INFORMATION RELEASE 2107-22

 

AS1807:2021 and AS/ISO14644-3:2021 standards concerning aerosol photometers and their calibration requirements.

 

Changes to AS1807 released in 2021 SPECIFICALLY related to the use of Aerosol Photometers for various tests require changes to the operation and calibration of those instruments to meet the new requirements.

 

There are other changes to the mentioned standard you probably should be aware of, but we do not discuss them in this document. We suggest that you have a good read of this new standard and have it to hand for reference. The change we are focusing on is the new requirement to measure and record the upstream concentration in gravimetric units (μg/L), sections 4.4.5.2 c) and 4.4.7 d). The standard is slightly confusing by defining concentration in two ways which are the same (100 μg/L = 100mg/m³).

 

It is important to understand that:The "Aerosol Photometer" as we know it today was never designed or intended to be used as a gravimetric measure. This instrument measures and reports "% light scattering" referenced to a “100% reference". So far, we can trace its origins to 1922 (NYO-512 – “Studies of filtration of monodisperse aerosols” by Victor K. La Mer), STILL using the same optical design from before 1945 when it was called a "Light Meter". It is technically more accurately called a "Nephelometer" and best described by Thermo Systems Report back in 1971, see below:

 

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Over 12 months research has resulted in a new calibration system - GraviCal - which can produce a gravimetrically calibrated source of polyalphaolefin (PAO4) with a controllable concentration range from 1μg/L to more than 110μg/L. We are currently working on calibrating the lower ranges, but this is difficult with standard laboratory equipment.

 

 

 

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We have assessed most brands of "Aerosol Photometers" and have found none to be linear to the balance (µg/L) which is a known issue when a quantity is measured indirectly (refer to “D. Conclusions” bottom page 1).

 

An example of the “Calibration Graph” to be supplied by Fotometrix Pty Ltd as part of the new calibration report is shown below:

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Using the calibration graph above, the operator can determine the gravimetric concentration from the photometer display when the instrument is has been gravimetrically calibrated. For traceability purposes, we recommend, recording the instrument meter reading as well as the upstream concentration mix required by the standard.

 

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​Should you have any questions or require further assistance, please email us.

 

Thank you for your interest,

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Since 1987, the specialists in calibration of particle counters and aerosol photometers.

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