Monitor calibration

Technical questions that one would like posed to experts
(scientists) in fields related to particulate pollution.

Monitor calibration

Postby swiper » Thu Jan 28, 2010 6:15 am

Is there such a thing as a standard 'smoke' available for checking or calibrating particle meters in the PM2.5 and Pm10 ranges?
Thanks.
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Re: Monitor calibration

Postby Wilberforce » Sat Jan 30, 2010 6:59 pm

I don't know exactly what procedure they use to calibrate PM meters, but I do recall
a lab experiment from college. A micromolar mass of the chemical Ammonium Chloride
(NH4Cl) can be carefully measured out and heated (it smokes via decomposition and
sublimation) If this is done within a large pyrex vessel of known volume (say a 10 liter
flask) the mass per unit volume, and particle count can be determined. Of course (A)
all of the powder must sublimate and (B) the vessel walls must be kept very hot so as
absolutely no condensation takes place on interior vessel surfaces.

For example, if one µg of NH4Cl is completely sublimated within a volume of 0.01 m3
vessel, we have a calibration point of 100 µg /m3 of airborne micro particulate.

The problem lies in the accurate measurement of vanishingly small amounts of test reagent.
It might be better (but less accurate) to vaporise one gram into a large room of 10,000 m3
(33m X 33m X 10m) a very large room indeed. But then uniform dispersion may become a
problem, as would condensation and fugitive vapor escaping out of the seams of the enclosure.

At any rate, this is a good topic to discuss. The Dylos instrument which I've purchased is
factory-calibrated, but it would be nice to routinely verify that calibration, and compare to
U.S. standards of particle mass.
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Re: Monitor calibration

Postby swiper » Tue Feb 02, 2010 4:08 am

Thank you.
Yes it would appear that monitors should be checked annually for calibration, and this is usually done by comparing them with a 'known good.' The trouble is, if the reference unit is out they are all out.
At some stage I take it, there must be a standard calibration performed. I wonder if Dylos would explain how they do it?
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Re: Monitor calibration

Postby Wilberforce » Tue Feb 02, 2010 9:04 am

That's a good try. I had spoken with the company owner when I bought my unit, but did not think
to ask how they calibrate. This man (can't recall his name) is a good businessman who would be glad
to explain the process, (or refer you to an in-house tech who can.) Especially while you are in the
process of buying (or have previously bought)
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