## 3 Results and Discussion
### Local Particle Characteristics Probed by TS-TEM
#### 3.2.2 TS-TEM Conducted at 5 cm HAB  
At 5 cm HAB, by applying sufficient low thermophoretic sampling times, particles can be selectively extracted either from different flame activities. Here, samples were taken by trial-and-error experiments using a sampling time of \(t_{\text{s}}\) = 1.5 ms. In these experiments, extraction procedures were monitored using high-speed imaging (Fastcam SA-X2 1080K-M3 camera, Photron Deutschland GmbH, Reutlingen, Germany), and afterward, it was evaluated to which activity the extracted sample was related to. The corresponding high-speed data is available online (www.spraysyn.org, accessed on 1 February 2025). By conducting trial-and-error experiments this way, we obtained samples predominately corresponding to either flame flickering or flame pulses, and representative particle structures present 5 cm _HAB_ are illustrated in Figure 10. There, Figure 10a represents particle structures present in flame flickering, while Figure 10b depicts particle structures present in flame pulses. As shown in Figure 10a, well-crystalline aggregates, aggregates, and non-agglomerated single particles can be readily found within flame flickering. From a subjective point of view, aggregates and agglomerates are most prominent (frames 2, 3, 7), followed by non-aggregated single particles (frames 4, 5). By applying higher magnification, the particles' crystallinity can be evidenced since line patterns can be unambiguously recognized (frames 6, 8). By examining arbitrary particles this way, no evidences of amorphous matter, indicating carbon depositions can be recognized. Figure 9: Structure characteristics of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) particles present at 15 cm HAB using SpraySyn1 while processing 0.1 M INN in EtOH + EHA. Panel (**a**) represents exemplary illustrations obtained by TS-TEM experiments, while (**b**) represents HIAT-SMPS data with \(d_{\text{P,EM}}\) as the particles’ electrical mobility equivalent diameter, \(N\) as number concentration, and \(\sigma_{\text{G,N}}\) as number-weighted distribution width. As shown in Figure 10b, particles present in flame pulses have quite different morphologies. Most importantly, most extracted particles display core-shell structures (frames 3-6). Since these particles exhibit a crystalline core with an amorphous shell, it is indicated that carbon co-exists aside \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) particles. Some layers showed C-onion structures upon magnification, which are typical for ordered carbon (frame 6) [21]. Aside from core-shell structures, also entirely amorphous aggregates can be recognized, indicating soot [58],  
Figure 10: Structure characteristics of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) particles present at 5 cm HAB using SpraySyn1 while processing 0.1 M INN in EtOH + EHA. Panel (**a**) illustrates structures present in flame flickering (period of low flame activity), while (**b**) depicts particle morphologies present in pulses (period of high flame activity). and a corresponding structure is depicted in frame 7. Even at higher magnification, corresponding particles do not display any line pattern, unambiguously evidencing an absence of crystallinity (frame 8). All these structures co-exist aside crystalline \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) particles (frame 2). In relation, TS-TEM experiments conducted at 5 cm indicate that elementary carbon forms as side products aside from \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) within flame pulses at 5 cm \(HAB\) when processing 0.1 M INN in EtOH + EHA using SpraySyn1. Since particles extracted from the flickering are crystalline, it is suggested that fuel-rich conditions are only temporarily present in flame pulses, causing a temporal/local oxygen deficiency promoting the formation of carbon there. Since no evidence is given for carbon by conducting TS-TEM experiments at 15 cm \(HAB\), it is further suggested that carbon depositions oxidize/decompose further downstream.