10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Characterization of a New MiniCAST Generator (Model 5201 Type BC) Offering Both Diffusion and Premixed Flame Option
MICHAELA N. ESS, Konstantina Vasilatou, METAS
Abstract Number: 117 Working Group: Combustion
Abstract Black carbon (BC), light-absorbing carbonaceous substances in atmospheric aerosol [1], is known to have a huge impact on climate as well as on the human health. It is generated by combustion of natural as well as anthropogenic origin. With the potential of causing diseases, direct influence on the earth’s radiation budget and also indirect effects e.g. as cloud condensation nuclei, BC is one of the atmospheric components strongly monitored. Optical absorption methods, filter based as well as filter free ones, are normally used for the monitoring of BC. Since for common filter-based methods the measurement is affected by the filter type and particle properties, the application of a general calibration factor is impossible. To apply a standardized calibration for specific particle types, standard aerosol sources generating particles with well-defined physical parameters, which can be used to quantify aerosol absorption with traceability to primary standards, are needed. The development and characterization of such sources in one of the goals of the EMPIR 16ENV02 Black Carbon project.
In this context, we are investigating the optical, physical and chemical properties of the carbonaceous aerosols produced by the new miniCAST soot generator Model 5201 Type BC (Jing Ltd.). In contrast to former CAST models, which rely entirely on diffusion flames of a fuel (often diluted with nitrogen) and air, the new model offers the possibility of: i) adding air instead of nitrogen to the fuel (in this case propane gas) to achieve different levels of premixing; ii) adding oxygen to the oxidation air; iii) adding oxygen to the quench gas.
Although a completely premixed flame is not possible because the (premixed) propane is still surrounded by an oxidation air cone causing also diffusion flame conditions, the versatility of the new miniCAST model offers further possibilities to tune the properties of the generated BC particles.
These are analyzed with respect to their size, number and mass concentration using an SMPS and a TEOM, while an Aethalometer is used to determine the BC mass concentration and the Ångstrom absorption exponent α. Additionally, the microstructure and the chemical composition of the particles is characterized with micro-Raman Spectroscopy and OC/EC analysis, respectively.
By operating the new miniCAST with a normal diffusion flame, particles with geometric mean diameter (GMD) up to 180 nm can be achieved with improved stability and reproducibility compared to older models. While at overall fuel rich conditions the EC content decreases fast with decreasing particle size, at fuel lean conditions also smaller particles (GMD ≥ 65 nm) with high EC content (≥ 85 %) and low α (≤ 1.4) can be generated even without volatile particle remover.
Using the premixing option, smaller particles were generated at the same overall fuel-to-air ratio compared to the pure diffusion flame. Thereby it seems to be possible to also generate particles with GMD ≥ 30nm and increased BC fraction compared to older CAST models.
In this work, a detailed characterization of the aerosol properties at different operation points of the CAST generator will be presented.
This work is part of the 16ENV02 Black Carbon project funded by the European Union through the European Metrology Programme for Innovation and Research (EMPIR).
[1] Petzold, A., Ogren, J. A., Fiebig, M., Laj, P., Li, S.-M., Baltensperger, U., Holzer-Popp, T., Kinne, S., Pappalardo, G., Sugimoto, N., Wehrli, C., Wiedensohler, A., and Zhang, X.-Y. (2013), Atmos. Chem. Phys.13, 8365-8379.