We report on a first-principles study of the electronic and transport properties of pristine, B-, C-, N-, O-doped blue phosphorene (BlueP) with the adsorption of gas molecules NH3, NO, NO2, CO, and CO2. The adsorption distances, adsorption energies, charge transfer, density of states (DOS), and transmission spectra of these gas molecules on molecules on doped as well as undoped BlueP is systematically investigated in this work. Our calculations show that the adsorption energy of NO and NO2 on pristine BlueP is the largest among the considered gas molecules, suggesting that pristine BlueP is more sensitive to these two gases. The results indicate that the pristine BlueP exhibits a weak sensitivity to NH3 and CO molecules, while B-doped BlueP strongly adsorbs NH3 and CO by way of strong chemical bonds. C-doped BlueP can enhance the sensitivity to NH3 gas molecules. The current-voltage (I-V) characteristics of the sensors are calculated using non-equilibrium the Green's function (NEGF) formalism. Theses sensors show characteristic responses along both the zigzag and the armchair directions depending on the type of the gas molecules.