Particle Size Distribution of Mainstream Cigarette Smoke Undergoing Dilution

Abstract

Mainstream cigarette smoke generated using an automatic smoking machine (SEM-II) and Kentucky 2R1 reference cigarettes was analyzed for particle number concentration and size distribution. About 90% of the smoke was sampled with an Andersen Cascade Impactor after primary dilution (6-, 10-, or 18-fold). The remainder was further diluted 13,600- to 79,000-fold before analysis with an Electrical Aerosol Analyzer and Condensation Nuclei Counter. The primary dilution ratio and compositions of the dilution streams (nitrogen, laboratory air, dry air, or the vapor phase from filtered smoke) were varied in the experiments. Reliability of the experimental system was checked using NaCl aerosols. The composition of the dilution stream did not significantly affect the size distribution of the cigarette smoke for a given primary dilution ratio. The volume distribution was bimodal, with median diameters for the two modes of about 0.25 and 5 μm. The number concentration was typically 10⁹ particles /cm³, and the supermicron particles contained 5 to 30% of the total volume. Increased particle evaporation occurred when the primary dilution ratio was increased from 6 to 18. Total particulate matter (TPM), calculated from the size distributions, agreed reasonably well with Cambridge filter measurements. Previously reported data were shown to be reasonably consistent when the equivalent TPM was calculated from the size data.