Plants Play Larger Role Than Thought in Cleaning up Air Pollution

From the National Science Foundation:

“Plants clean our air to a greater extent than we had realized,” says NCAR scientist Thomas Karl, the lead author.

The National Arbor Day foundation has been saying the same things for years. About.com has this as item #6 in their Top 10 Reasons Why Trees Are Valuable and Important. Of course these pronouncements didn’t require an NSF Grant to find out. I can’t say enough positive things about trees, and I encourage readers to plant them at every opportunity.

Chemicals known as oxygenated volatile organic compounds (oVOCs) affect environment, human health

Photo of a forest with mountains in the background.

Poplars, aspens, other trees provide extensive “ecosystem services.”

Credit and Larger Version

Vegetation plays an unexpectedly large role in cleansing the atmosphere, a new study finds.

The research, led by scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., uses observations, gene expression studies, and computer modeling to show that deciduous plants absorb about a third more of a common class of air-polluting chemicals than previously thought.

The new study, results of which are being published this week in Science Express, was conducted with co-authors from the University of Northern Colorado and the University of Arizona. It was supported in part by the National Science Foundation (NSF), NCAR’s sponsor.

“Plants clean our air to a greater extent than we had realized,” says NCAR scientist Thomas Karl, the lead author. “They actively consume certain types of air pollution.”

The research team focused on a class of chemicals known as oxygenated volatile organic compounds (oVOCs), which can have long-term impacts on the environment and human health.

“The team has made significant progress in understanding the complex interactions between plants and the atmosphere,” says Anne-Marie Schmoltner of NSF’s Division of Atmospheric and Geospace Sciences, which funded the research.

The compounds form in abundance in the atmosphere from hydrocarbons and other chemicals that are emitted from both natural sources–including plants–and sources related to human activities, including vehicles and construction materials.

The compounds help shape atmospheric chemistry and influence climate.

Eventually, some oVOCs evolve into tiny airborne particles, known as aerosols, that have important effects on both clouds and human health.

By measuring oVOC levels in a number of ecosystems in the United States and other countries, the researchers determined that deciduous plants appear to be taking up the compounds at an unexpectedly fast rate–as much as four times more rapidly than previously thought.

The uptake was especially rapid in dense forests and most evident near the tops of forest canopies, which accounted for as much as 97 percent of the oVOC uptake that was observed.

Karl and his colleagues then tackled a follow-up question: How do plants absorb such large quantities of these chemicals?

The scientists moved their research into their laboratories and focused on poplar trees. The species offered a significant advantage in that its genome has been sequenced.

The team found that when the study trees were under stress, either because of a physical wound or because of exposure to an irritant such as ozone pollution, they began sharply increasing their uptake of oVOCs.

At the same time, changes took place in expression levels of certain genes that indicated heightened metabolic activity in the poplars.

The uptake of oVOCs, the scientists concluded, appeared to be part of a larger metabolic cycle.

Plants can produce chemicals to protect themselves from irritants and repel invaders such as insects, much as a human body may increase its production of white blood cells in reaction to an infection.

But these chemicals, if produced in enough quantity, can become toxic to the plant itself.

In order to metabolize these chemicals, the plants start increasing the levels of enzymes that transform the chemicals into less toxic substances.

At the same time, as it turns out, the plant draws down more oVOCs, which can be metabolized by the enzymes.

“Our results show that plants can actually adjust their metabolism and increase their uptake of atmospheric chemicals as a response to various types of stress,” says Chhandak Basu of the University of Northern Colorado, a co-author.

“This complex metabolic process within plants has the side effect of cleansing our atmosphere.”

Once they understood the extent to which plants absorb oVOCs, the research team fed the information into a computer model that simulates chemicals in the atmosphere worldwide.

The results indicated that, on a global level, plants are taking in 36 percent more oVOCs than had previously been accounted for in studies of atmospheric chemistry.

Additionally, since plants are directly removing the oVOCs, fewer of the compounds are evolving into aerosols.

“This really transforms our understanding of some fundamental processes taking place in our atmosphere,” Karl says.

