title: Online determination of polycyclic aromatic hydrocarbon formation from a flame soot generator.
abstract: In this study, we produced a class of diffusion flame soot particles with varying chemical and physical properties by using the mini-Combustion Aerosol STandard (CAST) and applying varying oxidant gas flow rates under constant propane, quenching, and dilution gas supply. We varied the soot properties by using the following fuel-to-air equivalence ratios (Φ): 1.13, 1.09, 1.04, 1.00, 0.96, and 0.89. Within this Φ range, we observed drastic changes in the physical and chemical properties of the soot. Oxidant-rich flames (Φ < 1) were characterized by larger particle size, lower particle number concentration, higher black carbon (BC) concentration, lower brown carbon BrC.[BC](-1) than fuel-rich flames (Φ > 1). To investigate the polycyclic aromatic hydrocarbons (PAH) formation online, we developed a new method for quantification by using the one (13)C-containing doubly charged PAH ion in a high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS). The time-resolved concentration showed that the larger PAHs prevailed in the fuel-rich flames and diminished in the oxidant-rich flames. By comparison with the offline in situ derivatization-thermal-desorption gas-chromatography time-of-flight mass spectrometry (IDTD-GC-ToF-MS), we found that the concentration by using the HR-ToF-AMS was underestimated, especially for lower mass PAHs (C14-C18) in the fuel-rich flames possibly due to size limitation and degradation of semi-volatile species under high vacuum and desorption temperature in the latter. For oxidant-rich flames, the large PAHs (C20 and C22) were detected in the HR-ToF-AMS while it was not possible in IDTD-GC-ToF-MS due to matrix effect. The PAH formation was discussed based on the combination of our results and with respect to Φ settings.
authors.affiliation: Joint Mass Spectrometry Center, Cooperation Group Comprehensive Molecular Analytics, Helmholtz Zentrum Muenchen, Ingolstaedter Landstr. 1, 85764, Neuherberg, Germany.
authors.forename: Laarnie
authors.initials: L
authors.lastname: Mueller
authors.forename: Gert
authors.initials: G
authors.lastname: Jakobi
authors.forename: Juergen
authors.initials: J
authors.lastname: Orasche
authors.forename: Erwin
authors.initials: E
authors.lastname: Karg
authors.forename: Martin
authors.initials: M
authors.lastname: Sklorz
authors.forename: Gülcin
authors.initials: G
authors.lastname: Abbaszade
authors.forename: Benedict
authors.initials: B
authors.lastname: Weggler
authors.forename: Lianpeng
authors.initials: L
authors.lastname: Jing
authors.forename: Juergen
authors.initials: J
authors.lastname: Schnelle-Kreis
authors.forename: Ralf
authors.initials: R
authors.lastname: Zimmermann
mesh_terms: D000336:Aerosols / Q000032:analysis; D000393:Air Pollutants / Q000032:analysis*; D004867:Equipment Design; D017745:Incineration / Q000295:instrumentation*; D013058:Mass Spectrometry; D010316:Particle Size; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis*; D053260:Soot / Q000032:analysis*
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D011084:Polycyclic Aromatic Hydrocarbons; D053260:Soot