SPOTLIGHT: Structure of carbonaceous aggregate size may be affected by the method of combustion.

February 2019, written by Adrian Li & Dr. Alberto Baldelli

BIF equipment used : Hitachi H7600, FEI Tecnai G2, ThermoFisher Inspect 3D, AMIRA

Carbonaceous aggregates are produced from a combustion process. Their nano-range dimension and their chemical structure make these carbonaceous aggregate harmful to the human health and the environment. Prior studies suggest that nano-sized particles can travel further into the respiratory system and embed into lung tissue making it harder for the body to expel. Additionally, nanoparticles are also good surfaces for toxins and heavy metals to adsorb to further increasing the particle’s toxicity. Larger-sized particles become trapped in the mucous of the upper respiratory system and are relatively easier to remove from the body. Besides, soot nanoparticles are composed of carbon-based molecules called polycyclic aromatic hydrocarbons; these are well known to be dangerous for the human health.

A study by Dr. Alberto Baldelli et al. (2019) aimed to identify and characterize soot nanoparticles collected from flare operations using electron microscopy techniques. The overall goal of this study was to determine if different types of combustion is correlated with the emission of a particular sized soot particle. A secondary aim was to validate the 2D image processing method, commonly used to determine the morphological properties of soot nanoparticles.

Using conventional transmission electron microscopy (TEM), 2D images were collected to determine the size and number of particles present. To further verify whether or not the orientation of particles affected the size measurement from 2D images, electron tomography (ET) was used to create 3D constructs of the particle with Thermofisher Inspect 3D and AMIRA software. ET analysis was also able to reveal ring structures in the carbonaceous aggregates, previously unseen in 2D images. As ring structures are correlated with stronger bonds and possible particle rotation during aggregation, this can generate information on the particle formation process.

While the results of the study were helpful, several challenges needed to be resolved prior to being able to collect TEM images. In order to measure the size of individual aggregates, it required for aggregates to be placed on the grid with proper spacing and density. A single random carbonaceous aggregate was chosen from each of five pre-determined areas on the grid. As particle size can vary, a consistent and efficient magnification level was set for collecting images of aggregates. The magnification was set high enough to visualize the details of the aggregate while still being completely visible when samples were rotated to collect electron tomograms.

Overall, TEM and ET offered many benefits to the study by producing high resolution images of soot aggregates and by collecting quantitative data. For more information about TEM or ET techniques, please browse through our website to learn about their different functions and capabilities.

Baldelli, A., Trivanovic, U., and Rogak, SN. (2019) Electron tomography of soot for validation of 2-D image processing and observation of new structural features. Aerosol Science and Technology, 1-8.