Soot restructuring experiments. Subjecting size-classified soot aerosol (240 nm) to singlecomponent vapors in a saturator reservoir partially filled with liquid or solid chemicals at room temperature produced no measurable increase in the particle mass. However, particle mobility diameter showed a small decrease (Fig. , 5% RH). As reported previously, such shrinkage of fractal soot after exposure to subsaturated vapors is indicative of capillary condensation, which places the condensate directly into junctions between the primary spheres, resulting in unbalanced forces that induce restructuring. The absence of a measurable particle mass gain suggests that the amount of condensate in our experiments was less than 2-3%, the precision of our mass measurement. Such a mass gain corresponds to a coating thickness of ~0.3 nm, if the condensate is distributed uniformly over the particle surface, or to a filling angle  1 = 35°, if the condensate is placed entirely into junctions (Fig. ).