Partial discharge (PD) in electrical equipment, such as air switchgear, can lead to insulation degradation and, ultimately, equipment failure. Monitoring PD is crucial for preventing failures and ensuring the reliability of power systems. This study proposes an online monitoring method for PD in air switchgear based on characteristic gases generated by insulation defects. A novel gas detection system is developed that identifies gases released during partial discharge events. The system employs gas sensors to detect specific gases like acetylene (C2H2), methane (CH4), and ethylene (C2H4), which are associated with PD. The system's performance was evaluated in both laboratory conditions and in-field testing, showing that it successfully detected PD events with high accuracy. The research demonstrates the potential for real-time, non-invasive monitoring of PD to improve the reliability and safety of electrical switchgear.