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