scholarly journals Structural changes of CAST soot during a thermal-optical measurement protocol

2019 ◽  
Author(s):  
Theresa Haller ◽  
Christian Rentenberger ◽  
Jannik C. Meyer ◽  
Laura Felgitsch ◽  
Hinrich Grothe ◽  
...  
Keyword(s):  
Structural Changes ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Domain Size ◽  
Carbonaceous Material ◽  
Total Carbon ◽  
Integrating Sphere ◽  
Heating Process ◽  
Continuous Change ◽  
Measurement Protocol

Abstract. Thermal-optical measurement techniques are widely used to classify carbonaceous material. The results of different methods for total carbon are comparable, but can vary by > 44 % for elemental carbon. One major cause of variation is the formation of pyrolyzed carbon during the heating process which occurs mainly in samples with a high amount of brown carbon (BrC). In this study the structural changes of two different CAST aerosol samples caused by the heating procedure in a thermal-optical instrument were investigated with UV-VIS and Raman spectroscopy, the Integrating Sphere technique and transmission electron microscopy. All analysis techniques showed significant structural changes for BrC rich samples at the highest temperature level (870 °C) in helium. The structure of the heated BrC-rich sample resembles the structure of an unheated BrC-poor sample. Heating the BrC rich sample to 870 °C increases the graphitic domain size within the material from 1.6 nm to 2 nm. Although the Raman spectra unambiguously show this increase of ordering only at the highest temperature step, UV-VIS and IS analyses show a continuous change of the optical properties also at lower temperatures. The sample with a negligible amount of BrC, however, did not show any significant structural changes during the whole heating procedure.

scholarly journals Structural changes of CAST soot during a thermal–optical measurement protocol

2019 ◽  
Vol 12 (7) ◽  
pp. 3503-3519 ◽  
Author(s):  
Theresa Haller ◽  
Christian Rentenberger ◽  
Jannik C. Meyer ◽  
Laura Felgitsch ◽  
Hinrich Grothe ◽  
...  
Keyword(s):  
Structural Changes ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Domain Size ◽  
Carbonaceous Material ◽  
Total Carbon ◽  
Integrating Sphere ◽  
Heating Process ◽  
Continuous Change ◽  
Measurement Protocol

Abstract. Thermal–optical measurement techniques are widely used to classify carbonaceous material. The results of different methods for total carbon are comparable but can vary by >44 % for elemental carbon. One major cause of variation is the formation of pyrolyzed carbon during the heating process which occurs mainly in samples with a high amount of brown carbon (BrC). In this study the structural changes of two different CAST (combustion aerosol standard) aerosol samples caused by the heating procedure in a thermal–optical instrument were investigated with UV–VIS and Raman spectroscopy, the integrating-sphere technique (IS) and transmission electron microscopy. All analysis techniques showed significant structural changes for BrC-rich samples at the highest temperature level (870 ∘C) in helium. The structure of the heated BrC-rich sample resembles the structure of an unheated BrC-poor sample. Heating the BrC-rich sample to 870 ∘C increases the graphitic domain size within the material from 1.6 to 2 nm. Although the Raman spectra unambiguously show this increase in ordering only at the highest temperature step, UV–VIS and IS analyses show a continuous change in the optical properties also at lower temperatures. The sample with a negligible amount of BrC, however, did not show any significant structural changes during the whole heating procedure.

Investigation of structural changes of 21 atmospheric aerosol samples during a thermal-optical measurement procedure (EUSAAR2)

2020 ◽  
Author(s):  
Theresa Haller ◽  
Eva Sommer ◽  
Thomas Steinkogler ◽  
Anna Wonaschuetz ◽  
Anne Kasper-Giebl ◽  
...  
Keyword(s):  
Atmospheric Aerosol ◽  
Structural Changes ◽  
Optical Measurement ◽  
Ionic Composition ◽  
Measurement Techniques ◽  
Water Soluble ◽  
Integrating Sphere ◽  
Brown Carbon ◽  
High Tendency ◽  
Air Mass

