The paper presents the structural stability and electronic properties of various gas molecules AGaNNR with a width (N _a ) of 5, 7 and 9. Width dependency is analysed using density functional theory (DFT). The electronic properties of all bare AGaNNR configurations exhibit the semiconducting nature. The reduction in the band gap has been noticed for selective edge adsorption. Due to interactions between CO ₂ , CO, NO ₂ , NO and O ₂ gas molecules, AGaNNR turns its nature from semiconducting to metallic. Based on binding energy/adsorption calculations, O ₂ -AGaNNR configuration found to be the most stable and energetically favoured configuration as compared to other configurations. CO ₂ , CO, NO ₂ , NO and O ₂ gases are selected as the targeted gas molecules and their adsorption on AGaNNRs have been selected for different configurations. The sensing capabilities of various harmful environmental gases are investigated and compared with width dependency. The selectivity of CO ₂ /O ₂ of AGaNNR configuration is the most preferred one amongst all considered configurations. Due to the lower recovery time, CO ₂ -AGaNNR configuration can be considered for fast sensing devices. The proposed device shows the potential for futuristic low power and high speed nano-scale sensor device applications.