10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Flame Generated Soot Nuclei: The Asymmetries in Collision Charging evidenced by High-Resolution (APi-TOF) Mass Spectrometry
FRANCESCO CARBONE, Manjula Canagaratna, Andrew Lambe, John Jayne, Douglas Worsnop, Alessandro Gomez, Yale University
Abstract Number: 587 Working Group: Combustion
Abstract Flame products were sampled with a horizontal tube probe from a well-characterized, moderately sooting premixed flame of an ethylene/air mixture with a C/O ratio of 0.69. The samples were quickly diluted in a nitrogen stream seeded with bipolar ions generated by a radioactive source. Diluted and partially charged soot nuclei and precursors were analyzed in a mass-to-charge ratio range up to 2000 using a highly sensitive Atmospheric Pressure Interface Time-of-Flight (APi-TOF, Tofwerk AG) Mass Spectrometer. The high mass accuracy and resolving power (in excess of 3000) of the measurements allowed for the accurate determination of the mass defect distributions of the sampled material that relates to its composition and charge distributions. Analyses were performed at several heights above the burner (HAB) of both positively and negatively charged material. Additionally, the type and concentrations of ions seeded in the dilution nitrogen was varied using two different radioactive sources to investigate the effect of collision charging. Results clearly show an asymmetry in the composition and in the collisional charging efficiency of material detected in different polarities. Materials acquiring a positive charge consistently have a larger content of hydrogen and is detected in significantly larger amounts as compared to materials with negative charge. Furthermore, the comparison of results using two different radioactive sources evidenced that the fraction (more properly, ion attachment efficiency) and the composition of detected materials is sensitive to the number and type of ions used for collisional charging. These findings call for a deeper investigation of the collisional charging mechanisms of flame-generated materials in the sub 2nm dimensional range. Clarification of these mechanism would allow for the quantitative determination of composition and concentration of the originally neutral material generated in the flame.