The text states that the odor of ozone can be detected in concentrations as low as 10 ppb. In which one of the following samples/situations would you not be able to smell ozone.

1. 0.001 ppm ozone, the concentration of ozone in this classroom

2. 25 ppm ozone, a concentration reached in the Stratosphere

3. 0.115 ppm ozone, a concentration reached in the troposphere

4. 0.025 ppm ozone, the concentration of ozone in a copier room