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U of T paper finds that indoor paints can absorb noxious gas, nitrous oxide

When illuminated, paints re-emitted some of the absorbed gas
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Indoor paints can absorb nitrous oxide gas and release it when illuminated by indoor lighting. CAROLINE BELLAMY/THE VARSITY
Indoor paints can absorb nitrous oxide gas and release it when illuminated by indoor lighting. CAROLINE BELLAMY/THE VARSITY

A recent U of T publication suggests that the paint on our walls might play a role in regulating our indoor environments.

Dr. Stephanie Jones is a postdoctoral researcher and the lead author of a study that claims that the noxious gas nitrous oxide (NO) in the environment can be reduced by the presence of indoor paints. The study found that NO is absorbed by the paint in the dark — but re-emitted with indoor lighting.

NO — an air pollutant known to harm human health — is an oxidant produced indoors by cooking, wood fires, candles, and cigarettes. It can lead to the production of ozone — a gas that, in certain situations, can negatively affect our health.

How can paint absorb gases?

The white paint used in this experiment contained a variety of chemicals, including titanium dioxide. Titanium dioxide and NO gas can react together to produce nitrogen dioxide and nitric acid. In the experiment results, levels of NO passing through the white paint cardboard sample decreased while levels of nitrogen dioxide increased.

In a written interview with The Varsity, Jones wrote that she and her lab believe that “the paint has a porous surface which allows some NO to be adsorbed. Recent findings… have shown that Volatile Organic Compounds (VOCs) diffuse through painted surfaces and provide support for our hypothesis.” According to lung.org, VOCs are gases that can react to form air pollutants.

When paints re-emit NO

The recorded decrease in NO levels in the air is correlated with an absence of light due to the absorbed NO diffusing into the paint. However, that same absorbed gas can also be released back into the environment.

Titanium dioxide is a photocatalyst, which sciencedirect.com defines as a material that absorbs light to induce a chemical reaction. “We believe that once NO is adsorbed into the paint it is converted into [nitrous acid (HNO2)] on the painted surface which is then photolysed by indoor lighting to release NO back into the air,” Jones wrote.

The process of photolyzation is when light energy decomposes a chemical compound. In this case, photolyzation occurs when HNO2 is decomposed back into NO with the addition of light, leading to the re-emission of NO gas.

A 2013 paper noted that indoor oxidative capacities were not properly understood, and the identification of indoor chemical reactions is inferior to those occurring outdoors. This is why any research done to explain how chemicals affect the air quality indoors can be beneficial to our understanding of the health effects of living indoors.

Jones cautioned that the results are only a start. “Further experiments are required to understand the implications for human health in indoor spaces,” she wrote.