Current and previous research findings by this research team are included in this report to address 1) the characteristics of new models of electronic cigarettes and popular customizations; 2) the characteristics of e-liquids purchased over the counter or the internet; and 3) development of a model for the characterization of the particle-size distribution in aerosols. The project determined that fourth-generation e-cig products have evolved to facilitate the aerosolization of drugs from products that are not liquid, but are designed for waxes, dabs, and solid plant materials. E-liquids, semi-solids, and solid materials used in e-cigs can contain dangerous DOTNs, such as synthetic cannabinoids. Evidence indicates that any drug that can be made liquid is being used in e-cigs, including natural products considered "legal highs." The majority of the particles' distribution for nicotine was 0.172-1.0 mm, correlating with deposition in the pulmonary region. Mean particle size of a nicotine aerosol was 0.3 mm, similar to traditional cigarettes. No statistical difference of MMAD and particle-size distribution was found between different common voltages and coil resistances. Methamphetamine and methadone e-liquids generated similar particle-size distribution to nicotine. Methodologies used to obtain these findings are described. 12 figures, 1 table, and a listing of project-related scientific papers, invited talks, and media engagements