Teledyne Advanced Pollution Instrumentation | Model 633 Aethalometer® Black Carbon Monitor User Manual |
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 Model 633 Aethalometer 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 Model 633 yields the value of BC extrapolated back to ‘zero loading’; as well as a real‐time output of the ‘loading compensation parameter’ k which provides insights into the aerosol nature and composition. This process is performed in real time for all wavelengths: examination of the ‘k’ values as a function of wavelength provides further information about the aerosol composition. An example of this is shown for extreme concentrations of black carbon (Figure 3).
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