The high charge fraction of flame-generated particles in the size range below 3 nm measured by enhanced particle detectors

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• 作者：Yang Wang^a ; Juha Kangasluoma^b ; Michel Attoui^b ; ^c ; Jiaxi Fang^a ; Heikki Junninen^b ; Markku Kulmala^b ; Tuukka Petä ; jä ; ^b ; Pratim Biswas^a ; ^{pbiswas@wustl.edu} ; ^{pratim.biswas@wustl.edu}
• 关键词：Flame synthesis ; Charge fraction ; Sub-3  ; nm particle ; Titanium dioxide ; Differential mobility analyzer ; Mass spectrometry
• 刊名：Combustion and Flame
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：176
• 期：Complete
• 页码：72-80
• 全文大小：2003 K
• 卷排序：176

文摘

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.