I need to convert particle numbers from particle counter given in bins 0.3-0.5 and 0.5-1.0um to PM 1. What average particle diameter should be assumed for each bin?
Thanks
Miron
Miron Kaliszewski You have or will find that the number and spacing of the class widths has a marked effect on the calculated averages. The recommendation in ISO9276-2 is a log x (size) axis. Thus the mid-point of your size classes should be a log average. On this basis the log average mid-point for 0.3 to 0.5 microns is ~ 0.387 microns and for 0.5 - 1.0 is ~ 0.707 microns. This is easily accomplished in Excel. See attached.
What Alan F Rawle suggested is the right way . However, be aware that if you have just 2 bins in your histogram, the accuracy of the suggested calculation is quite low, reflecting in a somewhat too large error bar in the computed average mass. The problem can be faced performing more accurate particle size measurements so to increase the number of bins in the claimed range, which is 0.3-1 um in your case. the larger the number of size classes in the distribution (within a fixed size grand interval), the shorter the error bar of the mass average, i.e. the better and more useful the result
Miron Kaliszewski
The other point to be aware of is that any error in the number measurement is increased 3-fold in the conversion to mass or volume (as mass & volume are proportional to d^3).
Thank you for the explanation. It is very useful. Perfect! Best regards
Miron
Miron Kaliszewski
It is usual on RG to recommend any answer that is useful for you. I have seen a 'Yes' response with 23 recommendations...
Dear Alan F Rawle, good hint! People tend to "forget" this rather often...
All previous answers to this question are useful to make such a calculation. But let’s not forget two important aspects:
1) Your particle counter has a lower cut-off size of 0.3 microns, so it doesn’t even detect particles below that size. So you really need to consider what you are measuring. Ambient air, combustion sources, tobacco smoke, etc. typically have modes of their particle number size distribution between 50 to 200 nm. Your particle counter wouldn’t even see these particles!
2) From the two channels and the size of the bins I would expect your particle counter to be a cleanroom device. These counters are designed to measure very low concentrations. If you use them outside a cleanroom they will quickly go into saturation and effects like coincidence will ruin the measurement.
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