CO2 released after clearing

[coach210]

Hello,

I use the knowledge of each to have qq answers for a study that I must lead. I did a lot of research on the Internet without finding real answers.

For the construction of a road, 400 Ha of forest in Benin have been cleared. This clearing was done by bulldozing, and there was no forest fire. The trees were torn out and then left out. Their decomposition causes the rejection of CO2, but how much? Because a part of the carbon of a tree goes back into the earth and another part in the form of greenhouse gases including CO2. I would like to know the carbon percentage of a tree that is in the form of CO2 (I imagine there must be a number of parameters that come into play). moreover, once cleared, a layer of approximately 20 cm of material (laterite) is extracted to build the road, this layer is located under a first layer of about ten cm of topsoil. it seems to me that this must release the carbon in the soil, but how much? cleared land is not used later, or very little. I have also found many different figures on the amount of C per ha of forest depending on the zones, which is the most appropriate in this case. Thank you for your answers.

[jonule]

Hello,
the most important rejection in terms of decaying greenhouse gases is methane, CH4, which is 3000 times worse.
Why ? because its molecular composition is complex, it has more molecular bonds that return infra-red radiation (greenhouse effect, heat = infra-red radiation returned).
for CO2 and CH4 you can calculate the carbon mass C, but it will remain empirical values.
for these 2 gases these are "artificial" releases because created by man, it is the direct impact.

> Could you give the quantity in% of CO2 and CH4 for a tree decomposition?
finally, if the CH4 is burnt, it releases CO2, less worse for the greenhouse effect but still "artificial" ;-)

you can add: CO2 consumption of construction equipment, workers, their movement to the site etc, the manufacture of bitumen transport etc etc not counting equipment (panels, paint) and their manufacture and transport etc ... ahem it has to do a lot but it would be interesting to report to km!

[Christophe]

+ 1 with Jonule.

It's very complicated because it depends on the essence of the tree and the conditions of putrefaction ...

An easy approximation to remember is the following (European essence):

In CO2 without anaerobic digestion: 1 m3 of wood = 1 ton of CO2 absorbed .... therefore rejected (in the "worst" case)

On the other hand, it's been billions of years since forests died and are born ...

[coach210]

Thank you for your answers. I included in my study the CO2 released by the gear, the transport, the manufacture of the cement ... I focused only on the CO2 because it is the only gas that I can quantify relatively easily (I did not no data on gear pollution and relies on the fuel consumed to determine the quantity of CO2 released).

a m3 of wood absorbs 1 ton of CO2, stored in a different form. once the tree is dead, the carbon is released into the soil and in the form of gas, including CO2 and CH4. All the carbon is not released as CO2, so can we really say that a m3 of dead wood releases 1 tons of CO2?

[jonule]

no, it's really hypocritical.
the CH4 is good + worse than the CO2, and you ask if it passes by neglecting it?

the talk about greenhouse gases focused on vehicles as a carbon sink. no ch4 so spoke of co2.

BUT it is not only the vehicles as a carbon sink, there are all the other artificial activities created by the man, like the raising: was it necessary to eat as much meat and milk?
1 cow makes 15m3 of methane a day, one day it will pollute + that car.

a forest releases methane in the natural cycle. but a forest whose trees are slaughtered without valorizing them, we let them rot and release CH4: it is not nature that has chosen it, but man!

so :

a decomposing tree does not release CO2, so the reasoning you use is hypocritical, we have seen the source. this gives off carbon, but we can not say that 1 m3 dead wood releases 1 ton of CO2.

biodegradation, wikipedia:
"
However, in anaerobic environment, ie without oxygen, biodegradability is compromised: the materials generally do not deteriorate because of the lack of oxygen required for aerobic microorganisms. If biodegradation still occurs, it is an anaerobic process that produces methane, which is a greenhouse gas. However, this methane, if it is captured, is a source of energy. Its combustion will release carbon dioxide, also a greenhouse gas, but since this carbon originates from the atmosphere (fixed in a plant by photosynthesis), it is considered that this source of energy is neutral vis-à-vis of the greenhouse effect.
"

so according to wiki, all that is of plant origin is neutral in terms of greenhouse effect, so for your calculation we must not take into account the trees, it remains the vehicles.

which brings us to the "natural" greenhouse effect and the "artificial" greenhouse effect ... yet a tree can be planted by humans, right? even if it happens very rarely these days ...

remember that the H2O molecule is not diatomic and therefore has a greenhouse effect ... almost as much as CO2? let us remember that the cooling towers of the power stations reject clouds of H2O, and other molecules which have "mutated" therefore more complex from the molecular point of view, therefore + strong in terms of greenhouse gases: the infrared rays. red (heat) reverberate as many + as there are molecular bonds.
wiki source:
"
Greenhouse gases are gaseous components of the atmosphere that contribute to the greenhouse effect. The main greenhouse gases are water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (or nitrous oxide, formula N2O) and ozone (O3) . Industrial greenhouse gases include heavy halocarbons (chlorinated fluorocarbons including CFCs, HCFC-22 molecules such as freon and perfluoromethane) and sulfur hexafluoride (SF6).

Approximate GHG contributions from major gases:

* water vapor: 55%
* carbon dioxide: 39%
* ozone: 1%
* methane: 1%
* nitrous oxide: 4%

These gases have the common characteristic of absorbing a portion of the infra-red emitted by the surface of the Earth.
"
absorb = they send back to the earth etc ... = greenhouse effect

hey, the water vapor is more greenhouse than the CO2 do you realize Christophe? Do you think of the steam wells generated by the power stations? do they release CO2? not say eco-politico, do they release greenhouse gases? and yes! and they are real wells that work day and night.
but in short it is not (too much) the subject:

as much to look for "greenhouse effect":
http://fr.wikipedia.org/wiki/Effet_de_serre

[coach210]

I agree with you, the costing of CO2 is too targeted to be satisfactory. I initially limited to CO2 because it is the only gas that I could accurately quantify in a simple way (1L of consumed diesel product 2,64 kg CO2). it would surely be more interesting to carry out a carbon assessment, which would be less precise but will reflect reality.

at the level of clearing for me against it can not ignore it. from the moment when man destroys hectares of forest without compensation afterwards (no reforestation), we can not speak of a neutral balance sheet. there is a release of greenhouse gases caused by the man who is not compensated. otherwise, we can deforest the whole planet tomorrow and say, it does not matter, neutral balance ... I agree that it depends on the point of view and the scale adopted, but in the study that I perform I can not ignore the deforestation side.

I think I need to simplify my study to a carbon footprint, it is necessary to have a carbon equivalent adapted to each pollutant factor. I actually have to compare different pavement structures made with different materials and determine the least polluting structure. The main elements of pollution are:

x L of diesel (to be converted into carbon equivalent, but what coefficient is used, knowing that the equipment is very old and that I have no data on gear pollution)
y T of cement
z Ha cleared forest (the carbon equivalent coefficient is here too delicate)

thank you for your previous and upcoming comments

[jonule]

yes I would say to you "in the official definition, the carbon of wood is not taken into account in the figures of the greenhouse effect", this is what we read in wiki ... after saying that it does times ...


by looking a little on the net, I read that the wood (lignin + cellulose) green is composed of 30% about carbon, the dry wood of 50%.
but carbon alone is not a greenhouse molecule, unlike CO2 and CH4 ...

but how long does it take to decompose to the point of disappearing?
in the beginning the CH4 must intervene especially, then after a little CO2?