The High Charge Fraction of Flame-Generated Particles in the Size Range below 3 nm Measured by Enhanced Particle Detectors


Charging in flames significantly affects the properties of the resultant particles produced because of its influence in almost all stages of particle formation. The charging characteristics of flame-generated sub-3 nm particles were investigated with three enhanced particle detectors including a high resolution differential mobility analyzer (DMA) coupled with an electrometer, a particle size magnifier coupled with a butanol-based condensation particle counter (PSM-bCPC), and an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF). Up to 95% of the flame-generated sub-3 nm particles were charged at a sampling height of 5 mm above the burner, indicating the existence of a strong ionization process in the investigated flame. This high fraction of charged particles contradicts the classical charging theories, which predict < 1% charge fraction for particles below 3 nm. Positively and negatively charged sub-3 nm particles generated from a blank flame were dominated by organic ions and nitrate ions respectively. The flame-generated ions play an important role during titanium dioxide (TiO2) nanoparticle synthesis, as shown by the attachment of nitrate species on Ti-containing particles observed by the APi-TOF. The effects of the sampling height and precursor feed rate were also investigated.


Civil, Architectural and Environmental Engineering


This work is supported by the Solar Energy Research Institute for India and the United States (SERIIUS), funded jointly by the U.S. Department of Energy (Office of Science, Office of Basic Energy Sciences, and Energy Efficiency and Renewable Energy, Solar Energy Technology Program, under Subcontract DE-AC36-08GO28308 to the National Renewable Energy Laboratory, Golden, Colorado) and the Government of India, through the Department of Science and Technology under Subcontract IUSSTF/JCERDC-SERIIUS/2012. The work was also supported by Academy of Finland via Center of Excellence project in Atmospheric Sciences (272041) and European Commission via ACTRIS2 (654109). Y.W. thanks Mr. Adewale Adeosun at Washington University in St. Louis for the helpful discussion.

Keywords and Phrases

Atmospheric pressure; Electric charge; Ions; Mass spectrometers; Mass spectrometry; Nitrates; Oxides; Particle detectors; Particle size; Synthesis (chemical); Titanium dioxide; Charge fractions; Charging characteristics; Condensation particle counters; Differential mobility analyzers; Nanoparticle synthesis; Particle formations; Time-of-flight mass spectrometers; Titanium dioxides (TiO2); Flame synthesis; Anion; Butanol; Nitrate; Titanium dioxide nanoparticle; Article; Atmospheric pressure; Controlled study; Flame; Fractionation; Ionization; Particle size; Polymerization; Priority journal; Synthesis; Time of flight mass spectrometry; Sub-3 nm particle

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version


File Type





© 2017 The Combustion Institute, All rights reserved.

Publication Date

01 Feb 2017