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 CO2, reduced to CH4, and measured by a flame ionization detector. Elemental carbon is subsequently oxidized to CO2 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.