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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoPlainText>Dear Julien<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Thanks for the explanations. As it is clearly a subject at the early stage of investigation we will expect to hear a great deal more on the subject.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>>The cookstoves they tested were (1) a 3-stone fire, and (2) the “Chulika” rocket stove (distributed by iSquareD, Bangalore, India), both burning sticks of hemlock; and (3) the fan-powered “Oorja,” TLUD stove (First Energy Ltd., Bangalore, India) burning commercial wood pellets<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText><span style='color:black'>The fan stoves have the ability to loft a lot of ash so it is not a surprise to see the emission profile change. So far I have found that there is very little ash (evidenced by larger particles) in natural draft stoves, even those with 3 metres of chimney. Wood and coal ash can be quite fine so it is easy to get airborne. When there is no stirring of the fire which shakes ash into the gas stream, the particle size is usually 99% <1.0 µm.<o:p></o:p></span></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>>> Something that is not clear from the abstract is whether the <o:p></o:p></p><p class=MsoPlainText>>> 'increase' in particles is an increase in the number of particles or <o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>>Number of particles. Over a range of 15 to 660 nm particle diameter, they measure the number of particles per unit volume of air, as a proportion of the mass of carbon emitted …<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>I see two potential problems with this. The first is that stove often make char these days and the amount of carbon detected is not a true indication of the amount of fuel burned. It is one of the reasons the SeTAR <i>HTP</i> uses a chemically balanced approach to calculations rather than a Carbon Balance one. The second problem is whether it has been shown that the number of particles is more important than the mass, epidemiologically speaking. They have to report something but it is interesting to watch both counts, as it were.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>>…but there was a decrease in the size of particles emitted.<o:p></o:p></p><p class=MsoPlainText><span style='color:black'><o:p> </o:p></span></p><p class=MsoPlainText><span style='color:black'>The most likely reason is that the stove is producing gas and burning it – in other words it is staged combustion. This is well known and it not restricted to TLUDs or any particular stove type, though it is clear that open fires and sheltered fires (like the Rocket) are basically the same in their combustion method. Where there is a clear separation within the combustion zone(s) between solid fuels and burnable gases, there are far fewer particles. This is really easy to demonstrate with coal stoves. All coal fires are gas fires. The only way to get significant PM from it is to evaporate something liquid and then cool it without combustion. It is a PIC (particle of incomplete combustion) not a product of the gas fire. A very simple measure to prevent the PIC’s from ‘getting away’ in a Mongolia traditional stove is to put in a ‘flame tube’ where all flame and smoke and CO are bought together at the rear of the stove. This simple addition (taught as a retro-fit) reduced PM about 80% and cost only $1 for a stainless steel tube (from a milk pipe supply shop).<o:p></o:p></span></p><p class=MsoPlainText><span style='color:black'><o:p> </o:p></span></p><p class=MsoPlainText>>The increase in efficiency is good, because there is less fuel used (fewer trees cut, less time gathering wood, less time cooking and attending the stove), and a lower total mass of particles emitted.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>We have to be really clear what is meant by ‘increased efficiency. The reason, at this time, for such caution is that the CDM credit system attributes fuels savings indirectly, on the basis of a change in the heat transfer efficiency. With char making stoves – now gaining popularity at least among enthusiasts, there can be a large increase in heat transfer efficiency (because of burning gas in close proximity to the pot) while not reducing the fuel consumption at all. We are very clear at the CSI project in Indonesia that the meaning of ‘efficiency’ is ‘system efficiency’. System efficiency is defined in terms of the potential energy available in the fuel provided, and the % of that which gets into one or more pots. <o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>This does not raise the question of combustion efficiency v.s. heat transfer efficiency. One can make more PM (in a different spectrum) while increasing the heat transfer efficiency.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>>…When all trade-offs are considered, a better nutrition and quality of life may come from using improved cookstoves, even though they may pose a new set of health risks down the line.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Using a chimney or hood almost always makes a big improvement to the kitchen air quality.<o:p></o:p></p><p class=MsoPlainText><span style='color:black'><o:p> </o:p></span></p><p class=MsoPlainText>>That is an interesting point that there is a natural background of untrafine particles. <o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Burning grass and forests create vast amounts of PM of all sizes. Cool fires with damp grass are particularly ‘productive’. I think the brown cloud of India is more because of biomass burning in the fields than from cooking fires.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Huge areas of Africa are burned each year as part of the grazing cycle. Many plants require fire each year to survive. We may have a remarkable tolerance to UFP’s but I see no guarantee of it. Perhaps we are and have been sick for centuries! At least we can eliminate the ones we produce deliberately.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Regards<o:p></o:p></p><p class=MsoPlainText>Crispin<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p></div></body></html>