Аннотация:The mineralogy of the surface matter of asteroids can be judged using a qualitative interpretation of the reflectance spectra of these bodies. The features of the reflectance spectra (absorption bands) are wide enough for correct interpretation even at a low resolution of the recording device. It should be noted that the number of registrations of sublimation activity among primitive asteroids has been increasing recently. The emergence of a temporary exosphere affects the asteroid spectral characteristics. The reflectance spectra of 12 asteroids of the Main Belt, mainly of primitive type, have been obtained and analyzed. The aim of the research was to study the influence of the temporal exosphere on the correct determination of the spectral type of the asteroid. In addition, for asteroid 203 Pompeia, the spectral type has been determined for the first time(class C).