<p>Elemental Carbon (EC), Black Carbon (BC) and Organic Carbon (OC) contribute a large amount to atmospheric aerosols. Due to their significant influence on climate and health, a reliable measurement of these components is essential. Nevertheless, their correct determination is not trivial and results of different measurement techniques show differences by factors up to nine especially in the presence of Brown Carbon (BrC) (e.g. Reisinger et al., 2008; Hitzenberger et al., 2006; Wonaschuetz et al., 2009). EC and OC are usually measured with thermal-optical techniques: The sample is heated stepwise, first in an inert (He) atmosphere, then in an oxidizing (He+O<sub>2</sub>) atmosphere. The darkening of the sample during the heating procedure is traced with a laser transmission/reflection signal. Based on the progress of this signal, the amount of pyrolyzed carbon is calculated and attributed to OC in the subsequent evaluation. Despite this optical correction, the pyrolyzation of OC can lead to uncertainties in the OC/EC split (Cheng et al., 2012). Especially Brown Carbon (BrC) and water soluble organic carbons (WSOC) have a high tendency to pyrolyze and therefore bias the OC/EC split. Moreover several metal salts in the atmospheric aerosol can influence the measurement process and enhance or suppress pyrolysis of OC (Wang et al., 2010). These highly complex chemical and physical reactions are not fully investigated yet but are essential for a profound understanding of the biases in thermal-optical measurement techniques. </p><p>The aim of the present study was to investigate the structural reorganizations of the carbonaceous materials in atmospheric aerosol samples occurring during a thermal-optical heating procedure (EUSAAR2, Cavalli et al., 2010) and to set them in relation with several properties of the samples such as ionic composition, EC, OC, BC and BrC, as well as the air mass origins during sampling of the atmospheric aerosol samples. <br>The changes of the internal structure of the material during the heating procedure of an EC/OC analyzer (Sunset instruments) were analyzed with Raman spectroscopy, which is sensitive to C-C bonding types and to the degree of structural ordering within the sample (Ferrari and Robertson, 2000). Different types of restructuration behavior were defined depending on the temperature levels of the EUSAAR2 protocol where measurable structural changes occur. For all samples ion chromatography was performed with a Dionex Aquion system (Thermo Fisher), BrC and BC were analyzed with the Integrating Sphere method (Wonaschütz et al., 2009) and air mass back trajectories for the respective sampling days were calculated with HYSPLIT.</p>

scholarly journals Investigation of structural changes of atmospheric aerosol samples during two thermal-optical measurement procedures (EUSAAR2, NIOSH870)

2020 ◽  
Author(s):  
Theresa Haller ◽  
Eva Sommer ◽  
Thomas Steinkogler ◽  
Christian Rentenberger ◽  
Anna Wonaschuetz ◽  
...  
Keyword(s):  
Raman Spectra ◽  
Atmospheric Aerosol ◽  
Structural Changes ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Water Soluble ◽  
Total Carbon ◽  
Brown Carbon ◽  
Structural Ordering ◽  
Temperature Levels

Abstract. Thermal-optical measurement techniques are widely used for the monitoring of carbonaceous aerosols. Although results of different thermal-optical measurement techniques are comparable for total carbon, they can vary widely for values of elemental carbon especially in the presence of brown carbon. Charring of organic material during the inert heating phase of thermal-optical measurements was found to be a major confounder, but no literature about investigations of structural changes during this process in atmospheric aerosols is available. In a recent study we investigated these structural changes for combustion aerosol standard soot (CAST). Now we apply this approach to selected atmospheric aerosol filter samples and a subset of eight washed filter samples with low WSOCs loadings. To investigate structural changes, Raman spectra were obtained for samples heated to the corresponding temperature levels and gas atmospheres of the EUSAAR2 and NIOSH870 protocols. The temperature levels where changes in the Raman spectra occurred (i.e. changes in structure) varied for different samples. For the washed samples with low WSOC loadings and absence of other water soluble aerosol components such as inorganic salts, changes in structural ordering and darkening of the samples were not observed. For all samples, ion chromatography, integrating sphere measurements (yielding black and brown carbon data) and thermal-optical analyses were performed. We were able to show for the first time that the darkening of a sample (measured in terms of transmission laser signal) is not necessarily caused by an increase of structural ordering in the sample. Therefore we suggest that the widely used term charring should be used carefully when the darkening of a sample during thermal-optical measurement procedures is interpreted.

