Figs. 3 and 4 show the room temperature response of CuCrO2 nanocrystals and microcrystals to exposure of variable ozone concentration in the range of 50–200 ppm, respectively. It is evident that resistance of CuCrO2 nanocrystals and microcrystals ozone sensors decreased with the presence of ozone and the resistance almost recovered its original value when the ozone gas was turned off.