Particle Size Distribution of Mainstream Tobacco and Marijuana Smoke: Analysis Using the Electrical Aerosol Analyzer

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Abstract
Accurate measurement of cigarette smoke particle size distribution is important for estimation of lung deposition. Most prior investigators have reported a mass median diameter (MMD) in the size range of 0.3 to 0.5 .mu.m, with a small geometric standard deviation (GSD), indicating few ultrafine (< 0.1 .mu.m) particles. A few studies, however, have suggested the presence of hultrafine particles by reporting a smaller count median diameter (CMD). Part of this disparity may be due to the inefficiency of previous sizing methods in measuring ultrafine particles. We used an electrical aerosol analyzer (EAA), designed to measure particles in the ultrafine size range, to evaluate size distribution of smoke from standard research cigarettes, commercial filter cigarettes, and from marijuana cigarettes with different .DELTA.9-tetrahydrocannabinol contents. Four 35-cm3, 2-s puffs were generated at 60-s intervals, rapidly diluted, and passed through a charge neutralizer and into a 240-L chamber. Size distribution for six cigarettes of each type was measured, CMD and GSD were determined from a computer-generated log probability plot, and MMD was calculated. The size distribution parameters obtained were similar for all cigarettes tested, with an average CMD of 0.1 .mu.m, and MMD of 0.38 .mu.m, and a GSD of 2.0. The MMD found using the EAA is similar to that previously reported, but the CMD is distinctly smaller and the GSD larger, indicating the presence of many more ultrafine particles. These results may explain the disparity of CMD values found in existing data. Ultrafine particles are of toxicologic importance because their respiratory tract deposition is significantly higher than for particles 0.3 to 0.5 .mu.m and because their large surface area facilitates adsorption and delivery of potentially toxic gases to the lung.