As overshooting climate targets becomes a distinct possibility, various scenarios are proposed for bringing the global temperature down quickly. Most scenarios rely on implementing carbon dioxide removal or even invoke use of various geoengineering approaches. Yet, curbing emissions of soot may offer the greatest potential for slowing down climate change because of significantly shorter lifetime of soot relative to carbon dioxide and other greenhouse gases. A product of incomplete combustion, soot is ubiquitous worldwide and can be present in more than half of ambient particles in highly polluted atmospheric environments. Due to its strong light absorption and poor light scattering, soot is a major global warming agent, and exposure to soot negatively affects human health. In the atmosphere, aging of soot through interactions with other trace chemicals significantly alters its composition and morphology. As a result, soot atmospheric lifetime, its deposition in the human respiratory tract, and its direct and indirect climate forcing become modified, making the knowledge of soot aging pathways paramount for accurate predictions of its impacts. Whereas the importance of rigorous treatment of particle morphology in predicting soot impacts has been clearly demonstrated, the role of morphology in evaluating its aging rate has remained elusive. Soot particles formed by fossil fuel combustion are lacey and hydrophobic, as illustrated in Fig. . The hydrophobic soot particles are not scavenged from the atmosphere as easily as other aerosols and show little morphological variability between dry and humid environments. However, after mixing with water-soluble chemicals during atmospheric aging, soot particles can take up water and undergo compaction, as demonstrated in laboratory studies using both individual trace gas chemicals and mixtures of condensable chemicals produced through oxidation of precursor compounds. Field studies conducted in urban environments have closely associated the morphological compaction of soot particles with the extent of their aging, and the presence of a thick coating has become a criterion for switching from fractal to compact morphology when predicting the impacts of soot in aerosol models. Thus, the observation of compact soot particles lacking visible coatings reported by a field study conducted in a remote marine free troposphere and supported by cloud chamber experiments was rather unexpected. This compaction was attributed to cloud processing, where soot particles underwent a cloud droplet activation-evaporation cycle.