Spectrothermography of carbonaceous particles

Spectrothermography, defined as the evaluation of thermograms of carbon evolved from heated aerosol samples, is a technique for evaluating differences in particle characteristics as they relate to emission sources and processes that modify particle evolution. Here we describe the inherent uncertainties and demonstrate the utility of this technique with an evaluation of samples that were collected with eight stage cascade impactors at three sites in Mexico City over a period of 5 months. The study was implemented with statistical analysis based on tests for goodness of fit to separate thermograms with distinctive shapes related to the relative amounts of organic and elemental carbon mass that evolves as a function of temperature. Thermograms with unique shapes were found for particles with aerodynamic diameters of 1-10, 0.56-1, 0.32-0.56 and 0.18-0.32 mu m with further differentiation of curves related to the relative amounts of gasoline and diesel fuel that was combusted in the region of the three sites. The common shapes fit 32-42% of samples in each particle size range and indicate that this type of analysis can help distinguish differences in the primary sources of organic and elemental carbon.