The optical coefficients of soot particles are measured in a flow-through optical cell at the wavelength 635 nm in a dry atmosphere and in an atmosphere saturated with water vapor. Two types of systems modeling atmospheric soot aerosols and differing in the degree of hygroscopicity of their particles are investigated and compared. One of the systems contains hydrophobic acetylene soot, and the other contains hydrophilic soot obtained through modification of the initial soot by vapors of glutaric acid. The results show that the optical properties of hydrophobic soot depend only slightly on the conditions of moistening, whereas the optical properties of hydrophilic soot change abruptly upon its moistening because of the formation of a hydrate shell. In the atmosphere saturated with water-vapor, the monomolecular layer of a hydrophilic organic substance leads to the watering of particles and an abrupt (more than twofold) increase in the cross section of light scattering. A further growth of the hydrophilic component of soot particles initiates the formation of micron drops on them, thus resulting not only in the natural effect of light scattering enhancement but also in a noticeable light absorption increase. In particular, a light absorption enhancement by a factor of 3.5 is characteristic of particles of enriched hydrophilic soot.