[Stoves] Ultrafine particles (Re: Xavier

[Crispin Pemberton-Pigott]

Dear Xavier

This is not a complicated history.

>See if and how misguided is the WHO, and how misguided we are, as stovers.

As with the World Bank, there is a need for something to solve in order to get funding to do it. So any narrative that maintains a certain level of visibility among all the other problems is a plus.

The main problem is the science that the WHO relies on to generate its claims, not the WHO itself. The science falls into two categories : the toxicity of the particles under discussion, and the exposure one implies, that of course being connected to an emission => exposure=> inhalation => absorption => disease consequence for an individual or a whole population.

As we know, and mentioned many times, the single box model of air dispersion within a kitchen is very controversial because it is admited not to represent reality well and the WHO’s own investigation into a three box model shows that emissions could be more than twice as high from the stove to get the exposures claimed for the single box model. In-kitchen measurements done by, among others, Omar Masera, show the single box exposure over-estimate to much more than triple.   The response by the WHO (members of that committee) was that the use of the single box model gave results that were ‘conservative’, which is to say, ‘Wrong’ by a factor of more than two (compared with their own three-box model).  It is common to use safety factors in health, but those are assessed and added at the end, not embedded into unjustifiable calculations.

The toxicity of particles is generally unknown so for the EPA to declare that all particles are equally toxic ‘because we do not known that they are not’ is plainly unscientific. I am not saying they can’t do it, they did, but there is nothing of substance in the claim.  It is not even ‘sciency’. It is arbitrary and contradicted by what is known about, for example particles of asbestos and tobacco which are well understood. They are not equal to each other in toxicity – how then could all other particles be equal to them?

>It seems we still have good reasons to want to lower the emissions of our stoves, even if we don’t know exactly how many lives we save (or we extend, depending on how you put it).

Common sense says we should reduce exposure to smoke based on obvious consequences (coughing, stinging eyes). That is a far cry from stating that we can calculate the increase in life expectancy for someone who avoids wood smoke at one level but is exposed to smoke of different origins at another level. The estimated consequence of changing the exposure is based on a Relative Risk (or Risk Ratio, RR) which is then used with a modeled exposure in a modeled kitchen. Having arrived at this « change » they then claim to be able to calculate the RR, which is a circular argument. C’mon !

We need to improve the understanding of the effects of quantified exposure, and we need much better estimates of what difference can be produced by fuel-stove combinations in various contexts, and some clear indication of how constrained those contexts are. That is why Samer and I wrote this paper<https://www.sciencedirect.com/science/article/pii/S2214629618301853>.

>Regarding the last EPA news: I am all for transparency. Given his reputation, I am not so certain about (nor confident in) what Scott Pruitt has set out to do, but we’ll see soon enough I guess.

Actions and results speak much louder than suspicious, projections and prejudice. In the same way that the EPA has built sets of regulations – quite expensive ones – upon poorly documented evidence, or secret evidence (which is not evidence at all), the WHO seeks to bring us «guidelines» that have poorly conceived or outright inappropriate logic underlying them. For example their present push to have fuels grouped into two sets : « clean » and « unclean » is founded on unreasonable assumptions about the performance of stoves. If you do not know how stoves perform, how on earth can you make claims about how well the fuel+stove combination works?

I have just reviewed tests of 9 biogas stoves from 8 countries. Is biogas a ‘clean fuel’ ? Only three of the stove would be permitted on the market in South Africa as cooking stoves based on the CO emissions alone.  All would fail safety and other performance requirements. All of them failed both the Indian and Chinese Standards. This shows that we cannot claim ‘biogas is a clean fuel’, nor can we say that ‘biogas stoves are clean’.

There is no substitute for performance testing, or toxicity testing for that matter.

Regards
Crispin

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