Black carbon (BC) aerosols strongly absorb sunlight and affect earth's radiation budget by so called direct effect. In addition to mass loading, size distributions and amount of coatings on BC particle are necessary to quantify radiative effects of BC in atmosphere. In contrast to these demands from atmospheric science, majority of traditional methods to measure BC are based on its ensemble properties (e.g., mass concentration) neglecting its distribution in size and mixing states. The single-particle measurements are superior to the ensemble-particle measurements in its physical reasoning of the measured quantity, detection limit, and time resolution. Recently, principles of laser-induced incandescence (LII) technique have been applied to single-particle measurements of BC. Single-Particle Soot Photometer (SP2) is the first commercially available instrument for single-particle measurements of BC by the LII technique.

The author characterizes responses of the SP2 to internally mixed BC by using newly developed experimental setup and a theoretical model. Based on the experiment, LII signals measured by SP2 were found to be not affected by the amount of coating on BC, demonstrating that intensity LII signals only depends on amount of BC in individual particles. Based on numerical experiments using the theoretical model, time-dependent intensities of LII and light-scattering signals for internally mixed BC were assigned to the changes of particle temperature and diameter during laser irradiation, elucidating physical reasons of signal waveforms measured by the SP2.

The author developed a new method to measure time-dependent scattering cross section of particles evaporating in a laser beam. This method is based on the principle of that the rate of change (R.C.) of scattering signal can be decomposed to the R.C. of incident laser irradiance and R.C. of scattering cross section of the irradiated particle. The author demonstrates that light-scattering sizes of individual BC particles can be measured by an application of the new method to SP2 measurements. For individual internally mixed BC particles, size of BC core and amount of coating on BC can simultaneously be measured by a combination of the new method and the LII technique.

Aircraft observations of BC using the SP2 were conducted over the western Pacific in March 2004. During ~ 16 hours transport of urban plumes, significant evolutions of size distribution of BC and amount of coating on BC were observed.