[Stoves] [Stoves Digest, Vol 81, Issue 21] Another attack on solid fuels by public health adventurers

[Crispin Pemberton-Pigott]

Dear Karin

I am taking a moment to respond to your message of 27 May. It concerns your very important comment about the reduction in PM and CO. Because it has been a while, I will repeat the relevant paragraph:

“The note that you cited [from] our paper saying that the Philips stove reduces PM2.5 concentration by only 66% was a cite of the work by Muralidharan et al., 2015. It is based [on] a KPT not in a WBT: “Here, we tested a traditional clay chulha cookstove (TCS) and five commercially available ACSs, including both natural draft (Greenway Smart Stove, Envirofit PCS-1) and forced draft stoves (BioLite HomeStove, Philips Woodstove HD4012, and Eco-Chulha XXL), in a test kitchen in a rural village of western India. Compared to the TCS, the ACSs produced significant reductions in particulate matter less than 2.5 µm (PM2.5) and CO concentrations (Envirofit: 22%/16%, Greenway: 24%/42%, BioLite: 40%/35%, Philips: 66%/55% and Eco-Chulha: 61%/42%), which persisted after normalization for fuel consumption or useful energy. PM2.5 and CO concentrations were lower for forced draft stoves than natural draft stoves. Furthermore, the Philips and Eco-Chulha units exhibited higher cooking efficiency than the TCS. Despite significant reductions in concentrations, all ACSs failed to achieve PM2.5 levels that are considered safe by the World Health Organization (ACSs: 277–714 μg/m3 or 11–28 fold higher than the WHO recommendation of 25 μg/m3;)”
Two issues arise from these comments. The first is the idea that the stove is the only or major reason for the PM2.5 concentration measured. Obviously if the stoves had been fitted with chimneys the concentration would have been as low as zero, which is to say, that stoves would have contributed as little as nothing and any measurement would reflect the background level. IF the ambient concentration is 100 then a perfect stove will not help.
Even if the stoves produced varying amounts of smoke, the test was of the influence of that stove in a particular kitchen operated in a certain way by a certain cook producing a certain meal. It was the kitchen that had the largest influence on the concentration.  I acknowledge that there is value to having a relative performance difference, but mostly you were testing the kitchen, not so much the stove, with my concession that the stoves are different as to the amount of smoke emitted.
The numbers reported: are they personal exposures? If so, then people in the same room will be subject to quite different exposures. If it was ‘ambient in the room’ then we do not know what the personal exposure was because it depends on where you are in the room. Ambient at head height varies around the room.  As the WHO has reported in their meeting minutes, the concentration in a room is highly variable depending on the ventilation rate and the position of vents. In spite of that knowledge, they assume (at present) that the concentration is immediately equal through the volume of the room which is obviously unrealistic.
My second point the idea that, somehow, the WHO has a justifiable claim that 25 µg/m3 is ‘safe’ or ‘healthy’ with the implication that the number is supported by some evidence. Having looked into the way the value, or ‘target’, was generated, I found there is literally nothing real behind the number. It is all estimations, assumptions and guessing. I don’t think there is much danger this observation will be contradicted.
There are several useful conclusions one can draw from the study.

  1.  Chimneys should be promoted as a way to reducing exposure to smoke by cooks and children as a matter of urgency when the kitchen is enclosed. Whatever the health impact of some emissions from common fuels, chimneys make everything better.
  2.  Where the stove is openly vented, a stove hood is appropriate.
  3.  People cooking outdoors are at very low risk of exposure to cooking smoke, and about ¼ of India’s cooking takes place outside – maybe more. In Indonesia there are 4 classic kitchens only one of which is enclosed.
  4.  Unless it is already in the ambient air, cooking outdoors offers little exposure, and smokeless stoves are rarely, or never, going make a tangible difference. Ulaanbaatar heating stoves are a good example of an exemption to this, but they are heating stoves, primarily. Crakow is another.
  5.  Some weak and unjustified arguments have been made about ambient air pollution from stoves being a major cause of indoor air pollution in other homes ‘because of the use of chimneys’. If this were true in any community, it means that only an integrated air quality program could make a big difference, as is being implement in Hebei Province in China. That pilot includes a heating and cooking stove component (800,000 units) with a view to improving ambient air quality in Beijing, next door. But it is one of 51 measures being conducted. Getting the smoke outdoors by hood or chimney where it can be greatly diluted is obviously a good start.
The current discussion here and behind the scenes is concentrating on the main flaws in the WHO’s case for claiming what constitutes a healthy environment:

Flaws:

  *   The assumption that all particles below 2.5 microns in aerodynamic diameter are equally toxic
  *   That a certain list of diseases are caused by a certain exposure to PM2.5
  *   That a certain list of diseases are exacerbated by a certain exposure to PM2.5
  *   That certain diseases are caused by exposure to particular sources
  *   That an ambient concentration causes a certain exposure
  *   That a certain emission rate creates a certain ambient concentration
  *   That the smoke emitted by a stove can be meaningfully reported as an ‘emission rate’ without reference to constancy (pulses) and independent of time.



We need a reboot on this whole matter. There are far too many things assumed being given the status of ‘truth’.  I suggest the main reason for the reboot is because there is a lot of money being directed, or redirected, based on really poor quality information and guesses. I appreciate that you are making measurements and creating a base upon which to construct a more realistic version of reality.



Regards

Crispin


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