In Situ Light Scattering Measurements of Mainstream and Sidestream Cigarette Smoke

ABSTRACT

This paper presents in situ and continuous size measurements for submicron cigarette smoke particles. The method, which can be applied to any ensemble of small particles narrowly distributed in size, uses the light scattered from the particles at angles of 60° and 120° and the ratio of polarization components of the scattered light at 55° to determine the mean particle size. Polystyrene latex spheres diluted in distilled water are used to calibrate the system. Good agreement exists between the experimental measurements and the theoretical calculations for the calibration particles. Based on the assumption that cigarette smoke particles cluster into locally uniform parcels during their formation as condensate, the light scattering system is employed to measure the mean size and size fluctuations of mainstream smoke and sidestream smoke from research cigarettes (1R3 and 1R3f). Similar light scattering techniques have been employed by other researchers, but this paper describes in situ measurements of smoke without aging or dilution. These in situ measurements characterize the spatial inhomogeneity of cigarette smoke, and show that sidestream smoke is approximately 0.27 μm in count median diameter (CMD) with a geometric standard deviation (GSD) of 1.60 and that mainstream smoke has a CMD of approximately 0.15 μm with a GSD of 2.0. The corresponding mass median diameters are approximately 0.50 and 0.70 μm, respectively. Interestingly, there is little difference in the mean size of sidestream smoke fresh from the tip of a smoldering cigarette and sidestream smoke captured in a vessel. There are differences, however, in the clustering of the smoke and in its nonuniformity. Fresh sidestream smoke exhibits more size fluctuation, but less fluctuation in local particle number density when compared to captured sidestream smoke. The measurements also indicate little difference between mainstream smoke from cigarettes with and without filters. Based on the assumption that the smoke partitions into small parcels with relatively narrow size distributions within parcels, the calculated relative number density of fresh sidestream smoke particles is fairly uniform, while the number density fluctuates significantly for mainstream and captured sidestream smoke.