Researchers at the National Institute of Standards and Technology published a study Friday to determine the effect of compounds emitted by live Christmas trees on indoor air quality.
Americans buy nearly 30 million live Christmas trees every holiday season. Many families endure sweeping up pine needles to enjoy the fresh fragrance associated with having a live tree.
That smell comes from chemicals called monoterpenes, which are also found in air fresheners, candles and some personal care products. Until now, little was known about how much a single tree emits and whether it has any health effects.
"Our nose is a good chemical sensor," said Dustin Poppendieck, an environmental engineer at NIST. "We know that these trees are emitting something, and the question then becomes: How big of a source is it?"
Poppendieck and his team took a common type of Christmas tree, a Douglas fir, and sealed it inside a chamber meant to simulate a home environment. They decorated the tree in typical holiday lighting and shone bright lights on it to mimic the day-night cycle. They turned off the lights every 12 hours and watered the tree every day. They also brought in outside air at a rate typical for households, and constantly measured chemicals in the indoor air.
The presence of monoterpenes peaked during the first day before diminishing significantly by the third day. Their concentration was about the same level of a plug-in air freshener or a newly constructed house before dropping by nearly 10 times the original amount, Poppendieck said.
Monoterpenes also are known to react to ozone to form new compounds. Researchers injected ozone into the chamber to see how the monoterpenes would react. They found the reaction produced formaldehyde, which rose in concentration while monoterpene concentration diminished at an even faster rate.
The amount of formaldehyde created, however, was small at about one part per billion. Typical U.S. houses have formaldehyde concentrations ranging from 20 to 30 parts per billion, researchers said.
For people who are sensitive to airborne organic compounds like monoterpenes, Christmas trees could be the possible cause of watery eyes and noses. Poppendieck suggested opening a window near the tree to reduce exposure or to leave a freshly cut tree in the garage for three days before bringing it inside.
"But for most people," Poppendieck said, "this shouldn't be a major concern. I'm still going to have a Christmas tree in my house."
Poppendieck added people should water their Christmas trees every day, as the greatest risk to households is a dried-out tree, which can become a fire hazard.
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