Image analysis techniques for transmission electron microscopy analysis of carbonaceous and related particles and their application

Transmission electron microscopy (TEM) provides direct imaging of the nanoscale particles that make up an aerosol. A wealth of information can be gleaned from such images. Here, we examine the use of TEM to characterize carbonaceous and related (e.g., ash) particles. In this context, TEM provides a tangible visualization of particle morphology, easily differentiating fractal and spherical morphologies, and often allows for a rough assessment of mixing state. Historically, quantitative extraction of this information has required manual analysis of the TEM images. While still the most accurate analysis route, such analysis can be prohibitively labour intensive. This has naturally led to the development of automated analysis methods, with several flavors. At the same time, there are also gaps in representing information derived from TEM images. For example, there is some debate about how to represent primary particle size and the degree to which the property is meaningful. This work examines several advances in the field of image analysis for TEM over the past decade, discussing several automated methods and what information can be gleaned from such automated methods. We demonstrate the practical application of TEM to characterize particles from several sources over the past decade, spanning aircraft turbines, marine engines, biomass burning, and atmospheric samples. We conclude by discussing what might be next and how the literature continues to evolve.