Deconstructing ENDS aerosols: generation and characterization methods.

While electronic nicotine delivery systems or ENDS are often marketed as a safer alternative to traditional cigarettes, emissions generated during the operation of these devices contain a complex mixture of toxic substances. ENDS emissions are primarily composed of fine particulate matter (PM2.5, smaller than 2.5 µm in size) and ultrafine particles/nanoparticles (PM0.1, smaller than 100 nm in size), metals (nickel, copper, zinc, tin, lead, and their oxides), carbonyls (formaldehyde, acetaldehyde (a carcinogen), and acrolein), volatile organic compounds (VOCs) (benzene, toluene, and over 70 other VOCs), nicotine, and many unknown chemicals. The levels and composition of these toxic emissions can vary based on factors like device design, e-liquid formulation, device power and temperature levels, and vaping behavior of the user. Within this section of the Special Issue 'Science Education and Research on Vaping and Interventions for Community Engagement', important parameters in defining and characterizing ENDS aerosols will be discussed. Hazardous components of ENDS aerosols including particulate matter, heavy metals, and volatile organic compounds will be delineated and appropriate analytical methods to accurately determine physicochemical properties will be highlighted. Definitions and comparisons of first-hand, second-hand, and third-hand emissions will also be explored alongside pertinent device parameters that influence each type of ENDS emission.