scholarly journals Investigation of structural changes of atmospheric aerosol samples during two thermal–optical measurement procedures (EUSAAR2, NIOSH870)

2021 ◽  
Vol 14 (5) ◽  
pp. 3721-3735
Author(s):  
Theresa Haller ◽  
Eva Sommer ◽  
Thomas Steinkogler ◽  
Christian Rentenberger ◽  
Anna Wonaschuetz ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Raman Spectra ◽  
Atmospheric Aerosol ◽  
Structural Changes ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Water Soluble ◽  
Total Carbon ◽  
Structural Ordering ◽  
Temperature Levels

Abstract. Thermal–optical measurement techniques are widely used for the monitoring of carbonaceous aerosols. Although results of different thermal–optical measurement techniques are comparable for total carbon, they can vary widely for values of elemental carbon especially in the presence of brown carbon. Charring of organic material during the inert heating phase of thermal–optical measurements has been found to be a major confounder, but no literature about investigations of structural changes during this process in atmospheric aerosols is available. In a recent study we investigated these structural changes for combustion aerosol standard (CAST) soot. Now we apply this approach to selected atmospheric aerosol filter samples and a subset of eight washed filter samples with low loadings of water-soluble organic carbon (WSOC). To investigate structural changes, Raman spectra were obtained for samples heated to the corresponding temperature levels and gas atmospheres of the EUSAAR2 and NIOSH870 protocols. The temperature levels where changes in the Raman spectra occurred (i.e., changes in structure) varied for different samples. For the washed samples with low WSOC loadings and absence of other water-soluble aerosol components such as inorganic salts, changes in structural ordering and darkening of the samples were not observed. We were able to show for the first time that the darkening of a sample (measured in terms of transmission laser signal) is not necessarily caused by an increase of structural ordering in the sample. Possible transformations at lower temperatures could include a formation of non-graphitic light-absorbing intermediate organic carbon, a release of C−H groups or a decrease of carbonyl groups.

scholarly journals Assessing recent measurement techniques for quantifying black carbon concentration in snow

2012 ◽  
Vol 5 (3) ◽  
pp. 3771-3795 ◽  
Author(s):  
J. P. Schwarz ◽  
S. J. Doherty ◽  
F. Li ◽  
S. T. Ruggiero ◽  
C. E. Tanner ◽  
...  
Keyword(s):  
Black Carbon ◽  
Single Particle ◽  
Carbon Concentration ◽  
Mass Concentration ◽  
Measurement Techniques ◽  
Integrating Sphere ◽  
Recent Measurement ◽  
Atmospheric Sampling ◽  
Careful Assessment ◽  
Snow Samples

Abstract. We evaluate the performance of the Single Particle Soot Photometer (SP2) and the Integrating Sphere/Integrating Sandwich Spectrophotometer (ISSW) in quantifying the concentration of refractory black carbon (BC) in snow samples. We find that the SP2 can be used to measure BC mass concentration in snow with substantially larger uncertainty (60%) than for atmospheric sampling (<30%). Achieving this level of accuracy requires careful assessment of nebulizer performance and SP2 calibration with consideration of the fact that BC in snow tends to larger sizes than typically observed in the atmosphere. Once these issues are addressed, the SP2 is able to measure the size distribution and mass concentration of BC in the snow. Laboratory comparison of the SP2 and the Integrating Sphere/Integrating Sandwich Spectrophotometer (ISSW) revealed significant biases in the estimate of BC concentration from the ISSW when test samples contained dust or non-absorbing particulates. These results suggest that current estimates of BC mass concentration in snow and ice using either the SP2 or the ISSW may be associated with significant underestimates of uncertainty.

scholarly journals Different characteristics of char and soot in the atmosphere and their ratio as an indicator for source identification in Xi'an, China

2010 ◽  
Vol 10 (2) ◽  
pp. 595-607 ◽  
Author(s):  
Y. M. Han ◽  
J.J. Cao ◽  
S. C. Lee ◽  
K. F. Ho ◽  
Z. S. An
Keyword(s):  
Seasonal Variations ◽  
Source Identification ◽  
Carbonaceous Material ◽  
Total Carbon ◽  
Carbonaceous Aerosol ◽  
Poor Correlation ◽  
Minimum Concentration ◽  
Carbonaceous Particles ◽  
Carbon Fractions ◽  
Different Characteristics

