"Direct Dripping": A High-Temperature, High-Formaldehyde Emission Electronic Cigarette Use Method

Nicotine Tob Res. 2016 Apr;18(4):453-9. doi: 10.1093/ntr/ntv080. Epub 2015 Apr 11.


Introduction: Electronic cigarettes (ECIGs) electrically heat and vaporize a liquid solution to produce an inhalable nicotine-containing aerosol. Normally the electrical heater is fed the liquid via an automatic wick system. Some ECIG users, however, elect to directly drip liquid onto an exposed heater coil, reportedly for greater vapor production and throat hit. Use of such "direct drip atomizers" (DDAs) may involve greater exposure to non-nicotine toxicants due to the potentially higher temperatures reached by the coil. In this study we examined nicotine and volatile aldehyde (VA) emissions from one type of DDA under various use scenarios, and measured heater temperature.

Methods: Aerosols were machine-generated from an NHALER 510 Atomizer powered by an eGo-T battery (Joyetech), using a common PG-based liquid and a fixed puffing regimen. Inter-drip interval, the number of puffs drawn between replenishing the liquid on the coil, was varied from 2-4 puffs/drip. Total particulate matter, nicotine, and VA yields were quantified. Heater temperature was monitored using an infrared camera.

Results: Depending on the condition, VA emissions, including formaldehyde, greatly exceeded values previously reported for conventional ECIGs and combustible cigarettes, both per puff and per unit of nicotine yield. Increasing the inter-drip interval resulted in greater VA emissions, and lower total particulate matter and nicotine yields. Maximum heater coil temperature ranged from 130°C to more than 350°C.

Conclusions: Due to the higher temperatures attained, DDAs are inherently likely to produce high toxicant emissions. The diversity of ECIG use methods, including potential off-label methods, should be considered as ECIG regulatory efforts proceed.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aerosols / administration & dosage
  • Aerosols / adverse effects
  • Drug Delivery Systems / methods
  • Electronic Nicotine Delivery Systems / adverse effects
  • Electronic Nicotine Delivery Systems / methods*
  • Formaldehyde / administration & dosage*
  • Formaldehyde / adverse effects
  • Hazardous Substances / administration & dosage
  • Hazardous Substances / adverse effects
  • Hot Temperature* / adverse effects
  • Nebulizers and Vaporizers*
  • Nicotine / administration & dosage*
  • Nicotine / adverse effects
  • Particulate Matter / administration & dosage
  • Particulate Matter / adverse effects
  • Smoking / adverse effects
  • Temperature


  • Aerosols
  • Hazardous Substances
  • Particulate Matter
  • Formaldehyde
  • Nicotine