Gasoline Direct Injection (GDI) engines have attracted considerable scholarly interest owing to their superior fuel efficiency and performance attributes nevertheless, the rise in particulate matter (PM) emissions constitutes a significant hurdle. This research investigates the effectiveness of hydrogen (H₂) supplementation as a strategy to alleviate PM emissions in a GDI engine operating on an E20 gasoline blend, utilizing various concentrations of H₂ (0.5, 1, and 2%). Transmission electron microscopy (TEM) was utilized to analyse the morphology of soot particles, with particular emphasis on primary particle size and carbon fringe length. The results indicate H2 supplementation significantly reduces PM formation by enhancing combustion efficiency. A discernible decrease in both primary particle size and fringe length was noted alongside increasing H2 concentrations, a phenomenon attributable to the enhanced oxidation of carbon precursors and the suppression of soot aggregation. Moreover, the integration of H2 promoted a more uniform fuel–air mixture, thereby reducing the likelihood of fuel-rich zones that are prone to soot production. These findings illuminate the dual role of H2 in mitigating emissions while maintaining engine performance, thus presenting a feasible pathway for achieving cleaner combustion in GDI engines. This academic inquiry contributes to the progression of sustainable automotive technologies by addressing the environmental challenges posed by particulate emissions.