-NSF-

Media Contacts

Cheryl Dybas, NSF (703) 292-7734 cdybas@nsf.gov

David Hosansky, NCAR (303) 497-8611 hosansky@ucar.edu

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50 thoughts on “Plants Play Larger Role Than Thought in Cleaning up Air Pollution

  1. ROTFLMBFOA no kidding Dick Tracy.
    MY those guvment scientist are really smart. Behind the times but smart just the same 😉 .

  2. what? they under estimated the uptake of VOC’s??
    what is a person to do…
    what else have they under estimated the ability of our earth to maintain balance?
    CLIMATE change, AWG, Disruption….. is it real or memorex?

  3. Gee, I thought I was just growing several thousand trees for the money when I cut them down. Who knew I was saving the planet? Reckon I can get paid the same for not cutting them down? 😉 Nahh.

  4. I tried to tell people that on digg. I said that people who burn oil and natural gas aren’t burning the forest. The bright fellow, Archiesteel he called himself, said both cause “AGW”. In fact the issues with deforestation are legion. Trees cool by shade and vaporization (must more significant than any effect of co2). Forests hold the soil and clean the water. Furthermore reinstatement of marshes could help to reduce the nutrients in water that is thought to harm coral (not global warming). There are legitimate environmental issues, co2 is at the bottom of the list.

  5. Conifers are the main source of VOCs (terpenes). I think this is a side effect of producing pitch, a natural pesticide.

  6. NASA began studies on this phenomenon as far back as the 1980’s, studying VOCs as they related to indoor spaces such as space capsules. They knew, studies published in 1984, that houseplants could remove compounds such as formaldeyhyde and benzene from the air, and the percentages relative to size of room and plant. Dr. B. C. Wolverton was involved in NASA designs for a lunar habitat.
    By 1996: How to Grow Fresh Air, by Dr. B. C. Wolverton, sold in the houseplant section of bookstores.

  7. Industrialized agriculture has made the U.S. the worlds “bread basket”. The use of grain alcohol in gasoline has caused an increase in the price of grain (surprise), forcing some people in the third world to “slash and burn” the rain forest. Whatever inconvenience these would-be lords of carbon cause developed countries will be insignificant compared to the misery they will levy on the developing world.
    “Gee, I thought I was just growing several thousand trees for the money when I cut them down. Who knew I was saving the planet?” – Curiousgeorge
    I also mentioned that foresting operations were one of the best friends of the forest! The “environmentalists” will put them out of business.

  8. DitelHead says:
    October 22, 2010 at 7:10 pm
    Industrialized agriculture has made the U.S. the worlds “bread basket”. The use of grain alcohol in gasoline has caused an increase in the price of grain (surprise), forcing some people in the third world to “slash and burn” the rain forest. Whatever inconvenience these would-be lords of carbon cause developed countries will be insignificant compared to the misery they will levy on the developing world.
    “Gee, I thought I was just growing several thousand trees for the money when I cut them down. Who knew I was saving the planet?” – Curiousgeorge
    I also mentioned that foresting operations were one of the best friends of the forest! The “environmentalists” will put them out of business.

    Fortunately, there are very few “environmentalists” ( or EPA critters for that matter ) in my part of the country. One could say they are on the endangered list. 😉 We do, however, have an abundance of good ol’ Southern boys and girls. 🙂

