[Stoves] Opposition to biomass use in cookstoves.

Wed Jun 26 00:08:10 CDT 2019

Dear Ron

Anytime you see something comparing smoke to smoking, be very skeptical. I managed after a long search to find the origin of the claim (an American writing about China) that tiny amounts of smoke are the equivalent of a large number of cigarettes. I cited the article here on Stoves but don’t have it at hand at the moment. The calculations are laughable. I don’t know how it passed review.

You asked for rebuttals. Here is one for a start:

Assuming a pack to contain 20 standard cigarettes, the claim, “Burning 10 lbs. of wood for one hour releases as many PAHs as 35,000 packs of cigarettes” should be examined.

10 lbs of wood = 4.54 kg = 4536 g, actually.

Tobacco is biomass and a cigarette burns it by smouldering, not burning, so the PAH per g will be much higher than burning wood with flames. Being extremely conservative about the cigarettes and claiming that they are actually equal, and that the PAH content is a similar to that of wood smoke (from all stoves, as they insinuate) the PM emitted by the cigarettes will be:

45 mg/cig x 20 x 35,000 = 31,500,000 mg = 31,500 g of PM from the cigarettes.  That is 7 times the mass of the wood burned.

Indirectly, they claim that burning 10 kg of wood produces 31.7 kg of PM, some fraction of which is PAH. That seems unlikely due to the physical laws governing the conservation of mass.

The additional conceptual error is that wood produces smoke. That website admits on a different page that some stoves produce far less smoke than others. That is true, and contradicts most of their points about the inherency of emissions.  They should correct their pages.

I have previously reported that in the SNV fish smoking project in Ghana we were able to burn red mangrove wood (the traditional fuel) and produce smoked fish with a PAH4 content of 1 part per billion. I have doubts that this could be achieved using smoldering tobacco, and thus doubt the veracity of the assertion that wood is worse.

++++++++++

The following statement cannot be contested as there are no mass concentrations units cited:

“The lifetime cancer risk is 12 times greater for wood smoke compared to an equal volume of secondhand cigarette smoke.”

As the cancer risk from second-hand smoke is assumed, not known, and the content of wood smoke is highly variable depending on species and the stove employed, it is impossible to know for sure if the value “12” is correct or not. If it was, we would see far more deaths from lung cancer in Africa associated with wood smoke inhalation than cigarette smoking, which is not the case.

++++++++++++++

Less defective is the claim, “Toxic free-radical chemicals in wood smoke are biologically active 40 times longer than the free radicals in cigarette smoke”

Maybe.  I’d like to see a study proving it.  Do they mean free-radicals or chemicals?  The imprecision is unnecessary.

Smoke from which stove burning which wood?  As cigarette smoke is burning biomass and so is wood, odds are that there is little difference in the two save the fact that wood is typically burned with a flame and tobacco is typically smouldered with a very high specific emission of PM, including formaldehyde, BC, VOC’s, PAH’s and a host of chemicals (I read once it was ~210 compounds). The claim fails on the grounds of their general assumption that all wood produces the same amount of smoke when burned in all devices. The EPA doesn’t agree. Neither do the States of Oregon and Washington. And Connecticut, and New York, and the UNFCCC.

++++++++++++

 “Wood smoke is unique in containing high concentrations of dioxins and PAHs (polycyclic aromatic hydrocarbons), probably the most toxic components of air pollution.”

I already mentioned PAH and the dramatic manner in which they can be reduced by burning properly. PAH is just unburned fuel and different compounds have very different toxicity levels. Which dioxin? Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) or coplanar polychlorinated biphenyls (cp PCBs)?  Which PAH’s? Benzo-a-pyrene? That’s pretty toxic. It should be under 2 ppb in food imported into the EU.

Wood smoke contains extremely low levels of dioxin (on the order of picograms per cubic metre, i.e. parts per quadrillion) so the claim is probably false.  They could perhaps define “extremely high” in increase understanding.  And, relative to what? It is nearly undetectable. The EPA did<https://cfpub.epa.gov/ncea/dioxin/recordisplay.cfm?deid=254526> find some.

It has been traced in Ontario at 50 parts per trillion in paper made from wood pulp from forests that experienced forest fires. It is a chlorine compound. Biomass contains chlorine so in theory it can be produced. The temperature needed is high. Do all stoves achieve the required temperature and combustion conditions?  Some of them? Any?

