Characterization of combustion-generated carbonaceous nanoparticles by size-dependent ultraviolet laser photoionization.

Photoelectric charging of particles is a powerful tool for online characterization of submicrometer aerosol particles. Indeed photoionization based techniques have high sensitivity and chemical selectivity. Moreover, they yield information on electronic properties of the material and are sensitive to the state of the surface. In the present study the photoionization charging efficiency, i.e., the ratio between the generated positive ions and the corresponding neutral ones, for different classes of flame-generated carbonaceous nanoparticles was measured. The fifth harmonics of a Nd:YAG laser, 213 nm (5.82 eV), was used as an ionization source for the combustion generated nanoparticles, whereas a differential mobility analyzer (DMA) coupled to a Faraday cup electrometer was used for particle classification and detection. Carbonaceous nanoparticles in the nucleation mode, i.e., sizes ranging from 1 to 10 nm, show a photoionization charging efficiency clearly dependent on the flame conditions. In particular, we observed that the richer the flame is, i.e., the higher the equivalent ratio is, the higher the photon charging efficiency is. We hypothesized that such an increase in the photoionization propensity of the carbonaceous nanoparticles from richer flame condition is associated to the presence within the particles of larger aromatic moieties. The results clearly show that photoionization is a powerful diagnostic tool for the physical-chemical characterization of combustion aerosol, and it may lead to further insights into the soot formation mechanism.

[1]  H. Burtscher,et al.  Probing aerosols by photoelectric charging , 1982 .

[2]  P. R. Westmoreland,et al.  Recent contributions of flame-sampling molecular-beam mass spectrometry to a fundamental understanding of combustion chemistry , 2009 .

[3]  A. Schmidt-Ott,et al.  Particle charge in combustion aerosols , 1986 .

[4]  G. Reischl,et al.  Bipolar charging of ultrafine particles in the size range below 10 nm , 1996 .

[5]  R. Niessner,et al.  Laboratory experiments on the determination of polycyclic aromatic hydrocarbon coverage of submicrometer particles by laser-induced aerosol photoemission , 1989 .

[6]  Sotiris E. Pratsinis,et al.  Flame aerosol synthesis of smart nanostructured materials , 2007 .

[7]  L. A. Sgro,et al.  Surface enhanced Raman spectroscopy (SERS) of particles produced in premixed flame across soot threshold , 2011 .

[8]  M. Aldén,et al.  Optical investigation of laser-produced C2 in premixed sooty ethylene flames ☆ , 1990 .

[9]  C. Myung,et al.  Exhaust nanoparticle emissions from internal combustion engines: A review , 2011 .

[10]  F. Beretta,et al.  SOOT AND NANOPARTICLE FORMATION IN LAMINAR AND TURBULENT FLAMES , 2007 .

[11]  G. Steiner,et al.  The effect of carrier gas contaminants on the charging probability of aerosols under bipolar charging conditions , 2012, Journal of aerosol science.

[12]  H. Burtscher,et al.  In situ measurement of adsorption and condensation of a polyaromatic hydrocarbon on ultrafine C particles by means of photoemission , 1986 .

[13]  Müller,et al.  Photoemission from small metal spheres: A model calculation using an enhanced three-step model. , 1988, Physical review. B, Condensed matter.

[14]  H. Burtscher,et al.  Monitoring Particulate Emissions from Combustions by Photoemission , 1988 .

[15]  F. Qi.  Combustion chemistry probed by synchrotron VUV photoionization mass spectrometry , 2013 .

[16]  A. Wiedensohler,et al.  Investigation of the bipolar charge distribution at various gas conditions , 1986 .

[17]  M. Zachariah,et al.  Size resolved particle work function measurement of free nanoparticles: Aggregates vs. spheres , 2012 .

[18]  H. Burtscher.  Measurement and characteristics of combustion aerosols with special consideration of photoelectric charging and charging by flame ions , 1992 .

[19]  P. Minutolo,et al.  The optical band gap model in the interpretation of the UV-visible absorption spectra of rich premixed flames , 1996 .