  9. Of course these pronouncements didn’t require an NSF Grant to find out. I can’t say enough positive things about trees, and I encourage readers to plant them at every opportunity.
    Excellent! May I add something else to consider, planting fruit, nut and berry producing trees at every opportunity. Not only are they healthy for you, they produce the most healthy, anti-toxin nutrition that nature provides. Even if you don’t eat what’s produced, wildlife and birds will benefit greatly. I’ve gone totally into planting fruit and berry producing trees on my land (Critter Junction) in the Ozark National Forest, Upper Buffalo Wilderness Area.
    There’s nothing better for a cool yard than a tree canopy! I leave a few open places with rye, clover and Kentucky bluegrass for the deer, turkeys and rabbits. I have 2 years of split firewood left from the Jan, 09 ice storm, both unfortunately & fortunately.
    Reminds me of the Ole Swimming Hole
    An man in Louisiana had owned a large farm for several years. He had a large pond in the back.
    It was properly shaped for swimming, so he fixed it up nice with picnic tables, horseshoe pits, some apple and peach trees. Place for family and friends to get together.
    One evening the ol’ farmer decided to go down to the pond, as he hadn’t been there for a while, and look it over.
    He grabbed a five-gallon bucket to bring back some fruit.
    As he neared the pond, he heard voices shouting and laughing with glee.
    As he came closer, he saw it was a bunch of young women skinny-dipping in his pond.
    He made the women aware of his presence and they all swam to the deep end.
    One of the women shouted to him, ‘We’re not coming out until you leave!’
    The old man frowned, ‘I didn’t come down here to watch you ladies swim naked or make you get out of the pond.’
    Holding the bucket up he said, ‘I’m here to feed the
    alligator.’

  10. Thanks, Ed Murphy
    You just made me laugh harder than at the last few pictures of Pachuri that I’ve seen. (really, who told that guy that his look is acceptable for a public face of an organization? He apparently needs to hire a few consultants of his own)

  11. So, let’s see: trees themselves emit volatile organic compounds (NB: the “smoke” of the Great Smokey Mountains). The VOCs react with ambient ozone, to make oxygenated VOCs. The trees then re-absorb the oxygenated VOCs.
    It’s not like trees need local ozone to oxygenate VOCs for them. They have a very sophisticated oxygen-activating metabolism. So, something else is going on. I’d wonder whether the re-absorbed oVOCs are reduced back to the parent VOCs and then re-emitted. A nice C-13 experiment would test that possibility.
    If so, the chemistry would be: VOC —-> oVOC
    O3 —-> O2
    oVOC —-> VOC (recycled in the tree)
    The VOCs and oVOCs cancel, with the net result: O3 —-> O2
    High ambient ozone is very irritating to trees and plants (and humans). So, maybe what’s really going on is that the trees and plants are managing their local air quality by removing some of the ozone. The whole operation may have nothing to do with removing hydrocarbon “pollution” at all.
    Ozone is produced naturally in air by the action of ultraviolet light (and lightning). So, one might expect trees to be more active in emitting and re-absorbing VOCs on hot sunny clear-sky days.
    I don’t think trees are especially bothered by ambient VOCs; especially their own. So, calling VOCs “air pollution” as Tom Karl does, is a bit tendentious.
    One might also guess that the VOCs are emitted in general to irritate and drive off predaceous insects.

  12. If trees absorb more a third more GW gasses, this could mean we’ll be paying foreign countries a third more to sequester our carbon…

  13. This really transforms our understanding of some fundamental processes taking place in our atmosphere,” Karl says.
    I’ve always described Earth’s natural systems as a large and complex tapestry. Some important parts are seen, some are not. As for the design, one can begin to see that long before the final weft thread is inserted.
    Regarding the above quote, where is it stated that every study that incrementally adds to our understanding of natural systems has to be reported as transformational? The measurement and documentation provided via this work can be appreciated. Does it transform our understanding of fundamental processes? Hardly. No more than the last short thread fundamentally transforms a tapestry. For those under a certain age: No more than the addition of the last pixel fundamentally transforms a 10 MB digital image.

  14. CRS, Dr.P.H. at 10:31
    A related item:
    This fellow, Eugene P. Odum, and others* studied “southern river swamps.” Someplace I have one of his small reports. I recall the statement that the swamps are like a kidney cleaning up waste products.
    I don’t know if Odum and Wolverton knew or worked with one another but they worked on related issues and in the SE USA.

