[Stoves] [Fwd: RE: [CarbonSIG] black carbon ** FINISHED this time **]

[CEDESOL Foundation lists]

There is an interesting and educational discussion going on through the 
CarbonSig lists that many of us should find relevant here on the stove 
list. 

-------- Original Message --------
Subject: 	RE: [CarbonSIG] black carbon ** FINISHED this time **
Date: 	Tue, 31 Oct 2006 10:22:19 -0000
From: 	Liz Bates <liz.bates at virgin.net>
Reply-To: 	carbonsig at hedon.info
To: 	CarbonSIG <CarbonSIG at HEDON.info>



Tami
This is really helpful - I've read it through slowly, and will read it again
as my understanding grows.

Being pragmatic, what I think I'm also hearing is that reductions in black
carbon and reduction in IAP both require the same solution - fuel-switching
to cleaner fuels and/or more complete burning of biomass. Would it be true
to say that increasing the dwell time of the gases before they reach the pot
(as per the rocket stove) would prevent the rapid cooling in your scenario
(b)?

It also makes trying to change the CDM 'ruling' on renewable / non-renewable
biomass all the more urgent and important.
Many thanks
Liz

-----Original Message-----
From: Tami Bond [mailto:yark at uiuc.edu]
Sent: 31 October 2006 02:22
To: carbonsig at hedon.info
Cc: Nikhil Desai
Subject: [CarbonSIG] black carbon ** FINISHED this time **



Hi everyone,

Let me know if this gets too technical. If so, we can take it to a
subset of interested parties.

First, other scientists have talked about black carbon reduction for
climate purposes as well-- so it is an unconventional idea, but not
completely weird.

 > 1. What is the difference, if any, between soot, smoke, and black carbon?

(a) Terminology; (b) Composition. 'Smoke' generally means any
particulate emissions from combustion, which could contain black carbon,
organic carbon, or mineral matter (ash). 'Soot' could mean the black
particles, and is used that way in combustion literature. Some people
use 'soot' to mean the same thing as smoke. However, I think that enough
people think of 'soot' as black particles, that the term is used in
popular discourse. 'Black carbon' is the climate scientist's term, where
'black' is used to indicate absorption of light. All this is rather
confounded by the fact that there are no chemical standards to calibrate
any mass measurements.

 > 2. Not all black carbon emissions have the same reflective property,
correct? You indicate that Chandra's black carbon in the lab was less
 > dark than yours in field tests.

Their black carbon might have been as dark as ours, but we had more per
fuel burned. But yes, it can vary in darkness and reflectivity
('absorption' and 'scattering' in optical parlance).

 > So I imagine is true of diesel engines as well - a car v. a truck v.
a generator - and may even be true of
 > the pattern of fuel use - a car at 5 km/h v. 120 km/h, or a generator
running at 20% load v. one at 100% load.

Absolutely. If you hear me talk about 'process-dependent emissions',
this is what I mean.

 > 3. What are the most important factors in producing darker particles
from a given fuel/technology mix - combustion temperatures?

(a) Poor mixing of fuel and air. BC is formed in slightly fuel-rich
zones of the flame. Hence high emission from burning in non-premixed
combustion such as solid fuels or diesel engines.
(b) Rapid dilution or cooling so that reactions stop, and can no longer
oxidize particles.
(c) Specific components of the fuel are prone to making BC-- aromatic
components-- and these are often found in solid fuels such as wood and coal.

 > 4. If so, it would be near-impossible to create good estimate of
black carbon emissions.
Yes, except for one saving grace: for atmospheric purposes, one needs
only the average over a number of events and emitting units, and I would
argue that one needs only the average to estimate mitigation purposes as
well.

It is nearly impossible to predict emissions from a single event (i.e.
car at 5 km/h), but I have some faith that we can eventually produce a
statistical average over multiple events (all the driving the car did),
*as long as* the range and types of relevant events are known. I believe
this is the difference between the Honduras measurements and the lab
measurements. Some event types have just not been included in the
operating cycle.

 > What is the reasonable level of uncertainty in current black carbon
emissions from fuel use (including diesel, coal,
 > biomass) and open (natural and manmade) burning of biomass?
Net emission = emission factor x activity level.
Do you mean total uncertainty in both?
Reasonable level of uncertainty is factor-two. Probably worse for open
biomass burning, which has a lot of interannual variability.

 > 5. I imagine the 30-day or one year GWP or radiative forcing of black
 > carbon in a given region would correspondingly be quite uncertain,

Yes. In addition to emission rate uncertainties, there are also
uncertainties about how quickly it is removed from the atmosphere, which
affects GWP.

 > YET
 > your modeling results indicate they may be huge (e.g., one-year GWP of
 > 10,000?). Correct?

Correct-- mine and everyone else's modeling results. Our estimate of GWP
was based on synthesizing results of 8 different global chemistry &
radiative transfer models.
A one-year GWP is bizarre, and I don't recommend even thinking about it.
Nevertheless, it would be upwards of 20k.

 > 6. If so, is it too simplistic to say, "Look folks, just as your local
 > temperature measurements are slightly affected by temporary heat
 > island effects, they are similarly affected by black carbon and other
 > aerosols in the region.

I think that we *did* say that-- sort of-- in policy analysis paper of
last year. But one can't think as simply as 'doing something about
warming.' Regional climate is influenced by temperatures and weather
patterns outside the region. I could have a discussion here about how
people need to define what they want to mitigate-- changes in
temperature or drying or rainfall or monsoon?-- but it would get too
long, and doesn't have a good answer anyway. One cannot simply add and
subtract CO2 and aerosols, because the aerosols are spatially different.

 > Just that few people have thought about how profound that finding is!

Climate modeling started looking species and hasn't gotten off that
horse. The community needs to get to a whole-source perspective-- some
GHG *and* NOx *and* ozone *and* aerosols are all switched on and off by
a single mitigation action-- but hasn't got there yet.

 > And your findings on black carbon make even a stronger statement,
"Switch to liquid or gaseous fuels, or to more efficient or less
 > polluting stoves, is the best way of lowering carbon load, whether as
GHGs or black carbon." Of course, if the first half of this para is
 > too simplistic, then the rest has to be revised.

I wouldn't call it carbon load but if you think in radiative forcing
terms, it is true in some locations, depending on what the dominant
sources are. Burn well and you are probably burning a lot; thus CO2 is
your long-term problem. Burn badly and you probably have little to burn,
some set of PICs (=product of incomplete combustion) is your short-term
problem even for climate, and that's OK because you have other
short-term problems and it would be a good idea to attend to both.

 > Don't mean to distract you from your work; short answers would suffice.

Reasonable questions demand reasonable answers.

Tami





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