[Stoves] benefits from reduced indoor air pollution.

Sat Oct 14 10:02:20 CDT 2017

Dear Andrew

>Firstly is there any reason given for men's higher exposure?

Not that I know of but the final report is not coming out until March.

>Perceived wisdom is that young children were more at risk (at a given level of exposure) as their immune systems were naive  plus presumably their cell divisions are more active and hence open to more chance of disruption.

All very logical. It seems the children gained the most. In particular the occurrence of bronchitis was 25% in the holes with traditional stoves and 0% in the stove-replaced homes. I feel that this was not because of the reduction in smoke but rather that the homes were 5 degrees C warmer. The new stoves are far more efficient and this results in a fuel saving of about 40% and a warmer home. hen people have a large saving of fuel they tend to heat it more, cook more, cook longer and keep food warm - things like that.

I have been very interested in the effect of temperature and how that correlates with disease. It is said that chronic underheating causes far more deaths than either heat waves or worse, cold snaps. Unfortunately we do not have access to the temperature data and disease occurrence yet. It was not our investigation. It will be released eventually, after completing the studies in two other locations where improved stoves were distributed. Apparently they do not show a significant improvement. That is all I know.

>Anyway does anyone think that the recent US EPA step 2 rules for pollutant emissions via chimneys/flues venting outside are at all relevant as a target for stoves?

A serious problem with this topic is the selection inappropriate metrics for making regulations. There are two competing interests: the sharing of a limited airshed, and the quantification of emissions per unit work done. A stove might be rated on the total emissions per hour, or per MJ delivered into the tasks. These are not harmonious options. A stove might be very clean but very large, heating and cooking in a large home.

>They seem to be independent of thermal power  in that they accept 2-2.5 grams particulates per cubic meter irrespective of heat liberated and also susceptible to dilution or have I missed something?

You are missing nothing. The EPA has to choose one method or the other: an emissions rate regardless of the firepower or heating power, alternatively an emission rate per kg fuel, per MJ fire, or MJNET.

I was giving a presentation and lengthy discussion today on this topic. A stove improvement project has been funded in China with the goal of rating performance based on emissions measured in mass concentration of ppm, with an evaluation goal of a net reduction in total emissions. The concentration metrics do not give the total emitted, only how concentrated it is. That is half a formula for the total emissions.

This is quite common.  People copy air quality regulations for large emitters into stove standards without realising that stoves are distributed sources, by definition. So it makes no difference at all what the concentration is, it matters what the volume times concentration is, if the goal is to lower the total. To lower a total you have to have a baseline.

We had a very interesting discussion about NO and its formation, the source of the N in that NO, and the appropriate metric. There are two sources of NO in a stove: fuel N and ambient N2. If the temperature is high enough, NO and NO2 will form from ambient N2, with fuel N have a good chance of making NO.

So, what is the appropriate metric? A carbon balance method cannot be used to create a profile of NO production unless the fuel burns homogeneously, which is almost never. Well, it can be done, but not accurately. Separating the fuel N to NO from air N2 to NO is not possible unless a chemical mass balance method is used. The groups in question only use carbon balance methods so they are stuck right at the starting gate, if they want to trace where the N goes. N, H and O can leave a biomass fuel without burning any carbon at all, so using carbon as an indicator of ‘fuel’ is misleading – by a factor as large as 5.

So the conclusion was that first you have to identify the evaluation criteria, them work backwards to the measurements needed to supply the formula that calculates the total emissions. That informs the nature of the experiment that much be conducted.

By the end, it was clear that lessons learned about large emitters and air quality regulations are not appropriate for small stoves. We will pursue some ideas about the formation of NO on Monday with a larger group. There is a lot of concern about NO, a concern I feel may be over-emphasized because they have been chasing down the wrong metric. No one really knows what the NO mass emitted is.

What is the current EPA target for NO, and how it is calculated?

Regards
Crispin

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