COAGULATION OF CIGARETTE SMOKE PARTICLES

Abstract

Experimental measurements on the deposition of cigarette smoke particles (CSP) in the human airways have produced results that are inconsistent with typical deposition data based on particle size. Previous work relating to hygroscopic growth indicates that hygroscopicity alone can not account for this discrepancy. The present study investigates coagulation of CSP modeled as a polydisperse-charged aerosol as a possible explanation. The results of the model more accurately predict the experimental coagulation data for mainstream CSP than models that treat CSP as a monodisperse or polydisperse-uncharged aerosol. An aerosol with an initial charge distribution based on Boltzmann equilibrium yields slightly larger coagulation rates than the mainstream CSP polydisperse-charged model. The numerical results indicate that the size and charge distribution of sidestream CSP, with a concentration of 10 6 particles cm -3, remain stable. In 2 s, the size distribution of mainstream CSP, with a concentration of 10 9 particles cm -3, shifts to a larger size while becoming flatter and wider. The diameter of average mass increases from 0.29 to 0.5 μm. Numerical results confirm experimental reports for mainstream CSP, which indicate that the total number of charged particles increases with time and, in the early stages of coagulation, the amount of charge per particle cannot be estimated based on the particle size. This study shows that polydisperse-charged CSP, allowed to coagulate for 2 s in the mouth, will not produce size distributions that yield the observed deposition of CSP. However, additional coagulation will take place as the CSP travels through the respiratory tract, which will be investigated in future work.