Subject: Re: Biology Question on Trees and Polution

From: [email-masked] (Jim Cook)
Date: 18 Mar 1995 04:57:18 GMT

In article <[email-masked]>, 
[email-masked] (Mark Thorson) says:
>
>In article <[email-masked]>,
>Gerod Wattier <[email-masked]> wrote:
>>Hi, I hope there is a biologist out there that can answer this question.  
>>I work with an educational institution that teaches conservation to fifth 
>>and sixth graders.  We tell them how important trees are because they 
>>clean our air.  I've often wondered and have had the questioned asked how 
>>much polution do trees clean out of the air.  In the Pacific Northwest we 
>>have quite a few fir and alder trees.  For example how many average size 
>>trees would it take to clean up the polution from one automobile?  Does 
>>anyone have any information on that?
>>
>>Thanks Jerry
>>Carnation, Washington
>>[email-masked]
>
>I've crossposted this to sci.environment, where it should have gone in
>the first place.  Someone there might have the information you seek,
>however I think you'll be a bit surprised.  At least when you're talking
>about the hydrocarbons that contribute to haze and smog, trees CAUSE
>pollution, they don't cure it.

Simonich and Hites (1994) estimated that most of the atmosphere to soil
flux of polycyclic aromatic hydrocarbons (PAHs) occurs via absorption 
to plants.  They suggested that this may also be the case for other low
vapor pressure and hydrophobic atmospheric pollutants -- such as 
polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls.

It's true that trees and other plants release hydrocarbons to the 
atmosphere, and that these hydrocarbons contribute to the formation 
of smog and haze.  However, the rate limiting reactant in this 
photochemical reaction is NOx, which is largely anthropogenic in most
urban areas.
...Simonich, S.L. and Hites, R.A. (1994) Importance of Vegetation
in Removing Polycyclic Aromatic Hydrocarbons from the Atmosphere.
Nature, 370, 49-51.

---

From: [email-masked]
Date: Mon, 20 Mar 95 08:48:42 PST

In article <[email-masked]>, <[email-masked]> writes:

> ....Simonich, S.L. and Hites, R.A. (1994) Importance of Vegetation

Thanks for the citation...always a help. 
I'm not in this field, but it seems to me what you are saying is that, as 
part of the process of transpiration, trees and other plants will carry 
hydrocarbons disolved in the ground water into the tree, and then it will 
blow off in to the air.
Is it therefore correct to say that trees are only responsible for moving 
the hydrocarbons from the soil to the air?  That is, they do not *create* 
any of these things?  If so, then the question really is, how did the 
hydrocarbons such as dioxins get into the ground?

I'm sure Mr. Reagan would blame the ground-hogs.  and that Mr Thorson 
would believe him.

-tony

---

From: [email-masked] (Jim Cook)
Date: 21 Mar 1995 06:57:28 GMT

In article <[email-masked]>, [email-masked] says:
>any of these things?  

I guess I wasn't clear enough.  Trees and other plants make and release
a variety of hydrocarbons -- terpenes -- that are responsible for many
plant odors.  Generally speaking, plant roots don't absorb hydrocarbons
in the soil very efficiently.

>If so, then the question really is, how did the hydrocarbons such as 
>dioxins get into the ground?

PAHs, PCBs and dioxins get into the soil from the atmosphere -- except
for point source contamination.  And, for the most part, they get into
the air from human sources.  There's also some "recycling" of old
contaminants from soil and water reserviors.

>I'm sure Mr. Reagan would blame the ground-hogs. and that Mr Thorson 

Actually, Reagan was correct that "trees pollute," at least in a way.
However, as I noted, the rate limiting factor is [NOx], which mostly
comes from human sources.

That brings up an interesting point.  EPA could have attempted to
control either hydrocarbons or NOx to reduce smog and haze, and they
decided to regulate hydrocarbon emissions -- because it was less
expensive.  However, they found that less anthropogenic hydrocarbons
didn't necessarily mean less snog/haze -- given the background from
trees and other plants.  It turned out they need to reduce NOx 
emissions as well.  So it goes.

---

From: [email-masked] (Mark Thorson)
Date: Tue, 21 Mar 1995 15:18:46 GMT

>hydrocarbons such as dioxins get into the ground?

Trees are loaded with hydrocarbons which they make themselves.  A number
of solvents, such as DMSO, are by-products of the forest products industry.
Unless you live in coal country or on top of a chemical waste dump, there
won't be much hydrocarbons in the soil.

>I'm sure Mr. Reagan would blame the ground-hogs.  and that Mr Thorson 

And if the Natural Resources Defense Council said Rush Limbaugh emits 10%
of the methane going into the atmosphere, I'm sure anthonyp would send
them $15 to do something about it.

---

From: [email-masked]
Date: Fri, 24 Mar 95 13:04:35 PST

> them $15 to do something about it.

Sorry, no.  That would be like taking the republican approach to balancing 
the budget by targetting catagories that make up small proportions of the 
budget while ignoring those that account for 80% of it.

I thought Paul W.'s analogy was reasonable...Since things die everyday, it 
must be OK to commit murder.

One also must keep in mind that most of the volitile hydrocarbons plants 
produce have biological roles in the ecosystem.  The same cannot be said 
for most of that produced from human industry.
I don't think I would lump the D-limonine produced by my lemon tree 
in there with dioxin.

tony

---

From: [email-masked] (Mark Thorson)
Date: Mon, 20 Mar 1995 20:57:30 GMT

>polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls.

Polycyclic aromatics and the other compounds you mention are supposedly evil
chemical wastes, but are produced in small quantity.  Unless you happen to
live in Seveso, Italy, the real meaning of the word pollution mostly translates
into smog.  Trees, lawns, etc. produce volatile organic compounds (VOC's)
which become smog.

>photochemical reaction is NOx, which is largely anthropogenic in most

Around here, bread-baking plants have been required, at great expense, to
install scrubbers to remove ethanol from the proofing rooms for bread
dough (ethanol is produced by the yeast which make bread rise).  These
hydrocarbons are taken very seriously by the air pollution people.

---

From: [email-masked]
Date: 21 Mar 1995 03:27:17 GMT

> into smog.  Trees, lawns, etc. produce volatile organic compounds (VOC's)

Of course trees, lawns, etc. produce volatile organic compounds.
They always have, and always will.  The entire biosphere has evolved
to tolerate, and in many cases benefit from, these kinds and levels
of emissions.

The problem is the extra man-made VOCs, above and beyond the
naturally-occurring ones, different in very many cases from the
natural VOCs, and generated in vastly higher concentrations than
the natural VOCs, are not something that the biosphere has evolved
to cope with.

The Reaganite argument, which boils down to "trees generate VOCs
so we don't have to worry about man's air pollution" is a false
one.  It's like observing that death and killing occur all over
the natural world, so therefore murder must be OK.
> hydrocarbons are taken very seriously by the air pollution people.

You didn't mention where "here" is, so I can't really pass
judgement on the possible contribution of bakeries to the
overall organic compound pollution problem in your area.  But
I'll wager that if the same amount of money were spent to take
cars that fail emissions tests off the road permanently by
buying them from their owners, it would go further to reduce
air pollution than scrubbers in bakeries.  Unless your community
has a lot of bakeriers and few cars.

--PSW