Source Apportionment of Individual Carbonaceous Particles Using14C and Laser Microprobe Mass Spectrometry

Abstract

An exploratory study of laser microprobe mass spectra of individual atmospheric soot particles has been made in search of a potential combustion source tracer index. A tentative “cluster ratio index” (CRI = C4 −/C2 −) has been found and compared with bulk measurements of 14C in a set of ambient samples exhibiting varying impacts from woodburning and motor vehicle exhaust. A CRI-14C calibration curve resulted, and it led to the conclusion that, at the present level of precision, three particles (or agglomerates) of micrometer size or about 3 pg of carbon would be required for discrimination between the two pure sources. Mixture samples, such as those reported here, would require about 40 times as much. Classification of small set of individual particles from the mixed source ambient samples, suggests preservation of carbonaceous source identity at the single particle level.