Noise Characteristics of an Instrumental Particle Absorbance Technique

Noise characteristics and noise reduction techniques for the particle soot absorption spectrometer (PSAP) are discussed. It is shown through elementary propagation of errors analysis and verified through simulations and by experiments that the PSAP signal noise varies as the −3/2 power of the integration time and not the assumed −1/2. It is also shown that neither simple boxcar averaging of independent absorptivity values nor the commonly used moving boxcar average allow realization of the maximum signal to noise ratio. Instead it is argued that maximal noise reduction is realized by post-processing of the raw reference and sample channel intensities. Finally the implications of these findings are demonstrated with representative field data.