Passivation by air, in theory, is possible, but it is not practical. 316L SS does not passivate by air very well as the upper layer of the metal needs to be prepared in order for the Cr O2 to form. CrO2 is the passivation layer at 20-25 Å. The oxygen in the air alone will not bond wih the Cr ions if the Cr ions are not easily accessible for oxidation. After all, it is Stainless Steel which means that most corrosion is inhibited. So in order to passivate with air, you would need sufficient Cr ions to bond with the oxygen and this may not form a uniform passivation layer. The Cr ions need to gravitate to the upper echelons of the metal, bond with the oxygen, and form a uniform layer to protect the rest of the metal. You cannot insure that all areas of the surface are completely passivated. This will leave pockets of unpassivated material which may corrode at a much faster rate as it is unprotected.
Additionally, you may or may not be able to measure the unequal passivated areas to know if the passivation was successful. It is unknown to me how long an air passivation sequence might take. It could be days, weeks, or months of exposure to the air for passivation to be effective. But is certainly is not minutes or hours.
Others may have different opinions
Nissan