Temporal transformation of the particle size spectrum of submicron and coarsely dispersed fractions of aerosols during formation and evolution of optically dense winter haze has been studied. Results have been obtained by the inverseuproblem method from the data of experimental measurements of spectral dependence of the aerosol extinction coefficient within the wavelength range from 0.44 to 3.9 mm. The observed temporal behavior of absolute air humidity under conditions of constantly high (more than 95%) relative humidity was shown to correlate with the dynamics of the main integral microstructure characteristics of the aerosol accumulative fraction, namely, total geometric cross section, particle number density, and particle volume concentration. Variations in the modal radius and halfwidth of the accumulative particle size distribution function were synchronous.