[20]  A. Maisels,et al.  On the effect of charge recombination on the aerosol charge distribution in photocharging systems , 2003 .

[21]  Andrea D’Anna,et al.  Combustion-formed nanoparticles , 2009 .

[22]  L. A. Sgro,et al.  Charge fraction distribution of nucleation mode particles: New insight on the particle formation mechanism , 2011 .

[23]  Peter Schurtenberger,et al.  Enormous Yield of Photoelectrons from Small Particles , 1980 .

[24]  M. Aigner,et al.  Distinction of gaseous soot precursor molecules and soot precursor particles through photoionization mass spectrometry. , 2007, Rapid communications in mass spectrometry : RCM.

[25]  A. D’Anna,et al.  The spectroscopic characterisation of UV absorbing nanoparticles in fuel rich soot forming flames , 1998 .

[26]  Antonio D'Alessio,et al.  Optical characterization of rich premixed CH4/O2 flamesacross the soot formation threshold , 1994 .

[27]  Henning Bockhorn,et al.  Soot Formation in Combustion , 1994 .

[28]  H. Burtscher,et al.  Multiple charging of ultrafine aerosol particles by aerosol photoemission (APE) , 1988 .

[29]  P. Glarborg,et al.  Particle Emissions from Domestic Gas Cookers , 2010 .

[30]  A. Ciajolo,et al.  Study on the contribution of different molecular weight species to the absorption UV–Visible spectra of flame-formed carbon species , 2013 .

[31]  Juan Wang,et al.  Absolute photoionization cross-sections of some combustion intermediates , 2012 .

[32]  P. Desgroux,et al.  Study of the formation of soot and its precursors in flames using optical diagnostics , 2013 .

[33]  R. Niessner,et al.  Ultrafine particles as trace catchers for polycyclic aromatic hydrocarbons: the photoelectric aerosol sensor as a tool for in situ sorption and desorption studies , 1989 .

[34]  H. Mätzing,et al.  Detection of electrically charged soot particles in laminar premixed flames , 2012 .

[35]  R. Niessner.  The chemical response of the photo-electric aerosol sensor (PAS) to different aerosol systems , 1986 .

[36]  Bin Zhao,et al.  Analysis of Soot Nanoparticles in a Laminar Premixed Ethylene Flame by Scanning Mobility Particle Sizer , 2003 .

[37]  K. Sattler,et al.  Evaluation of an in situ sampling probe for its accuracy in determining particle size distributions from flames , 1997 .

[38]  P. R. Westmoreland,et al.  "Imaging" combustion chemistry via multiplexed synchrotron-photoionization mass spectrometry. , 2008, Physical chemistry chemical physics : PCCP.

[39]  Giuseppe Toniato,et al.  Emission of Ultrafine Particles from Natural Gas Domestic Burners , 2008 .

[40]  J. H. Miller,et al.  Experimental and computational determinations of optical band gaps for PAH and soot in a N2-diluted, ethylene/air non-premixed flame , 2013 .

[41]  A. D’Anna,et al.  Size Measurements of Fluorescent Carbon Nanoparticles in a Coflowing Laminar Diffusion Flame by Time-Resolved Fluorescence Anisotropy , 2012 .

[42]  A. C. Barone,et al.  Measurement of nanoparticles of organic carbon in non-sooting flame conditions , 2009 .

[43]  H. Burtscher,et al.  Experiments on small particles in gas suspension , 1985 .

[44]  Hai Wang.  Formation of nascent soot and other condensed-phase materials in flames , 2011 .

[45]  A. Wiedensohler,et al.  An approximation of the bipolar charge distribution for particles in the submicron size range , 1988 .

[46]  Yuyang Li,et al.  Recent applications of synchrotron VUV photoionization mass spectrometry: insight into combustion chemistry. , 2010, Accounts of chemical research.

[47]  J. Kent,et al.  Nano organic carbon and soot in turbulent non-premixed ethylene flames , 2007 .

[48]  M. Aigner,et al.  Simultaneous detection of two types of soot precursor particles using photoionization mass spectrometry. , 2007, Rapid communications in mass spectrometry : RCM.