Live Christmas trees affect indoor air chemistry: Researchers

Christmas trees emit chemicals which create the fresh scent commonly found in air fresheners, candles, and certain personal care products

Representative image of a Christmas tree (photo: DW)
Representative image of a Christmas tree (photo: DW)


Live Christmas trees release chemicals called volatile organic compounds (VOCs) that create fresh smell found in air fresheners, candles and some personal care products.

In the outdoors, conifers, the group of plants that includes most Christmas trees, release monoterpenes, and they can affect outdoor air quality.

But little is known about how much monoterpene is released when a tree is cut down and placed indoors during holidays.

“We know that these trees are emitting something, and the question then becomes: How big of a source is it? We wanted to explore which chemicals are emitted and how much, and to put that into the context of other sources of chemicals in a house,” said Dustin Poppendieck, an environmental engineer at the National Institute of Standards and Technology (NIST).

To answer these questions, Poppendieck and colleagues took a common type of Christmas tree — a Douglas fir— and sealed it inside a chamber.

They then measured the amount and type of VOCs it emitted over 17 days and also investigated whether the VOCs reacted with other components of indoor air to create new compounds.

They placed it inside an environmentally controlled chamber, where they could measure the chemicals emitted from the tree in real time.

They decorated the tree in a typical holiday lighting setup and shone bright lights on it to mimic the day-night cycle. The team turned off the lights every 12 hours and watered the tree every day.

The team brought in outside air at a rate typical for households, and constantly measured chemicals in the indoor air.

Monoterpenes were the most abundant VOC emitted from the tree.

They peaked during the first day before diminishing significantly by the third day. Their concentration was initially at the same level of a plug-in air freshener or newly constructed house before it quickly dropped by nearly 10 times its original amount, said Poppendieck.

The researchers detected 52 distinct types of monoterpenes, according to research published in the journal Indoor Environments.

For people who are sensitive to VOCs, Christmas trees could be one possible cause for watery eyes and noses, especially when initially brought indoors.

In that case, Poppendieck suggests, opening a window near the tree will reduce exposure. “But for most people, this shouldn’t be a major concern.”

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Published: 25 Dec 2023, 11:12 AM