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</o:shapelayout></xml><![endif]--></head><body lang=EN-CA link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Dear Friends<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I know this is a matter of limited interest but this list is the right place to share the information.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><u>The direct and indirect radiative effects of biogenic secondary<o:p></o:p></u></p><p class=MsoNormal><u>organic aerosol<o:p></o:p></u></p><p class=MsoNormal><a href="http://www.atmos-chem-phys.net/14/447/2014/acp-14-447-2014.pdf">http://www.atmos-chem-phys.net/14/447/2014/acp-14-447-2014.pdf</a><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>This paper discusses naturally occurring biogenic secondary organic<o:p></o:p></p><p class=MsoNormal>Aerosol from trees (etc) which form part of the background PM2.5. There are two major contaminants that mess with the PM numbers measured when testing stoves – water vapour (when the humidity is about 70%) and ‘other things’ like ground-blown dust, smoke from other sources and natural haze from (especially) trees. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>It cites papers works by two Stove listers Tami Bond and Harold Annegarn.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Some stoves are <i>so</i> clean that the background level dominates the readings. Establishing what the background level is becomes very important. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The condensation of water vapour is a serious issue in hood collection systems and according to TSI (the instrument people) the effect is significant above 70% humidity which is a lot lower than my uneducated guess. Using ambient air as a dilutant for PM is the main problem. If the air has more particles in it than the stove is emitting, how can you tell what the stove emissions are? That is the basic idea. If you are using ambient air in a hood, the condensation of water vapour (which is not what we want to measure) can completely overwhelm the PM emissions from the fire.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Stoves produce a <i>lot</i> of water vapour from fuel moisture and burning hydrogen. This easily condenses and is measured as a particle by light scattering instruments. Filters collect everything and you can dry them to remove the moisture but will remove things that evaporate above the dilution tunnel temperature. For example bio-aerosols that condense at 50 or 80 C will also be removed from the filter by drying. The question is what % effect this has on the filter mass. Turns out it depends on where you are: i.e. near forests means more and a larger effect. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Using a filter for end-to-end measurements means there is no real time PM data and it is hard to know when the smoke was produced: during ignition, during high power burning... That makes tuning a stove to super-low emissions difficult. So you see the problem.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The paper above is dealing with Cloud Condensation Nuclei and growing particles – a little arcane for stoves as it focusses on albedo, but it is yet another paper relevant to the PM conversation.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Regards<o:p></o:p></p><p class=MsoNormal>Crispin<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>