In this work, high-resolution transmission electron microscopy images of microscopic soot emissions from wildfire and from a wide range of anthropogenic combustion sources (e.g., electrical utility and institutional oil boilers, jet aircraft, and heavy-duty diesel trucks) are presented. The soot nanostructures of individual particles in these emissions are predominantly heterogeneous, decidedly influenced by the fuel composition and by the particular combustion process the fuels undergo, and reveal the mechanisms underlying primary soot particle inception and growth. A lattice fringe analysis shows that differences among the soot nanostructures are measurable. To study whether these differences might identify the combustion source types contributing to ambient aerosols, we also examine the nanostructures of individual atmospheric particles collected at two spatially diverse United States locations (Duke Forest, North Carolina, and the Northern Front Range, Colorado). We find that the elemental carbon structure in airborne particles is mixed internally and externally and does, in fact, reflect contributions from different anthropogenic and biomass burning sources. An improved understanding of the soot nanoheterogeneity in airborne and combustion particles is likely to greatly influence PM2.5-related health and source apportionment research.