  15. Ed Murphy > too funny 🙂
    If you would like to maximise yield from your fruit/nut woodland area, research “forest gardening” aka “food forest”. I can highly recommend a book by Martin Crawford (agroforestry.co.uk) – Creating a forest garden – there is some warmist group think opinionated within, but the plethora of plant advice makes up for it 😉 . Plant wise, it’s aimed at cool temperate zones, but the design concepts translate well to other zones – sub/tropical zones are covered well by Geoff Lawton on youtube/DVD. It’s really about stacking/layers using edible perennials and self seeders under the edible canopy layer, guilds of plants grouped for mutual benefit (e.g. N. Fixing shrub as scaffold for climber) to maximise yield for minimum effort.

  16. I am partial to small quantities of a particular oVOC myself. The particular one is C2H5OH.
    Organic compound Check (carbon based)
    Oxygenated Check (contains oxygen)
    Volatile Check (boiling point 78.4C)
    Long live some oVOCs (-:P

  17. Hamlet, Act 1, Scene V
    “There are more things in heaven and earth, Horatio,
    Than are dreamt of in your philosophy.”
    Still true today!

  18. Plants Play Larger Role Than Thought in Cleaning up Air Pollution
    What is the mechanism by which Thought cleans up air pollution?

  19. The Victorians spent a lot of time and money planting trees all over British towns and cities to make the air better for people living in highly polluted industrial areas.

  20. Local lore is that the Blue Mountains behind Sydney Australia were named by Capt James Cook and crew incl. botanist Sir Joseph Banks, because the VOCs from eucalypts caused a blue haze.
    That was in 1770.
    Are the light absorption effects of VOCs included in climate models?

  21. Let me see if I have this correct. The more trees there are the less CO2 we have AND the less oVOCs. AND because, as we all know, people are cutting down trees at an ever alarming rate (and have been for hundreds of years), people are the cause of the rise in oVOCs AND CO2. Right?
    OK! So the solution to the world’s problems is simply to plant more trees. BUT, more trees means less room for people and, in the end, that equates to less people. Hummmmm…… is anyone else getting the feeling that we’ve heard this conclusion before? Maybe there’s really something to this AGW stuff. OR, maybe there’s too many people on this little planet and too few trees.
    Maybe….. naaaaaaaaaaaaaaaaaaaaah, it can’t be that simple. Can it?

  22. A much better study would be how many acres of very mixed forest could support a family in comfort. Fruits, nuts, timber, mushrooms, organic pork and chickens, charcoal, air cleaning credits etc.

  23. Ref – Grey Lensman says:
    October 23, 2010 at 5:58 am
    It might also be productive to see what the overall benefit would be to moving everyone out of the Western Hemisphere and back to the Eastern Hemisphere and letting nature take her course for a few million years. Siberia is rather underpopulated and I understand the Russian and Italian and French and Scandinavian and German and British and Spanish and Eastern European birthrates have fallen significantly and there’s plenty of room for everyone here to relocate there, and that the standard of living isn’t bad either. But, from what I’ve seen of the cost of homes over there on the Home and Garden Network, we’re probably going to have to sleep in tents for a few hundred years.

  24. Thanks Pete & Grey, I will have Anna look into your comments. She’s actually the one who persuaded this land use, though it was on my mind in the past. I should have mentioned the blackberry, dewberry and wild strawberries are all over the place. Persimmons, if you’ve never tried a persimmon beer, ya don’t know what you’re missing. Except for the cloud of gnats that follow you around for a week after you brew. Regardless of how much bathing you do.

  25. Thanks, Ed Murphy, I’m still chuckling a half-hour after reading your contribution.
    As to trees cleaning the air, I am sure we were taught this in school a half-century ago.
    My proudest memory from my first year in school was being selected to ‘help’ our Headmaster plant a tiny tree on Arbour Day. Last time I checked, it was still there and doing fine.
    How did we become so divorced, and so quickly, from understanding our natural environment?

  26. Larger Role Than Thought?
    Excuse me but it doesn’t appear that the NSF have been thinking.
    City planners have known about the importance of trees in streets and parks to maintain air quality for well over a century. Some could argue for almost 3 centuries. They figured it out without a grant. They used their senses and common sense.
    Next week’s announcement from the NSF will be what? That people with ten toes are more common than thought?

