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Re: Biology Question on Trees and Polution

In article <eeeD5Dx4u.DMv@netcom.com>, 
eee@netcom.com (Mark Thorson) says:
>
>In article <3ju7pe$s4m@usenetp1.news.prodigy.com>,
>Gerod Wattier <BCHP16A@prodigy.com> 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
>>bchp16a@prodigy.com
>
>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.
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