We present the results of investigation of electron excitations in various carbon-based nanoscale systems in the process of photoionization. As a case in point, we consider a number of highly symmetric fullerenes, namely C, C and C, as well as aromatic hydrocarbons: benzene (CH) and coronene (CH). The calculations are performed within the model approach, based on the plasmon resonance approximation, and the ab initio framework as well. Analysis of the results demonstrates that the main contribution to the photoionization spectra of nanoscale carbon systems is due to collective excitations of delocalized electrons, known as plasmons. Results of the model-based calculations are in close agreement with those of the more accurate quantum-chemical calculations and correspond also to the existing experimental data.