MAGEE Scientific Aethalometer AE33 User Manual page 134

Aethalometer
Model AE33
The London data show a systematic reduction at increasing loadings; while the Boston data do
not. This demonstrates that any method intended to compensate for the 'spot loading effect'
must be auto-adaptive and able to adjust dynamically to different situations. An instrument
based on firmware with a fixed 'loading non-linearity' parameter will not operate correctly at
all locations. The 'loading non-linearity' parameter must be measured.
It is clear that the effect, when present, is linear with loading ('ATN'). This can be represented
as
BC (reported) = BC (zero loading) * { 1 - k • ATN }
where BC (zero loading) is the desired ambient BC value that would be obtained in the absence
of any loading effect; and k is the 'loading compensation parameter' (similar to Virkkula, 2007).
The analysis of a large number of datasets from a wide variety of locations shows that this
relationship is linear in all cases studied; but with different values of k. It is therefore possible
to eliminate the 'loading effect' of k by making two simultaneous identical measurements BC1
and BC2 at different degrees of loading ATN1 and ATN2.
BC1 = BC * { 1 - k • ATN1 }
BC2 = BC * { 1 - k • ATN2 }
From these two linear equations we may calculate the 'loading compensation parameter' k; and
the desired value of BC compensated back to zero loading.
The Aethalometer Model AE33 Aethalometer Model AE33 analyzes the Black Carbon
component of aerosols on two parallel spots drawn from the same input stream, but collected
at different rates of accumulation, i.e. at different values of ATN. By combining the data
according to the above equations, the AE33 yields the value of BC extrapolated back to 'zero
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User's manual – Ver. 1.55 July 2017 134/146