To explore the sensitive characteristics of gas molecules (SO, SO2, NO, NO2) on a Boron Nitride(BN) monolayer and Aluminum(Al) -doped Boron Nitride(BN) monolayer, the B3PLYP functional and 6-311G (d, p) basis set computations were utilized, Gaussian 09 and Nanotube Modeller (2018) programs utilized. Significantly, these gases contribute to the degradation of the environment. From three options of monolayer : the center of the ring, nitrogen atom, and bridge(B-N) , adsorption energy, distance, and charge transfer factors allowed us to choose the best location for adsorption. Various gas molecules (SO, SO2, NO, and NO2) have had chemical adsorptions on a Boron Nitride (BN) monolayer and Aluminum(Al)-doped Boron Nitride (BN) monolayer. There is no physical adsorption of NO gas in bridge(B-N) , NO2 in nitrogen atom for BN monolayer, and NO2 gas in Bridge for Aluminum(Al) -doped Boron Nitride(BN) monolayer. The findings of this work further show that following adsorption, there is a large amount of charge transfer between gas molecules and a Boron Nitride(BN) monolayer and an Aluminum(Al) -doped Boron Nitride(BN) monolayer, with the exception of one location where the adsorption energy is weak and the charge transfer is weak (NO gas /pristine Boron Nitride(BN). This means that a Boron Nitride(BN) monolayer and an Aluminum(Al)/doped Boron Nitride(BN) monolayer are more vulnerable to SO, SO2, NO, and NO2 adsorption than pristine and doped graphene, and that gas adsorption on the Aluminum(Al)/doped Boron Nitride(BN) monolayers is stronger to other gases. Furthermore, small gas molecule adsorption clearly modifies the band - gap and work function of a Boron Nitride(BN) and Aluminum(Al) -doped Boron Nitride(BN) monolayer to variable degrees. Our study will give theoretical guidance for practical implementations.