Size-resolved Natural Decay of Environmental Tobacco Smoke Particles in the Unventilated Meeting Room

Particle number concentration (PNC) and particle size distribution (PSD) are two important parameters to access exposure risk of environmental tobacco smoke (ETS) in the unventilated or weakly ventilated meeting room. To investigate the natural decay of ETS, PNCs and PSDs of ETS particles produced by six bands of cigarettes with two levels of tar were measured in the unventilated meeting room with similar temperature and humidity. The characteristics of PNCs and PSDs was slightly different for ETS particles from different types of cigarettes. The decay of PNCs, increase of count median diameter (CMD) and decrease of geometric standard deviation (GSD) were mainly caused by the effects of coagulation. The size-resolved decay coefficients showed a U-shaped distribution as the particle size corresponding to the minimum decay coefficient was about 274 nm. The relationship between half-value periods of PNCs and PNCs was fitted by linear regression of the denary logarithm of half-value periods versus that of PNC. The PSDs of ETS particles from each type of cigarettes followed a lognormal distribution. The relationship between PNCs and CMD was fitted by linear regression of the denary logarithm of PNCs versus CMD, while that between GSD and CMD was fitted by linear regression of GSD versus CMD. The parameters could be simplified from three to one as CMD to quantify the lognormal size distribution of ETS particles. It would be convenient to express PSDs of ETS particles simplified by one parameter in the similar environment.