[Stoves] Torrified Pellets

[Crispin Pemberton-Pigott]

Dear Ron

 

>It appears that the parameters for the WHO PM2.5 standard is 2mg/min of
_what_ _burning_ _level_ (i.e., we need a wattage parameter of some type)? 

Well, they have taken the EPA outdoor air quality approach as applied to the
EPA version of space heating stoves (which limits total emissions per home,
the way New Zealand does) and then projects that onto cooking stoves, as if
all stoves were of the same fire power. As you noted, the flaw is
fundamental.

Consider: We have typical homes in Java owning 4 stoves or more, as many as
7, with a wide range of firepowers. Which one is the allowed version? If the
WHO model of exposure (it is not based on measurements) assumes stoves can’t
be clean enough at some high power level, then inappropriate conclusions
will be drawn about all stoves. Even if the exposure and disease response
modelling were correct, someone with a small filthy stove would be allowed
and large stoves would not even if very clean burning per useful MegaJoule.
Thus we have a fundamental conflict between the WHO’s approach to health and
the ratings provided by nearly all stove tests.

There are two catches to this – one I just raised with Dean. The first is
the idea that there are ‘clean fuels’ that will not emit PM, or as much
anyway. The other is that there are ‘clean stoves’ that will not emit much
PM. Huh? If the emissions are related to the combination then any such
attribution is incorrect and ultimate meaningless (or grossly misleading).
We cannot attribute to a stove something ‘achieved’ by the fuel’. I won’t
repeat all that – anyone who missed it, please read my message to Dean.

>When an Italian university study concluded that an average unfiltered
cigarette at human-puffing speed (i.e., smoked in around 5 minutes) produced
more particulate than a modern, properly running 250KW diesel engine fully
loaded for an hour, it is important to link those 2 mg with an amount of
fuel combusted in that minute, don't you agree? 

Prof Lodoysamba in Ulaanbaatar was pointing out that even though their
ambient PM level is decried, often reaching 1500 µg/m3 in winter, annual
PM2.5 exposure is not as bad as living in a home with a single smoker.

I take your point about the exposure dose v.s. the total exposure. As
disease response is dose related, this is a major issue when determining the
effect of stoves. If a stove emits a little PM all the time, it may have no
effect at all. The same total emissions in an ignition period alone might
have a significant effect. Knowing only the total PM mass emitted cannot
give a very good prediction of health effects.

Here is a contribution to our discussion from a friend who works in this
(health) field:

++++++++++

If you ignore concentrations and exposures -- i.e., the real determinants of
disease - then fuel cycle emissions anywhere anytime become culprits in
disease. Remember, all the GBD [Global Burden of Disease] calculations begin
with fictitious fuel quantities, qualities, and aggregate locations; then
dubious emission factors are applied and the output put through even more
dubious atmospheric circulation models to cook up some concentration panels
in the model grids - maybe 20 km x 20 km, I don't know. Then put in some
rats - I mean people - in the grid, to calculate, for example, how many
pregnant women 12-15 are mulling about outside and how many are cooking with
fictitious wood in fictitious homes at what times; do the same for the rest
of the population as well, and with fictitious data about their health,
height, weight, age, maybe even length of the earlobe (just get a PhD kid to
establish some correlations and three papers are ready to roll). 

The rest is easy. Fictitious dose-response matrices and before you know it,
you've got an e-mail!! Your paper has been accepted for publication in
Science! In Nature! 

++++++++++

>P.S. Somehow I seem to be getting a feeling that the WHO standard is not
being chosen for proven health purposes, but rather for certain types of
fuels to be ultimately shown to be by definition "too dirty".  

The WHO is not exactly a Standard in the way we are talking about it – they
have a standard for annual, 24 and short term exposure; that is true. But
when calculating the effect of exposure based on the mass of PM emitted per
minute from a stove, that is not a standard, that is an exposure model. The
relevant document agrees that its single box model is not representative of
actual exposure because air does not move like that. Well, OK, they discuss
the limits of the model. They did not fix it and the exposure calculations
are at best dubious for that reason alone. Nigel Bruce (who might be reading
this list) and Nate Johnson said they are going to work on improving the
exposure models.

The main input value to the model is the PM emitted by the stove per minute,
but not for any ‘maximum’ minute, for the average. So, what if the exposure
and the response are not ‘average’? Kirk Smith has written enough on that to
convince me the dose/response is not linear. That means we need to know the
dose per time period that is meaningful such as the maximum five minute
average experience during the test (or similar). 

If we use gravimetric methods to determine average emission per minute, and
plug that into an admittedly unrepresentative exposure model, we have
doubled the problem: misreporting the critical values of exposure and
miscalculation the resulting exposure.  Calibrated light scattering PM
measurements can give real time calculated PM mass within 1% of the
gravimetric values, even pretty cheap ones. That is why we need
performance-based standards for the ISO, not some fixed method that we
already know will not be able to predict disease response. Reason? Most of
the money is coming into stoves because of disease claims. 

If the disease claims hold up to scrutiny, (not assured, apparently) so also
must the solutions proposed.

Regards

Crispin

 

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