  27. “The team found that when the study trees were under stress, either because of a physical wound or because of exposure to an irritant such as ozone pollution, they began sharply increasing their uptake of oVOCs.”
    Poplars or “The Borg” as I like to call them, have many remarkable properties. If you break off a branch, the stress initiates a hormone response that causes them to start a new shoot. This suckering can lead to groves of genetically identical clones interconnected by the roots into massive single organisms. They can transport nutrients and moisture from rich micro-sites to poor ones and expand into otherwise hostile territory. When under stress they also seed like crazy. It sounds to me like this study merely observed this phenomenon. When the organism gets stressed, it “tries” to survive which manifests as new growth. This involves a higher metabolic rate and therefore higher oVOC uptake. This should surprise no one whose ever spent any time in the bush.

  28. Speed says: at 3:23 am
    Plants Play Larger Role Than Thought in Cleaning up Air Pollution
    What is the mechanism by which Thought cleans up air pollution?

    James Taranto of the WSJ in his “Best of the Web” writings frequently has one or more of these “thought” statements from newspapers around the world. It seems “thought” is capable of many sorts of things even if the mechanism is unknown. About like CO2 I suppose.

  29. From the headpost:
    ‘The results indicated that, on a global level, plants are taking in 36 percent more oVOCs than had previously been accounted for in studies of atmospheric chemistry.
    Additionally, since plants are directly removing the oVOCs, fewer of the compounds are evolving into aerosols.
    “This really transforms our understanding of some fundamental processes taking place in our atmosphere,” Karl says.’
    So – trees reduce oVOCs which in turn reduces aerosols.
    Non-carbon aerosols are classified as negative temperature forcings.
    Fewer oVOC-generated aerosols = positive temperature forcing.
    Interesting.

  30. James Bull says:
    October 23, 2010 at 4:24 am
    I think the only tree to grow really successfully in polluted London in Victorian times was the Plane. Many were planted in the 18th and 19th centuries none have yet died of old age.

  31. Several major problem with this – here are two:
    a) If it took studying DNA of the trees to determine how much oVocs were being metabolized, “36% more!” how’d they calculate the earlier “74%” if the trees metabolize the pollutants into non toxic substances (ie you can’t sample the sapwood or leaves to measure oVocs because they have been converted (to Carbon? sugar? CO2? and O2?). If they actually know and weren’t guessing how much before, why didn’t the article say so.
    b) What did they feed into the computer models that allowed them calculate the very accurate 36%? Surely the estimates of the global number of trees and the difference in response by species (poplar is particularly high) should have made the estimate 25-75%…or so more. Maybe even wider bars because do they know whether algae, grass, vegetables, shrubs, etc also do this?
    c) It seems that Thomas Karl and friends have “discovered” what a lot of people already knew about trees for a long time.
    “Plants clean our air to a greater extent than we had realized,” says NCAR scientist Thomas Karl, the lead author. “They actively consume certain types of air pollution.”
    Perhaps by “we” he means he and his few colleagues.

  32. I mean come on, is that not the very reason they selected and plante3d plane trees in London.
    An arboreal economy is very viable, producing income, crops and products throughout thee year along with land and forest management. You will be surprised, once you look into it, just how many things you can do, the forest berries are awesome.
    Distribution, reverse engineer the Supermarkets system. Think about that.

  33. Plants have to process large volumes of air to filter out a small amount of a trace atmospheric gas, carbon dioxide, to survive. During the process many larger molecules get trapped. One or more methods to automatically “clean the filter” are to be expected, as with this enzyme that breaks down oVOC’s.
    I wonder how well “cause and effect” has been considered in this study. More metabolic activity as with stressful conditions, more need for CO2, more filtering thus more of the enzyme produced, which means more oVOC’s getting broken down.
    Is “ozone pollution” really an irritant, or does it stimulate growth? Can they tell the difference?

