by Max Planck Institute for Chemistry in cooperation with researchers from the United States and Denmark.
The revelation that humans are not only capable of generating reactive molecules, but we have the power to transform them conversely was undeniably surprising to us," remarks Nora Zannoni, first author of the investigation presented in Science magazine and currently based at the Institute for Atmospheric Sciences and Climate in Bologna, Italy. According to Jonathan Williams' team, the strength and contour of the oxidation field is primarily a function of ozone concentration, its infiltration pattern into indoor spaces as well as ventilation configurations. Their research revealed OH levels comparable with those observed during daylight hours outside.
Oxidation fields are generated by the reaction of ozone with oils and fats on our skin, particularly unsaturated squalene which accounts for approximately 10% of all skin lipids that protect our visage. This transformation releases a plethora of gas phase chemicals containing double bonds that react further in the atmosphere with ozone leading to substantial amounts of OH radicals being generated as a result (+). The squalene degradation products were characterized and quantified individually via Proton Transfer reaction Mass Spectrometry and fast gas chromatograph-mass spectrometry systems. In addition, the OH levels could be empirically determined simultaneously to assess their level of reactivity.
The studies were carried out at DTU in Copenhagen, Denmark. Four test subjects resided inside a specially-tuned chamber under standardized conditions with/without ozone present; measuring their OH levels before/during their stay to determine its effect on health.
In order to comprehend how the human-induced OH field appeared during experiments, results from a tailored multiphase chemical kinetic model devised by the University of California, Irvine were combined with a computational fluid dynamics (CFD) model created by Pennsylvania State University - both based in America. Following the validation process, the modeling team scrutinized how OH radical concentrations varied under varying conditions of ventilation and ozone levels. From these findings it became apparent that OH radicals were being generated, abundantly present and forming distinct spatial gradients in each area.
"Our modeling team is the first and currently the only group that can integrate chemical processes between the skin and indoor air, from molecular scales to room scales,"
Manabu Shiraiwa, a professor at UC Irvine who led the modeling part of the new work.
"The model makes sense of the measurements -- why OH is generated from the reaction with the skin."
Shiraiwa, an associate professor at Tokyo University of Agriculture and Technology (TUAT), hailed the progress made in recent years by his team with regard to their investigation into indoor air quality under various humidity levels. "This study provides a new avenue for furthering research on this topic," he noted.
Methods for furniture and building materials
"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. OH can oxidize many more species than ozone, creating a multitude of products directly in our breathing zone with as yet unknown health impacts." This oxidation field will also impact the chemical signals we emit and receive," explained project leader Jonathan Williams, "and possibly help explain the recent finding that our sense of smell is generally more sensitive to molecules that react faster with OH."
In their latest study, scientists have revealed an intriguing finding that could impact our health: while some materials and furnishings are being rigorously tested before they can be sold, it is equally prudent to conduct tests in sync with people and ozone. Atmospheric chemist Williams opines this would provide a more comprehensive evaluation of the potential environmental effects. Oxidation processes can generate respiratory irritants such as 4-oxopentanal (4-OPA) and other OH radical oxygenated species, which may exert adverse effects on susceptible individuals. For instance, children and infirm persons are particularly at risk given their smaller size; inhalation of these substances may result in coughing or shortness of breath.
These findings are part of the study ICHEAR (Indoor Chemical Human Emissions and Reactivity Project) that brought together a consortium of collaborating international scientists from Denmark (DTU), the USA (Rutgers University), and Germany (MPI). Modelling was carried out as part of MOCCIE project based at UC Irvine, Penn State University-funded research initiatives.