[Stoves] Between PM 2.5 and PM 10

[Julien Winter]

Dear Crispin and stovers;

RE: Just, B; Rogak, S; Kandlikar, M (2013) Characterization of
ultrafine particulate matter from traditional and improved biomass
cookstoves.
Environmental Science & Technology  47: 3506-3512   Doi: 10.1021/Es304351P


The article abstract I posted is certainly a teaser for those with a
keen interest in this area.  Crispin posed some questions about the
abstract that I will try to answer below:


The cookstoves they tested were (1) a 3-stone fire, and (2) the
“Chulika” rocket stove (distributed by iSquareD, Bangalore, India),
both burning sticks of hemlock; and (3) the fan-powered  “Oorja,” TLUD
stove (First Energy Ltd., Bangalore, India) burning commercial wood
pellets


> Something that is not clear from the abstract is whether the 'increase' in
> particles is an increase in the number of particles or an increase in the
> mass of particles, or an increase in the mass of small particles.

Number of particles.  Over a range of 15 to 660 nm particle diameter,
they measure the number of particles per unit volume of air, as a
proportion of the mass of carbon emitted during their period of
measurement to produce a graph of number of particles vs. particle
diameter.  The instrument was a TSI Scanning Mobility Particle Sizer
(SMPS) model 3080 with a custom differential mobility analyzer (DMA).



> " The 3-fold increase in quantities of sub-30 nm particles from improved
> cookstoves warrants further consideration by health scientists, with due
> consideration to the higher combustion efficiencies of improved cookstoves."

My interpretation is that there are trade-offs to be considered by
health scientists.  The efficiency of combustion increased from
3-stone < rocket < TLUD, (I suspect due to higher and more uniform
temperatures at the site of combustion in the TLUD compared to other
stoves), but there was a decrease in the size of particles emitted.
The increase in efficiency is good, because there is less fuel used
(fewer trees cut, less time gathering wood, less time cooking and
attending the stove), and a lower total mass of particles emitted.
Unfortunately, along with increased efficiency came a shift in the
spectrum of particle sizes emitted from larger soot particles that are
trapped in respiratory tract mucus, to nanoparticles that can make it
into the blood stream.  The dosage -- or concentration in the kitchen
atmosphere -- of particle sizes from various stoves has to be
considered along with changes in toxicological risk associated with
various particle sizes.  The health risk associated with nanoparticles
from combustion of biomass needs more research.  When all trade-offs
are considered, a better nutrition and quality of life may come from
using improved cookstoves, even though they may pose a new set of
health risks down the line.


> What does 'quantities' mean, exactly?

'Quantities' is vague language that seems to have escaped the
reviewers.  My interpretation is that 'quantities' is 'concentration
of particles', analogous to dosage.  '3-fold' is a rough abstraction
of their findings, because they are dealing with continuous gradations
of particle sizes.



> "Particles from improved stoves formed clearly defined chain agglomerates
> and independent spheres with little evidence of volatile matter ..."

This they observed using an electron microscope.  That paper gives
some pictures that show the particles from 3-stone fires to be much
larger and clumped than particles from the improved cookstoves.  The
particles from the improved cookstoves appeared more dense than
3-stone particles.  Since they measured a higher proportion of
elemental carbon in particles from improved cookstoves than 3-stone
fires, they reasoned that the particles emitted from 3-stone fires
contain more partially combusted volatile matter.


> This is extremely important to me - the lowering of volatile matter
> condensing into particles. The stove burning cleanly means getting rid of
> (by burning or not forming them) condensed volatiles. The health
> consequences from this fraction is far high than 'dry dust' though I
> understand that investigations of the ultra-fines are not nearly
> completed/understood.  Ultrafine particles (UF) are well distributed
> throughout the atmosphere so we have been living with the impact of them for
> a long time. Perhaps we will find BC UF is really bad for us, maybe not.

That is an interesting point that there is a natural background of
untrafine particles.  A question, though, is about how they were
formed, their chemical composition, and our level of exposure.  UF
particles from biomass fires are what we have evolved with, especially
if fire was domesticated by Homo erectus.

> Cigarette smoke is full of condensed volatiles so it is interesting to me to
> know if the comparison of PM emissions per se are 'equal to' cigarette smoke
> or akin to cigarette smoke, or not nearly as bad as cigarette smoke. It is
> quite possible that condensed volatiles from evaporated coal (which
> constitutes a lot of the emissions of an igniting coal fire in a poorly
> constructed stove - maybe 90%) are a bad as cigarette smoke. The main point
> is that the particles are not from combustion, not from almost the complete
> lack of it! Roasting fuel is a major source of PM. Cooling a flame against a
> cold surface produces PM of a very different nature.


> Thanks
> Crispin


For anyone interested in more details, I suggest that they get a copy
of the paper which can be purchased if need be.  The authors can be
found at The University of British Columbia, Canada, were I believe
Brian Just did this work for his M.Sc., supervised by Steve Rogak
(Mechanical Engineering Department) and Milind Kandlikar (Liu
Institute for Global Issues).

Regards,
Julien

-- 
Julien Winter
Cobourg, ON, CANADA