If it is TCDD Dioxin it might be the “most toxic” of air pollutants.  I think Frans would disagree and say that plutonium from Chernobyl is more toxic. And 90Sr. And a number of other air pollutants.

+++++++++++

The main problem with the website is it contains claims that are so out of date and inexcusably inaccurate. Wood does not contain any smoke, so burning it and getting some means the stove is responsible. I am convinced the good doctors believe that wood contains smoke and when it is burned, the process releases it into the atmosphere.  They do not believe that smoke is generated by bad combustion. This is a healable knowledge gap. I encourage them to learn more about combustion and why their air quality is what it is.

They would also do well to contact the Masonry Heaters Association and ask how to greatly reduce the air pollution level in wood-burning areas of the USA. Their best typical products already produce lower emissions than the 2022 EPA requirements for wood burning appliances. Instead of condemning a fuel, they should promote the best possible technologies that do so because people are going to burn wood for centuries to come.

Regards
Crispin

(From: Ronal Larson <rongretlarson at comcast.net>
Sent: Wednesday, June 26, 2019 12:12 PM
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>; Crispin Pemberton-Pigott <crispinpigott at outlook.com>
Subject: Opposition to biomass use in cookstoves.

List.  Cc Crispin.  (Changing thread title, since I don’t want to emphasize LPG)

            This is to hope we can have some discussion on the site that Crispin has cited below:  http://woodsmokepollution.org/<https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwoodsmokepollution.org%2F&data=02%7C01%7C%7C01e9392a51be4c29735c08d6f9ec7032%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636971191221508687&sdata=S1eYiCN0XCkAoizFT7KnTZw46HN8NSmb8fOOu%2FK7WUM%3D&reserved=0>.

            I find this site to be extremely well done - and I know of no site that offers a rebuttal.

            In general I agree with Crispin that the site is very critical about biomass use - but there is a huge bibliography to back up their concern on health issues.  I am inclined to agree that some biomass cooking should be outlawed - having been in a few horribly smoky rural homes.   But is this site overcritical.  Are they wrong for not mentioning pyrolysis and carbon capture?

            I doubt anyone on this list could disprove (I hope they will try) any of these four sentences from this cite they give:  https://www.times-standard.com/2017/08/05/burning-firewood-is-an-airborne-public-health-hazard/<https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.times-standard.com%2F2017%2F08%2F05%2Fburning-firewood-is-an-airborne-public-health-hazard%2F&data=02%7C01%7C%7C01e9392a51be4c29735c08d6f9ec7032%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636971191221518692&sdata=fUTxbbyJPOf%2BAIBrwVBxEVOE4Ltt%2BJ8IwpxFyXihP9s%3D&reserved=0>

               -  "Wood smoke is unique in containing high concentrations of dioxins and PAHs (polycyclic aromatic hydrocarbons), probably the most toxic components of air pollution.
          -  Burning 10 lbs. of wood for one hour releases as many PAHs as 35,000 packs of cigarettes.
          -  The lifetime cancer risk is 12 times greater for wood smoke compared to an equal volume of secondhand cigarette smoke.
          -  Toxic free-radical chemicals in wood smoke are biologically active 40 times longer than the free radicals in cigarette smoke"

            So I personally am not trying to make a stove that can negate any of those statistics.  Rather two goals:

                        1.  To make the cleanest possible wood-burning stove - in the belief that, because they are least cost, wood-burning cook stoves will be in use for many years.
                        2.  To make a stove that takes carbon out of the atmosphere - via biochar. (And happens likely to make money while cooking).  That such a stove can save lives - of an unknown amount.   But still likely to never be as safe as some non-biomass forms of cooking.

            I doubt that any  char-making stoves will ever be as clean as the average LPG stove.  (Saying yes- any single LPG stove can be worse - but not on average)  I think this anti-wood site is acting responsibly.  But I wonder if they would agree that our list has merit?   That in many developing countries, there can be no reasonable expectation to stop using wood for cooking?  That there is merit in any technology that can remove atmospheric carbon?

            What are the thoughts of others - on both our site and the way this site is handling our site's issues.

Ron
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