To explore the sensitive characteristics of tiny hazardous gas molecules (SO, SO2, NO, NO2) on a BN monolayer and C-doped BN monolayer, the B3PLYP functional and 6-311G (d, p) basis set computations were utilized. These gases contribute significantly to environmental deterioration. Adsorption energy, adsorption distance, and charge transfer factors all helped us choose the optimal adsorption location from three options: Center, N, and Bridge. The adsorption energy and electron localization function results indicate that various gas molecules (SO, SO2, NO, and NO2) are chemically adsorbed on a BN monolayer and C-doped BN. Our findings further show that following adsorption, there is a large amount of charge transfer between gas molecules and a BN monolayer and a C-doped BN monolayer, with the exception of one location where the adsorption energy is weak and the charge transfer is weak (NO/pristine BN). This means that an a BN monolayer and a C-doped BN monolayer are more vulnerable to SO, SO2, NO, and NO2 adsorption than pristine and doped graphene, and that gas adsorption on the C-doped BN monolayers is stronger to other gases. Furthermore, small gas molecule adsorption clearly modifies the band - gap and work function of a BN and C-doped BN monolayer to variable degrees. Our study will give theoretical guidance for practical implementations.