[Stoves] PM measurement with Speck

[Frank Shields]

Dear Crispin, Stovers,

<snip>

First wondering what is the basis for separating particles in the < 2.5um? When I was testing air sample for asbestos they used 5um and 2.5um (if I am remembering correctly) as that was the range of size they found in lungs. So, I believe that was actual size measured and so the test method actually measured the size of particles in the air (on a filter paper) under a microscope. 


But in this case you are measuring particles from reflected light. Therefore the size that was determined to be the problem must have been determined by comparing households with health issues (associated with air contamination) TO houses having dust particles determined via reflected light to have a higher percentage of that range of sizes. Is that correct?

As I see it:
1) If the above statement is true there is no need to attempt to a mass measurement. That just creates unnecessary error. 

2) If mass of dust per unit volume was the measure when comparing to houses with health issues it seems that is really the only way to test. A filter paper mass increase after a volume of air is delivered. Trying to go from reflected light to mass is introducing lots of error. 

3) I am thinking a better test is as follows:  This idea is taken from the Silt Density Index test for water - but modified for air. PDF Silt Density Index Standard Test Method <http://www.hanthony.com/aes/Library/SDI.pdf>

Thinking the smoke effects the lungs by plastering and clogging the lungs with surface particles.  Could be effected more by tars and flat shaped than weight or size - but likely a combination of all. 


Procedure: 

>>> air intake >>> filter paper >>> air flow gauge >>>  vacuum gauge  >>>  Vacuum pump >>>  air out flow >>>

a) We set the vacuum gauge to be constant through out the experiment. 
b) We monitor the flow gauge and conclude the experiment when the flow drops below a certain reading OR a specified volume of air has passed through the system.
c) The TIME it takes to reach the specified reduced air flow OR the MEASURE of reduced air flow once the specified volume of air has passed  >>  computes the final result of the test. 

I think this test is very simple with cheap equipment. It more reproduces what is happening in the lungs. 



Thanks

Frank


>> 
>> What is the converting factor going from reflected light to mass? 
> 
> The measure the area of the reflected dot and convert it to a circle and
> estimate the volume of a similar sized globe. A density is found practice
> and calculation. Wood fire particles have a density of about 1.00.  If
> someone says it is different, make them prove it. You can assume PM5-PM10
> particles are 2.5 or 2.3. 
> 
> Wood fires don't make large particles unless there is a fan, but even then,
> they are about PM4-5. I can show you the difference of fan-on and fan-off if
> you really want to see it.  I have data from a fan stove. Then it is on low
> and high is clearly visible. With no fan (low power) it looks just like the
> distribution of a natural draft fire which is all below PM1 and most below
> PM0.6.
> 
>> When the reported value is 2.5 um is there a range like from 3um to 2um and
> above and below that not included?
> 
> All PM numbers include 'everything smaller'.
> You can divide the measurements into any ranges you want but you need a
> machine like a Grimm 11-R or 11-C to do that. There is a Grimm 320 that the
> SeTAR Centre has which will do 31 bins from PM0.22 to PM100.  The Grimms
> have the big advantage of having size selectable brackets of your own
> choosing. So you can shift the available 31 slots into regions of interest
> and see quite fine divisions if you want. There is a tab for putting in the
> sizes you want counted in each channel - they can even overlap I think. 
> 
>> Is the angle of reflected light used to determine the size of the
> particles? 
> 
> No. I think the angle is used when working with particle physics to
> determine mass directly, not so?
> 
> Another method is static attraction to one side. The particles are sped
> through a portal at a known velocity and charged. A plat on the side is
> divided into separate landing zones. If the particles are light, they swing
> to the side quickly to the first landing zone. Heavier particles land
> further on. The nanoparticles can be grown by condensing vapour on them and
> detected in that way, with the growth known very accurately. The mass of the
> condensation is deducted and the balance is the nanoparticle.
> 
> The new Grimm technology is not like that.
> 
> A Tapered Element Oscillating Microbalance is a filter mounted on the end of
> a vibrating beam. The sample is drawn through the filter and its mass change
> moves the vibrating frequency. This gives real time mass. By using a cyclone
> a particular size (like <2.5) the mass of that fraction can be watched.
> Fortunately for wood stoves, without fans anyway, there is no need to use a
> cyclone because there are virtually no particles larger than PM1.0 so you
> get PM2.5 automatically. This also affects the sampling. If the sample is
> well mixed and not blasting down a tunnel, you don't have to have isokinetic
> sampling either. That saves a lot of complexity and checking. 
> 
> If you use a SeTAR type diluter where there is no 'blow-by' in the tunnel,
> the whole sample is taken into the instrument so there is no influence in
> terms of kinetics. There is a letter somewhere explaining all this to the
> JICA Team in Mongolia. It is possible to use particular aspects of wood or
> coal combustion to eliminate a lot of the complexity in PM measurement that
> is assumed to be necessary in EPA methodologies. Power stations and outdoor
> are sources very different from stoves.
> 
> Regards
> Crispin
> 
> 
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