Trees may be pulling their weight.
New research by government-backed scientists at the National Center for Atmospheric Research finds that deciduous vegetation absorbs one-third more air pollution than previously believed — tens of millions of metric tons worldwide.
The NCAR scientists, measuring air chemistry from Amazonia to Arizona, focused on some of the most pernicious pollutants — the so-called volatile organic compounds that people emit from vehicles, lawnmowers and coal power plants. These are abundant pollutants that, when mixed with sunlight and nitrogen oxide, form the ozone in smog hanging over cities such as Denver.
"Plant more trees, as long as they are the right trees," said NCAR physicist Thomas Karl, whose Boulder-based team's peer-reviewed report was published this week in the academic journal Science Express. "This will help reduce the levels of air toxics."
The right trees include ash, apple, birch, hawthorn, hackberry, maple, pear and peach.
Wrong: poplar, eucalyptus and oak, NCAR scientists say. These species, NCAR scientists say, emit more volatile organic compounds than they absorb.
Scientists long have believed that plants absorb the greenhouse gas carbon dioxide. The new research showing they consume huge quantities of organic compounds raises new possibilities for Denver — where city officials in 2006 embarked on a mission to plant 1 million trees by 2025 — and other cities facing tighter federal air-quality standards.
Federal environmental regulators have deemed Denver out of compliance for ozone. This week, Regional Air Quality Council members were brainstorming strategies for reducing volatile organic compound pollution, including land-use controls and fuel pricing and use of roadways and parking.
"Of course, we would love it if there was something that could suck up all the air pollution," air-quality council spokeswoman Sarah Anderson said.
A 10-member team at NCAR's Boulder lab relied on computer modeling, field observations from towers above forests and genetic studies to investigate the absorption of pollution through stomata pores in tree leaves. They used mass spectrometers to isolate and measure methyl vinyl ketone, a dominant organic pollutant.
Plants probably are absorbing other pollutants too, said Alex Guenther, section chief of NCAR's biosphere-atmosphere interactions group. While pine trees absorb pollution, researcher's aren't sure how much because the study focused on deciduous vegetation, including shrubs.
U.S. Environmental Protection Agency officials are compelling cities to come up with and adhere to plans for reducing air pollution. Cities that fail to comply face possible loss of federal transportation funding.
The NCAR team this week observed keen interest among climate-change scientists in their findings, because plant absorption of pollutants "has been somewhat ignored," Guenther said.
"It will be interesting to see what impact this has in an area like Denver," he said. "But tree-planting alone is certainly not going to solve Denver's smog problem."
Bruce Finley: 303-954-1700 or firstname.lastname@example.org