E-cigarette use is a potential source of particulate matter and chemical exposure in indoor spaces such as cars, homes and offices. A fraction of the aerosol inhaled by the e-cigarette users is exhaled into the space. A computational model has been developed to predict changes in particle size and concentration of chemical constituents over time. The model is based on the thermodynamic vapor/liquid equilibrium for tracking phase partitioning and overall mass balance of each chemical constituent. The results from the first principle model have been validated using published experimental data for machine generated aerosols. The model prediction for the nicotine concentration in the room averaged over 12 runs is within 5% of the experimental value. Further validation will be carried out as data from human studies become available.

Modeling results indicate that the concentration of chemicals drops substantially as the room size and ventilation rate are increased. The results from the model also show that particle size drops rapidly due to evaporation of volatile compounds from the particles. A sensitivity analysis has shown that by increasing the frequency and volume of aerosol release into the room, the concentration of chemicals might reach an upper plateau at low ventilation rate. The model may be used to estimate the indoor level of various chemicals and aerosol concentrations at different release rates, room sizes, air ventilation rates, aerosol compositions, and room and ventilation air temperatures and humidity. It can also be used to compare different devices and/or different liquid formulations in terms of room concentration of chemicals of interest.