Dependence of Laser-Induced Incandescence on Physical Properties of Black Carbon Aerosols: Measurements and Theoretical Interpretation

Abstract

We used a single-particle soot photometer (SP2) to measure the mass of individual black carbon (BC) particles down to ∼ 0.5 fg by means of laser-induced incandescence with an intra-cavity, continuous-wave laser. The incandescence of nine different types of BC samples was investigated to provide a physical basis for choosing appropriate BC materials for SP2 calibration. We estimated the vaporization temperatures of these BC samples from the spectral dependence of incandescence at the limit of the small size parameter x, for which spectral dependence of emissivity is known a priori. The vaporization temperatures differed by less than 2.2% among the samples. For the x < 1 regime of particle size, the peak amplitude of the incandescence signal measured by the SP2 was linearly proportional to the particle mass. The slopes of such linear proportionality were positively correlated with | (m ² -1)/(m ² +2)|, where the m is the complex refractive index of the BC particle. For particles in which x > 1, the rate of increase in the peak amplitude of the incandescence signal with increasing particle mass was negatively correlated with the compactness of particle shape, consistent with the theoretical prediction of emissivity, which accounts for particle shape. The incandescence–BC mass relationships were similar between fullerene soot and ambient soot sampled in Tokyo, thus suggesting that fullerene soot is a suitable calibration standard for SP2 measurements of ambient soot.

Acknowledgments

We thank Tokai Carbon Inc., Japan for providing TEM images of Tokai glassy carbon particles. This work was supported by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), the strategic international cooperative program of the Japan Science and Technology Agency (JST), and the global environment research fund of the Japanese Ministry of the Environment (B-083).

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Notes

^a ± values are the uncertainties due to the assumption for particle density that was used to derive | (m ²–1)/(m ²+ 2)| values.

^b ± values are the uncertainty associated with the difference in initial particle mass.