Abstract. Numerous definitions and analytical techniques for elemental (or black) carbon (EC) have been published in the scientific literature, but still no generally accepted interdisciplinary definition exists. EC is not a single chemical compound, but is mainly composed of two parts of carbon contents: combustion residues from pyrolysis and combustion emissions formed via gas-to-particle conversion. Accordingly EC is subdivided into two classes: char and soot. Char is defined as carbonaceous materials obtained by heating organic substances and formed directly from pyrolysis, or as an impure form of graphitic carbon obtained as a residue when carbonaceous material is partially burned or heated with limited access of air. Soot is defined as only those carbon particles that form at high temperature via gas-phase processes. Since the different classes of EC have different chemical and physical properties, their optical light-absorbing properties differ, so that it is essential to differentiate them in the environment. The thermal optical reflectance (TOR) method was used to differentiate between char-EC and soot-EC according to its stepwise thermal evolutional oxidation of different carbon fractions under different temperatures and atmosphere. Char-EC and soot-EC are operationally defined as EC1-OP and EC2+EC3 (EC1, EC2 and EC3 corresponding to carbon fractions evolved at 550, 700 and 800 °C in a 98% He/2% O2 atmosphere, respectively), respectively. One year of observations of the daily and seasonal variations of carbonaceous particles were conducted in Xi'an, China in 2004 to demonstrate the different characteristics of char and soot in the atmosphere. Total carbon (TC), organic carbon (OC), EC and char-EC showed similar seasonal trends, with high concentrations in winter and low concentrations in summer, while soot-EC revealed relatively small seasonal variations, with maximum concentration (1.85±0.72 μg m−3) in spring and minimum concentration (1.15±0.47 μg m−3) in summer. The strong correlation between EC and char-EC (R2 = 0.99) and poor correlation between EC and soot-EC (R2 = 0.31) indicate that previously reported total EC in the literature reflected the distribution characteristics of char only, while overlooking that of soot. However, soot exhibits stronger light-absorbing characteristics than char, and merits greater focus in climate research. The small seasonal variation of soot-EC indicates that soot may be the background fraction in total EC, and is likely to have an even longer lifetime in the atmosphere than previously estimated for total EC, which suggests that soot may has a greater contribution to global warming. While both char-EC/soot-EC and primary OC/EC ratios vary with emission sources, only OC/EC ratio is affected by SOA. Thus char-EC/soot-EC may be a more effective indicator than OC/EC in source identification of carbonaceous aerosol. Comparison of seasonal variations of OC/EC and char-EC/soot-EC ratios in Xi'an confirms this point. However, wet scavenging by snow and rain was more effective for char than for soot and influenced the char-EC/soot-EC ratio, and this factor should be considered in source identification as well.

High Intensity Focused Ultrasound (HIFU) Transducer Characterization Using Acoustic Streaming

2007 ◽  
Author(s):  
Prasanna Hariharan ◽  
Ronald A. Robinson ◽  
Matthew R. Myers ◽  
Rupak K. Banerjee
Keyword(s):  
High Intensity ◽  
Focused Ultrasound ◽  
Optical Measurement ◽  
Measurement Techniques ◽  
Acoustic Streaming ◽  
Acoustic Power ◽  
High Intensity Focused Ultrasound ◽  
Medical Ultrasound ◽  
Intensity Field ◽  
Streaming Velocity

A new, non-perturbing optical measurement technique was developed to characterize medical ultrasound fields generated by High Intensity Focused Ultrasound (HIFU) transducers using a phenomenon called ‘acoustic streaming’. The acoustic streaming velocity generated by HIFU transducers was measured experimentally using Digital Particle Image Velocimetry (DPIV). The streaming velocity was then calculated numerically using the finite-element method. An optimization algorithm was developed to back-calculate acoustic power and intensity field by minimizing the difference between experimental and numerical streaming velocities. The intensity field and acoustic power calculated using this approach was validated with standard measurement techniques. Results showed that the inverse method was able to predict acoustic power and intensity fields within 10% of the actual value measured using standard techniques, at the low powers where standard methods can be safely applied. This technique is also potentially useful for evaluating medical ultrasound transducers at the higher power levels used in clinical practice.

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