SnO2 and ZnO and metal oxide nanowires were synthesized by vapor transport process in a horizontal tube furnace. The peculiar characteristic of these materials is the emission of visible photoluminescence (PL) when they are excited with UV light. The visible photoluminescence of tin and zinc oxide nanowires is quenched by nitrogen dioxide at ppm level in a fast (time scale order of seconds) and reversible way. Besides, the response seems highly selective toward humidity and other polluting species, such as CO and NH3. We believe that adsorbed gaseous species that create surface states can quench PL by creating competitive nonradiative paths.