Analysis of Mixing State of Atmospheric Suspended Single Aerosol Particles using a Tandem Combination of Laser-induced Fluorescence and Incandescence Techniques

A novel real-time measurement system was developed to determine the mixing state of aerosol particles using a tandem combination of laser-induced fluorescence (LIF) and incandescence (LII) techniques. Particles analyzed with fluorescence detection in the first chamber were delivered to the second chamber connected in series for detection of incandescence. We analyzed identical particles using the two methods as judged by the time intervals of detection in the two chambers. This tandem analysis system provides information on the mixing state of fluorescent compounds and black carbon in single particles. We performed ground-based measurement of ambient particles in Tokyo during October 26-29, 2012 using this system. We analyzed 43,881 particles with optical diameters greater than 0.4 mm. The fractions of particles with fluorescent composition, black carbon, and a mixture of both were 14.2%, 2.3%, and 0.3%, respectively, which indicates the presence of internal mixtures of black carbon and fluorescent species in the ambient air for the first time. Mixtures of biological materials (estimated from fluorescence patterns) and black carbon were also detected. The fluorescence patterns of single particles with and without black carbon were almost identical, suggesting that particles with both black carbon and fluorescent composition might be formed by aggregation in ambient air.