Photoacoustic Determination of Absorption Coefficients for Airborne Particulates Collected on Teflon Filters

In transmission spectroscopy, the absorptivity (or absorption coefficient) of a substance is defined as a = A/bc, where A is the absorbance, b the path-length of light through a sample, and c the concentration of absorbing material in the sample cell. The absorbance is defined by A = log Io/(Io-Ia) with Io representing the intensity of the unattenuated light beam and Ia the intensity of the absorbed light. In photoacoustic spectroscopy (PAS), Ia corresponds to the signal from a given sample, S, and Io to the signal from a black body reference with identical thermal properties, R. The PAS analog to absorbance, Apas, can therefore be written as in equation 1.