  34. AND plants cause extra surface COOLING in response to extra CO2 through increased photo-traspiration COOLING as plants all grow faster when CO2 increases.
    See red-bold items (especially WeatherAction NewsNo27) via links in COMMENTS in the ongoing item on Climate Realists :-
    “World cooling has…..” =
    http://climaterealists.com/index.php?id=3307&linkbox=true&position=5
    This is an important aspect of feedbacks which ensure CO2 increases in the real atmosphere and biosphere (as opposed to half backed poltically-driven models) have ZERO climate effect. In fact CO2 is driven BY temperature not the other way around on long time scales.
    Thanks,
    Piers Corbyn

  35. Kadaka says
    Quote
    Is “ozone pollution” really an irritant, or does it stimulate growth? Can they tell the difference?
    Unquote
    Spot on

  36. Where’s the news?
    Years ago, when hitch hiking, I got talking to the driver, who ran his own tree ‘surgeon’ business. He explained how planting the right types of trees at the roadside would…
    a) remove the pollutants
    b) help the trees to grow as they thrived on those pollutants.
    He explained that sycamores, IIRC, were good for road sides, Scotch pines were good for other areas, oaks again for different parts. He went through many tree species & their ideal placement.
    There’s nothing new here.
    DaveE.

  37. Understand Karl’s points are pure spin to allow EPA to push forward its disastrous new ozone standard of 60ug/l. The problem is trees and soil NOx will cause natural violations in large areas of the country. Karl’s claims seem to describe the process by which trees produce Isoprenes to protect itself against ozone damage particularly to the photosynthetic components and diminish lipid peroxidation of cellular membrane. Some of this isopren is “readsorbed” in these processes. However vast quantities are still released into the atmosphere. There is no larger source of VOC to the atmosphere than plant derived isoprene. Free radicals (OH) convert the Isoprene into a secondary organic aerosol- an organic epoxide that when colliding with an acid particle in the atmosphere is “kicked” to form a glue agglomerating the particles, causing some precipitation and reduced visibility.
    Consider EPA has reduced ozone action levels to 75ug/l and are in the process of lowering them to 60ug/l. (despite the CDC finding no link to asthma) The only way many forests and near forests will be able to meet these new standards is to cut them down. Any number of long term existing ozone monitoring stations in Maine, Smoky Mountain area (isoprenes are what caused the smog and the name) South Dakota show these rural areas are dominated by plant isoprene precursors.
    If we look at ozone episode days (>90ppb) along the west slope of CAs Sierras over 70% is the contribution is froom isoprenes. Consider tree friendly urban cities such as Atlanta where the anthropogenic component of the background hydrocarbons is only 24%…. Isoprenes represent 53%!
    The other pieces of the ozone precursors comes from soil bacteria NOx and lightning. These natural sources overwhelm man’s contribution. So EPA is going to lower a standard for ozone to a level that cannot be met by natural background conditions. And its monitoring programs will be so designed to show that all ozone precursors come from refineries, chemical facilities and autos. People that frequently read this site will intuitively understand how the system will be designed to hide the natural inputs.
    The 60ug/l standard will have massive impacts on our refining, chemical industries and automotive sectors. It needs careful watching.

  38. “I can’t say enough positive things about trees, and I encourage readers to plant them at every opportunity”
    I would second that! I plant trees where ever I can, they not only clean the air, but provide habitat for wildlife, reduce flooding, reduce erosion, change the climate etc…. and you can get a lot of joy from watching them grow.

  39. Interesting topic, but bad writing. First, the information density was way too low. The whole article could have been condensed into one medium-sized paragraph.
    Second, we readers are big boys and big girls; we’re not afraid of them thar big words. However the authors did not mention a single specific example of a oVOC that trees cleanse from the troposphere. Commentators here have mentioned a couple of candidates: formaldehyde and oxidation products of terpenes.
    Unfortunately, these problems are not unusual in pop sci writing. Hey, science writers! Show some respect for your readers, and don’t waste our precious time.

  40. Richard says: October 23, 2010 at 1:29 am
    I am partial to small quantities of a particular oVOC myself. The particular one is C2H5OH.

    I’m sure some folks are not appreciative of your exhaled aldehyde aerosols.

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