Dept. of Environmental Science
Oregon Graduate Center
A thermal-optical method has been developed for the analysis of organic and elemental carbonaceous aerosol on glass or quartz fiber filters. Organic carbon is volatilized in two steps: at 350Â°C in an 02(2%)-He(helium) mixture and at 600Â°C in He(helium). The volatilized organic carbon is oxidized to C0Â², reduced to CH4, and measured by a flame ionization detector. Elemental carbon is combusted to C0Â² in 02(2%)-He(helium) at 400, 500, and 600Â°C, and the C0Â² is measured as above. The reflectance of the filter segment, which is continuously measured with a He(helium)-Ne laser system, decreases during the organic analysis because of pyrolytic conversion of organic to elemental carbon and increases during the combustion of elemental carbon. Correction for pyrolytic production of elemental carbon is accomplished by measuring the amount of elemental carbon oxidation necessary to return the filter reflectance to the value it had before pyrolysis occurred. This is facilitated by the slow, three-step elemental carbon combustion process. All switching of gas flows, timing, temperature control, pyrolysis correction, analog to digital conversion electronics, electrometer functions, signal integration, data storage and data outputs are controlled by a microprocessor system built around a Motorola 6802 microprocessor. The method has been compared to organic and elemental carbon analyses by the integrating plate method (IPM) and solvent extraction. Good agreement between the thermal-optical method and IPM was found. The solvent extraction method, however, suffered from incomplete extraction of organic carbon. The instrument was used to measure organic and elemental carbon concentrations at a variety of urban and rural sites in the United States and representative examples are given. Both organic and elemental carbon were found to be important components of the ambient aerosol in all samples.
Johnson, Richard Lee, "Development and Evaluation of a Thermal/Optical Method for the Analysis of Carbonaceous Aerosol" (1981). Scholar Archive. 9.