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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'>Dear AD<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div><p class=MsoNormal><span style='color:#1F497D'>></span>your statement that the smoke might have become invisible due to its being diluted by too much air, admits the fact that there was less smoke per cubic meter of air, which is what all of us are aiming at.<o:p></o:p></p></div></div><div><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>How about this:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Consider a kitchen with an air turnover of 1 cubic metre per minute. You have a stove that emits 5 g of PM2.5 per minute. It creates 1 cubic metre of emissions per minute. The PM2.5 level will stabilise at some level in the room depending on where the air exits, but usually through some point above the stove. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Introduce another stove that has a higher excess air level emitting the same mass of PM per minute but in 2 cubic metres of air. That air cannot leave the room at 1 cu m per minute so it gets distributed further throughout the room. Because air is not moving around to distribute the PM evenly, and never will, the contaminated portion of the room increases, extending further from the stove.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Some of the PM even goes back into the stove – maybe to be burned, who knows? So the result of the lower concentration is not that it helps reduce exposure, it nearly all cases of real kitchens it will increase the general pollution in the room because the room has more ‘stirring’, in a way.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>In order to simulate this the WHO has two models of exposure calculated to give a more realistic result. One is a single box model which assumes all PM is evenly dispersed through the room and everyone in it breathes it. This is obviously far from reality. A second model assumes a three-box approach which models a strong concentration between the stove and the outlet, an upper portion near the ceiling and a lower portion away from the stove. This is more realistic, but does not actually deal with the idea of dilution by circulating more air through the stove – it assumes all stoves have the same amount of excess air passing through. So it is going to misrepresent the exposure as well, but less badly.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>In order to calculate the exposure as a model of reality, the excess air level has to be incorporated into the model to deal with the expansion of the concentrated and upper level boxes into the ‘less polluted’ zone. The EA is not a reported metric so no one knows what the volume of pollutants is, and it cannot be realistically represented by the model.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Generally speaking, reducing the concentration by increasing the gas flow rate through the stove increases the exposure by the cook to PM emitted from a chimney-less stove.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>‘<o:p></o:p></span></p></div></div></body></html>