NIST researchers studied the volatile organic compounds released by live Christmas trees and their interaction with ozone. They found that monoterpenes, the main volatile organic compounds, diminish over time and react with ozone to form low concentrations of formaldehyde. Research concludes that Christmas trees have little impact on indoor air quality for most people.

Live Christmas trees release chemicals called volatile organic compounds (VOCs). Some of these VOCs can react with ozone, a reactive gas, to create chemical irritants indoors. Chemical irritants are present in very low levels but may be a potential problem for those who are sensitive to them.

Every holiday season, Americans buy nearly 30 million live Christmas trees. Many families enjoy not only having a live tree in their home, but also the fresh scent it emits. The scent comes from chemicals called volatile organic compounds (VOCs). However, little is known about the emissions of volatile organic compounds and whether they have any health effects.

"Our nose is a great chemical sensor," says Dustin Poppendieck, an environmental engineer at the National Institute of Standards and Technology (NIST). "We know these trees are releasing something, so the question becomes: How big of a source is it? We want to explore which chemicals are being released, how much is being released, and relate that to other sources of chemicals in the house."

To answer these questions, Poppendieck and his NIST colleagues sealed a common Christmas tree, a Douglas fir, in a chamber. They then measured the amount and type of volatile organic compounds it released over 17 days. They also looked at whether volatile organic compounds might react with other components in indoor air to create new compounds.

The team's findings were published in the journal Indoor Environment.

NIST researchers placed a common Christmas tree in a sealed chamber for 17 days to monitor and measure the chemicals it released. These chemicals, known as volatile organic compounds (VOCs), give off the pine smell and can react with ozone to form byproducts. Researchers found low levels of these chemicals, which could be a potential concern for people who are sensitive to them. Source: M.King/NIST

The fresh smell often associated with Christmas trees comes from a group of volatile organic compounds called monoterpenes, which are also found in air fresheners, candles and some personal care products. Outdoors, coniferous plants, including most Christmas trees, release monoterpenes, which can affect outdoor air quality. However, little is known about how much monoterpenes are released when a Christmas tree is cut down and placed indoors.

Research has also shown that monoterpenes can react with ozone. Ozone in the upper atmosphere acts as a protective shield against the sun. At ground level, ozone is produced through a chemical reaction with light and can cause symptoms such as coughing and throat discomfort. Ozone also easily reacts with other chemicals in the air to form new compounds. Therefore, researchers are interested in observing the effects of ozone in the presence of trees indoors.

They placed the tree in an environmentally controlled chamber where the chemicals the tree gave off could be measured in real time. They measured volatile organic compounds emitted over a 17-day period using a technique that can detect organic compounds in the air, called proton transfer reaction mass spectrometry (PTR-MS).

In the experiment, the researchers simulated a home environment. They decorate the tree with typical holiday lighting fixtures and shine bright lights on the tree to simulate the day-night cycle. They turn off the lights every 12 hours and water the trees every day. They bring in outdoor air at the rate of a typical home and continuously measure the chemicals in the indoor air.

Monoterpenes are the most abundant VOCs emitted by this tree. They peak on the first day and decrease significantly by the third day. Poppendieck said their concentrations initially were the same as those found in plug-in air fresheners or in newly built homes, then quickly dropped by nearly 10 times. The researchers detected 52 different types of monoterpenes.

The researchers then injected ozone into the room and observed its effect on the chemical composition of the indoor air. They found that ozone reacts with monoterpenes to form byproducts such as formaldehyde, another volatile organic compound, and other reactive chemicals. With the introduction of ozone, monoterpene concentrations further decreased, while formaldehyde levels increased, indicating the impact of ozone on indoor air chemistry. However, the amount of formaldehyde produced is relatively small, about one part per billion. The average formaldehyde concentration in American homes is between 20 and 30 parts per billion.

For people who are sensitive to volatile organic compounds, Christmas trees can be a cause of watery eyes and noses, especially when they first move indoors. In this case, Poppendieck suggests opening a window near the Christmas tree can reduce exposure. Additionally, a freshly cut Christmas tree can be left outside or in a garage for three days before being brought indoors, as the intensity of the emissions naturally decays over time.

"But for most people," Poppendieck said, "it shouldn't be a big problem. I would still have a Christmas tree in my house."

Compiled source: ScitechDaily