## 3 Results and Discussion
### Elemental Analysis  
#### 3.3.1 High-Altitude Samples  
Through the EDX maps, it is observed that many of the particulates appear to be well mixed chemically and contain regions with somewhat even distributions of different  
Figure 5: Assorted SEM images of high altitude sampled particulates (**a**) compound spherical particulate with various surface deposits; (**a2**) hollow spherical surface deposit of frame A corresponding with black arrow; (**a3**) spherical deposits on the surface of frame A corresponding with the white arrow; (**b**) single semi-spherical particulate; (**b2**) high-resolution image of frame B showing hollow semi-spherical composition corresponding with white arrow; (**c**) double spherical particulate; (**c2**) crystalline surface deposits on frame C corresponding with white arrow; (**c3**) amorphous surface deposits on frame C corresponding with dashed white arrow; (**d**) particulate cluster; (**e**) single compound particulate; (**e2**) image focused on spherical deposits of frame E corresponding with white arrow; (**f**) single semi-spherical particulate. elements. This is true for the particle seen in Figure 6(a1) and the corresponding maps of oxygen, magnesium, barium, and aluminum of the particle. Figure 6: Energy dispersive X-ray (EDX) maps and EDX spectra collected on selected airborne particulate matter of high-altitude fireworks. **(a1)** Secondary electron SEM image of a porous-like particulate morphology; **(a2-a5)** EDX maps of O-K, Mg-K, Ba-L, and Al-K on the porous structure; **(a6)** associated EDX spectra; **(b1)** secondary electron SEM image of a spheroidal-like structure; **(b2-b5)** EDX maps of Mg-K, Ba-L, Al-K, and O-K; **(b6)** associated EDX spectra; **(c1)** secondary electron SEM image of large spheroidal with a smaller particle diffused to its surface; **(c2-c6)** EDX maps of elements present including Sr-K, O-K, Mg-K, Fe-K, Cu-K; **(c7)** overlaid EDX map showing the distinct elemental regions within the particle; **(c8)** is the spectra of the large spheroidal and diffused particle. The same trend is seen in the particle imaged in Figure 6(b1), as its corresponding maps between Figure 6(b2-b5) show a nearly uniform distribution of the mapped elements within the nearly perfectly spherical particle. This observed uniform distribution is much more interesting, however, for the particle imaged in Figure 6(c1). In the corresponding maps of this particle, it is observed that there are regions of uniformity that contain certain specific elements while other regions feature other elements almost exclusively. Figure 6(c7) features an overlay of different maps with the observed regions outlined. These observed patterns in chemical composition, alongside the proposed formation mechanism of multistage particulate formation, could indicate that the particulate conglomeration process is not necessarily uniform within a given region. As seen in the EDX analysis, various alkaline and transition metals including Al, Ba, Sr, Cu, and Fe were detected within the samples using both point analysis and elemental mapping as seen above in Figure 6(a2-a5,b2-b5,c2-c7). The presence of these elements is expected, as previously noted due to the role these elements serve in creating certain colors and effects within fireworks. It should be noted that many of the spectra produced during EDX analysis indicated the presence of iridium. This is a result of using iridium sputter-coating to reduce the effect of charging in the sample and enhance the quality of the imaging. Figure 6(a2-a5) indicate that the imaged particulate is a compound particulate with the signature of oxygen, magnesium, barium, and aluminum which suggests that these elements potentially came from a common origin and were mixed in a gaseous state prior to forming a particulate.