A model of key processes influencing the evolution of a hydrocarbon grain of an arbitrary size under astrophysical conditions corresponding to ionized hydrogen regions (HII regions) and supernova remnants is presented. The considered processes include aromatization and photodestruction, sputtering by electrons and ions, and shattering due to collisions between grains. The model can be used to simulate the grain size distribution and the aromatization degree during the evolution of HII regions and supernova remnants for a specified radiation field, relative velocity of gas and dust, etc. The contribution of various processes to the evolution of hydrocarbon dust grains for parameters typical for the interstellar medium of our Galaxy is pre-