Measuring black carbon density
Airborne particles will appear as a spot on the tissue filter. Spots are generally either brown or gray in color. Brown spots are normally caused by dust particles . The dust has a minimal affect on the analysis. The gray is caused by soot (suspended carbon particles). Because carbon is intensely black, it may be detected in small amounts. Compare the sample to the visual scale shown here.
Using the 'Attenuation' scale:
Note that 'Attenuation' = 100 ln ( [blank] / [spot] ),
where [blank] = milliampere reading of the white area of the filter and
[spot] = milliampere reading of the pollution spot collected. Use natural logarithm (ln).
Black Carbon Density = Attenuation / 12
The units of this are micrograms per square centimeter.
Total micrograms of black carbon
in the spot sample = Density x Area of the original collection spot (cm2)
Total sampled volume of air = Flow Rate x Sample Duration
Concentration of Black Carbon in the Air
(in micrograms per cubic meter of air) = Total Micrograms / Total Volume
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