Dust Removes Ozone From Indoor Air

Those dust bunnies hiding under the bed could help remove ozone from indoor air. Indoor dust contains flakes of human skin with significant quantities of chemicals that can react with ozone, according to new research (Environ. Sci. Technol., DOI: 10.1021/es103894r).

Charles J. Weschler of the University of Medicine & Dentistry of New Jersey, working with a team at the Technical University of Denmark, Lyngby, wanted to measure the chemicals squalene and cholesterol in dust, because the two compounds are major components of skin flakes that humans slough off. Squalene comes from the oil on the skin surface, whereas cholesterol is part of cell membranes.

Both molecules can help clean indoor air by reacting with the pollutant ozone. The gas can oxidize squalene and cholesterol, thanks to their carbon-carbon double bonds.

The researchers used gas chromatography-mass spectrometry to measure the chemical constituents of dust samples they had collected from 500 children's bedrooms and 151 daycare centers in Odense, Denmark.

In the dust, the team found significant amounts of squalene and cholesterol. Weschler was not surprised, since humans shed skin rapidly: People shed their outer skin layer every two to four weeks. Given the amounts of the compounds, Weschler estimates that dust could be responsible for 2 to 15% of indoor ozone removal, depending on the amount of squalene in the dust.

Weschler's team also found that the ratio of squalene to cholesterol was low: just 0.051 in homes and 0.052 in daycare centers. The researchers inferred from the low values that skin flakes, which have a higher ratio, were not the only source of these compounds. Extra cholesterol could come from cooking emissions, Weschler says.

Glenn C. Morrison, an indoor air expert at Missouri University of Science & Technology, Rolla, suggests an additional reason for the off-kilter ratio: Ozone might react to a greater extent with squalene than with cholesterol. While squalene has six double bonds, cholesterol has only one.

"Squalene is a tremendous scavenger for ozone," Morrison says. "If it is present in a building, it could significantly influence indoor ozone concentrations." He calls Weschler's estimate of ozone removal plausible.

However, the results may not be a reason to stop vacuuming. The reaction with ozone has a downside too, Weschler says. Some products of the squalene-ozone reaction could themselves be irritants. Plus, skin flakes could contain allergens or microbes, he says.

Morrison praises the work's emphasis on the impact of human bodies on their surroundings. "Just as we re-breathe our own exhaled air," he says, "our air quality is directly and indirectly impacted by the skin oils and skin flakes we deposit on surfaces."