## 3 Results and Discussion
### Particulate Sizing  
#### 3.2.1 Low-Altitude Samples  
Figure 4 shows SEM images of the airborne \"as-trapped\" particulates collected on disks at the low altitude sampling. It appears that the smoke plume resulted from personal fireworks (or samples from LAS) is composed of a variety of particulates (e.g., shape and size). Samples taken at the low altitude often featured particles with a \"rocky\" type construction as seen in Figure 4a,b,e. Figure 4a shows a large irregularly shaped structure with multiple sharp edges and a coarse surface texture. A higher resolution SEM image of the boxed area in Figure 4a shows that smaller shapeless particles are deposited on the surface of this larger structure (Figure 4(a2)). Figure 4b shows a relatively large cohesive particle with multiple facets and a smooth surface surrounded by smaller shapeless particles. This can be seen best in Figure 4c,d, especially within Figure 4c as many of the particulates imaged appear to be on the smaller end of the micro-scale and well below the threshold for PM\({}_{2.5}\). The LAS group also had a larger number of sampled particulates, which has two potential causes. Figure 4: Assorted SEM images of low-altitude sampled particulates; (**a**) single particulate with surface deposition; (**a2**) high-resolution image of particulate A deposited material corresponding with the white arrow of particle A; (**b**) particulate cluster; (**c**) large particulate cluster with many particles on a nano-scale; (**d**) particulate cluster; (**d2**) high-resolution image of particulate D with emphasis on splatter-formation of particulate matter corresponding with the white arrow of particulate D; (**e**) single particulate; (**f**) extended particulate cluster; (**f2**) high-resolution image of frame F showing smaller length scale corresponding with the white arrow of F; (**g**) spherical composite particulate; (**g2**) high resolution of smaller spherical particulates attached to frame G corresponding with the white arrow of particulate G; (**g3**) high resolution of non-spherical deposits on frame G corresponding with the black arrow. The LAS samples were taken at a lower altitude closer to the source, meaning it was significantly easier to ensure that the drone platform remained fully within the plumes originating from the various fireworks sources. This trend was also supported by how LAS samples were taken earlier in the evening, as the smaller personal fireworks used by the general public were greater in number and much closer than their professional counterparts. The samples taken at this lower altitude also displayed a more diverse array of physical compositions as seen in Figure 4 with a diverse array of both sizes and shapes within the particulates collected. Many of these imaging results are similar in size and shape to particulate residue found in gunshot residue by [PERSON] et al. in 2019 [31]. Their work was focused on differences between swabs of non-shooters and shooters in order to detect certain chemicals in the residue [31]. In their included SEM imaging of detected particulates in gunshot residue, many similar structures are seen which is reasonable considering that in both cases the propellant is the same compound--gunpowder [31]. In the LAS samples, it is observed that the morphology of the finer structures differs greatly between the samples collected. Figure 4a,g display larger particulates with smaller deposits of material, as indicated by the arrows in each Frame with higher resolution images focused on surface deposits seen in Figure 4(a2,g2,g3). Figure 4c,d display clusters composed of very fine particulate distribution, in a \"splatter\" formation where the particulates appear randomly distributed in a given area with little organization, including particulates that appear stacked on one another as seen in Figure 4c. Many of the particulates in Figure 4c,d appear to be of the same construction with many being hexagonal in shape, indicating that this could be a common particulate type being formed during the firework displays.