[Stoves] News - coal and biomass pollution from Bhutan households

Sun Jan 8 15:14:23 CST 2017

Dear Nikhil

Well you have two really important quotes there:

And I am not referring to this one, which rather proves my assertion that people are claiming solid fuels cannot be burned cleanly enough to make a medical difference. Kirk’s number was ‘at least a 90% reduction’ (without saying from what to what, which undermines the concept of tiers) ‘which is only obtainable with fan stoves’. For Ulaanbaatar he said a 95% reduction would not be enough. [His ‘90%’ statement is widely cited in articles and by people making fan stoves.]

>However, pollution levels were still found to be higher than the WHO guidelines, which means improved cookstoves do not lower the pollutant concentrations to a safe level."

And not this on either (though it is good)

>“What business does ISO or GACC have to declare "a safe level" for the whole world?”

Rather:
>Is it the idea that the "safe" level be set arbitrarily so low as to drive out the biomass and coal industries out of business?
That’s one. ‘Yes’, is the answer. The war on coal was primarily run by Big Gas in the US, with ENRON leading the charge. ENRON was trying to get a monopoly on the gas supplies in the US when they went bankrupt.

>"Although there are health benefits from use of improved cookstoves, a desired health benefit can only be realised by switching to clean fuels such as LPG and electricity.”
That is the other. This encapsulates the goal (a desired health benefit, assumed to be calculable in some manner) and the mechanism: get rid of all solid fuels – and kerosene, don’t forget. It is specifically mentioned in many documents, thousands of them, as being a ‘dirty, smoky fuel’.

In most GACC letters there is a boilerplate final paragraph that says they are bringing clean fuels and clean cooking solutions to people who have traditionally been forced to use solid fuels for cooking – which is to say, solid fuels are inherently ‘dirty’ and have to be eliminated because using solid fuels exposes the cooks to high levels of PM2.5 and CO. Improved solid fuel stoves are only an interim measure due to circumstances that will, no doubt, be improved by massive subsidies as per Indonesia and India.

But there is more:

>“Alternatively, other strategies such as improving kitchen ventilation and changing cooking behaviour can contribute to lower health risks.”
Wait a minute. Improving ventilation is not included in the list of approved interventions, is it? We should look into that because it is blindingly obvious that putting the smoke outside is a huge benefit for IAQ.

And what is this about changing ‘cooking behaviour’? I think they meant ‘changing social behaviour’.

>“Educating parents to minimise the time spent by children inside kitchens during cooking will lower exposure since pollutant concentrations are high closer to the source and rapidly decay with distance from the source.”

That quote, right there, confirms the conclusion reached in the WHO committee creating the tiers and exposure simulations that their single box model does a really poor job of representing reality, and that their tested but unused three box model, which permits more than double the emissions rate from a stove in order to be ‘safe’, is superior.

If the multi-box model of air dispersion in the home provides adequate justification to resolve that children should keep away from the stove side of the kitchen because they get less exposure there, then it should also be used to cook up the exposure numbers. From those three-box model exposure numbers and modeled air turnover rates, one can in theory work the model backwards to an emissions rate from the stove. We were told when creating the IWA that the PM numbers for tiers were generated on the basis that dispersion modeling of kitchens (all from India as I recall) showed a particular exposure and that the exposure below a certain level was ‘safe’ and other not.

I take it from Harold’s detailed presentation on the assumptions made when considering exposure, that the ‘safe’ level was not attributable to wood stove smoke or coal stove smoke in particular, but to airborne particles in general, and the numbers were generated for whole populations, however defined.

I take it from Nikhil’s contributions that exposure to a particular type of smoke creates a health impact that has to be examined medically, and is affected by all sorts of things like inoculations and diet and age. That being the case, then what we learned from tobacco, silicosis and mesothelioma applies: exposure to particular types of PM (and size) is where the risk is and where safe levels can be assessed. Well, that doesn’t seem to have happened for wood smoke. When done for cigarettes, it took ages. Cooks are not exposed to all PM, they are exposed to biomass PM or coal PM or ethanol gel PM. Therefore ‘safe’ means something specific to do with biomass and coal, fuel by fuel. If you are saying ‘it is not safe at that level, it has to be this level’ this is the argument one must use to calculate an individual benefit.

This realisation creates an additional problem for setting the tiers. First, the model on which it is based is contradicted for ‘skill’ by the (rather obvious) advise to keep the kids away from the stove if they are in the same room. Second, the GBD numbers which underlie the claims for ‘safe’ and ‘not safe’ are derived for whole populations. But actual risk and relative risk derive from actual exposure to pollutants, not all pollutants.  The claim of the stove programmes is that they provide individual health benefits, even if difficult to quantify. Individual benefits are related to specific types of exposure, not ‘general population’ exposure. The health impacts of human skin particles, cement dust from the floor, Harmattan windblown dust, and PM from a diesel bus engine and a wood fire have quite different impacts by age, general health, local temperature, humidity etc. We are back to making contextual assessments.

If we are making a specific claim about a reduction in a exposure to a specific particle type, we need to know the context in which this takes place. There are several woods in Africa that will kill you if you breathe the smoke or eat food roasted over it. Not all wood smoke is alike.

If tiers are to be set for stove emissions rates and health benefits are to be claimed for them, then the rates have to apply to actual species and actual exposure. This is already done for smoked fish, in case anyone needs a convincing analogy. Smoked fish are tested for specific contaminants, PAH(4) or PAH(7) for example, and limits are set for ‘exposure’ on the assumption that the whole fish will be eaten. Improving the product quality reduces risk, specifically for the consumer.

The only difference between smoked fish and stoves is that we assume, reasonably, that instead of everything, only a % of the stove emissions will be breathed by any individual. When it comes to PM2.5, it is not enough to say breathed without also saying what was breathed.

Harold, I would appreciate your comments on the nature of this division of risk into a) population risks from all sources and b) an individual’s risk from exposure to particular contaminants. I hope I have captured it correctly. Still learning.

If we can correctly describe the problem, we can proposed solutions. If a stove burns the same fuel and creates a lower PM emission rate and the particles are themselves relatively benign, that can be factored into a relative risk calculation with some medical justification.

Thanks
Crispin
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