Intern gemischte Multikomponenten-Verbrennungsaerosole: Thermochemie und Struktur/Reaktivität-Charakterisierung
Zusammenfassung der Projektergebnisse
Within the framework of the project, the characterization of multicomponent internally mixed combustion aerosol was performed on defined model soot containing Fe oxides or metal salts as well as real particulate ship exhaust samples obtained from two individual sampling campaigns (QUANTIFY and TRANSPHORM). The defined model soot was prepared in house and was used to specifically investigate the influence of one defined inorganic contamination, i.e. Fe oxide, on the soot characteristics in terms of composition, soot structure, and oxidation reactivity. SEM/EDX combined with CA classified iron-containing soot particles into four different groups according to their elemental composition in dependence of Fe content: “Typical soot”, “Elemental carbon”, “Oxidized soot”, and “Soot with iron oxide”. Fe is dominantly present as amorphous Fe (III) oxide that crystallizes upon thermal treatment of soot. Moreover, Fe carbides may be present in minor amounts. The soot structure is barely affected by the metal additive, but the total amount of hydrocarbons as well as the amount of aromatic hydrocarbons and carboxylic acids relative to aliphatic compounds decrease as the metal content is increased as indicated by RM and FTIR experiments. PAS experiments revealed that the addition of iron to the flame drastically increases the Angstrom coefficient of the produced combustion aerosol. TPO and TPD are shown to be useful methods to study the thermo-chemical properties of iron-containing laboratory-produced soot. Typical TPO profiles show a main peak for the combustion of iron-containing soot agglomerates and often an additional shoulder that can be most probably assigned to the combustion of nonvolatile hydrocarbons and/or iron carbides. The temperature of maximum emission Tmax is strongly dependent on the Fe content, as it decreases exponentially with increasing Fe content. Thus, especially at low Fe contents, soot reactivity increases significantly with increasing Fe content. For contents above ~30 % (m/m) Fe, soot reactivity cannot be enhanced by further addition of Fe. Further experiments demonstrated that not only Fe oxides enhance soot oxidation reactivity without impacting the soot structure, but also diverse inorganic salts (NaCl, Na2SO4 CaSO4, and Ce(SO4)2) show the same effect at similar extent. These findings raise severe questions on the feasibility of commonly used thermo-optical techniques for the quantification of organic carbon (OC) and elemental carbon (EC) in soot if contaminated with inorganic compounds. Especially a shift of EC emission into the range, where OC emission is usually assumed, can be expected due to the catalytic activity of inorganic compounds on soot oxidation. This would lead to a significant decrease in EC/OC ratios measured by thermo-optical techniques. As original aerosol samples can contain multiple inorganic contaminations of various characteristics, it is essential to study the effect of individual impurities such as Fe and inorganic salts as presented in this study. In the second part of the project, real particulate ship exhaust samples were obtained from the campaigns QUANTIFY and TRANSPHORM in cooperation with O. Popovicheva and J. Moldanová. ICP-MS, SEM/EDX with combined CA, RM, IC, AAS, and TPO were applied for their detailed study. All samples show high contamination by inorganic material compared to automotive diesel soot samples. Especially Fe oxides, CaSO4 and CaCO3 were frequently identified by RM and FTIR. The composition of individual particles is varying in a wide concentration range of the major elements (C, O) and impurities (Si, S, Ca, V, Fe, and Ni) representative for the fossil origin of heavy fuels. Depending on combustion conditions, fuel, and type of engine, PM is separated into groups of similar morphological and chemical composition. The presence of char, sulfate, and transition element containing groups are specifically related to the combustion of heavy fuel oil, while soot, calcium, silicates, and iron-containing types of particles may be found in any ship emission. The found metal (Fe, V, Ca) contaminations may act as catalysts for particle oxidation in the exhaust aftertreatment system as shown by our TPO experiments. TPO profiles revealed a high degree of diversity concerning the number of emission maxima and Tmax. This is in accordance with the results of our laboratory-produced model soot types internally mixed with Fe or metal salt.
Projektbezogene Publikationen (Auswahl)
- Structure and Reactivity of Laboratory-Produced Soot Containing Iron, European Aerosol Conference EAC 2011, September 4-9th, 2011, Manchester, UK [Best Poster Prize]
H. Bladt, J. Schmid, E. Kireeva, O. Popovicheva, R. Niessner and N. P. Ivleva
- Impact of Fe Content in Laboratory-Produced Soot Aerosol on its Composition, Structure, and Thermo-Chemical Properties. Aerosol Science and Technology, 2012, 46, 1337-1348
H. Bladt, J. Schmid, E. D. Kireeva, O. B. Popovicheva, N. M. Perseantseva, M. A. Timofeev, K. Heister, J. Uihlein, N. P. Ivleva, and R. Niessner
(Siehe online unter https://doi.org/10.1080/02786826.2012.711917) - Thermo-chemical properties of fleet ship emitted aerosols: Relation to composition and structure, European Aerosol Conference EAC 2012, September 2nd-7th, 2011, Granada, Spain [Best Poster Prize]
H. Bladt, J. Schmid, E. D. Kireeva, O. B. Popovicheva, , J. Moldanová, N. P. Ivleva and R. Niessner
