We report on an all-optical sensor system that employs GaN/InGaN nanowire heterostructures (NWH) as optochemical transducers. When exposed to ultraviolet light, such NWHs emit green luminesce light. This photoluminescence (PL) is intense and temperature stable, and persists up to transducer temperatures well beyond 200°C. When exposed to oxidizing gases such as O3, NO2, and O2 the PL intensity decreases. At room temperature minimum detectable O3-, NO2-, and O2- concentrations are 50 ppb, 500 ppb and 100 ppm, respectively. Above their minimum detectable concentrations the O3, NO2 and O2 responses increase in a quasi-logarithmic manner up to a temperature-dependent saturation level. It is shown that the observed features can be explained within a model of Langmuir adsorption and surface recombination.