Direct Exposure Assessment. The median puffs/day by e-cigarette users was assumed to be 175
puffs/day, [2, Etter], with a puff volume of 70 ml/puff, [3, Goniewicz]. The respiratory
absorption of the inhaled vapor was assumed to be 100% for all compounds. We assumed a zero
exposure other than the vapor that was directly inhaled (i.e., no indirect exposure).