An Automated Thermal-Optical Method for the Analysis of Carbonaceous Aerosol

Abstract

An instrument employing both thermal and optical measurements has been developed for the analysis of organic and elemental carbonaceous aerosol collected on glass or quartz fiber filters. The technique involves volatilization of organic carbon from the filter under conditions where the elemental carbon remains. The volatilized carbon is oxidized to CO 2 , reduced to CH 4 , and measured by a flame ionization detector. Elemental carbon is subsequently oxidized to CO 2 and measured. The reflectance of the filter is continuously monitored throughout the analysis by a helium-neon laser system. During the organic analysis some of the organic carbon is pyrolytically converted to elemental carbon; this results in a decrease in the filter reflectance. Correction for the pyrolytic production of elemental carbon is achieved by measuring the amount of elemental carbon oxidation necessary to return the filter reflectance to its initial value. The instrument is completely automated and is under the control of a microprocessor system. It has been evaluated with respect to model compounds, typical source mixtures (e.g., auto exhaust aerosol), and ambient samples. Although carbon has long been recognized as an important constituent of ambient aerosols, the analysis of carbon in its many molecular forms has presented formidable obstacles. An approach taken by many investigators (1-12) has been to separate aerosol carbon into organic, elemental, and carbonate classes. However, at the present time only carbonate carbon has an unequivocal analytical definition. Speciation between organic and elemental car-0097-6156/81/0167-0223$05.00/0