Identifying Greenhouse Gases & Ozone Depleting Substances

The question asks to identify substances that exhibit two key characteristics: they must be greenhouse gases and also ozone-depleting substances (ODS). We need to evaluate each option based on these criteria.

Greenhouse Gas Properties

Greenhouse gases trap heat in the Earth's atmosphere, contributing to global warming.

Ozone Depleting Substance Properties

Ozone-depleting substances are chemicals that break down the stratospheric ozone layer, which protects life on Earth from harmful ultraviolet radiation.

Option Analysis

A. CFC-11 (Trichlorofluoromethane)

• Greenhouse Gas: Yes, CFC-11 is a potent greenhouse gas, significantly contributing to global warming.
• Ozone Depleting Substance: Yes, CFC-11 is a major ODS, responsible for significant ozone layer depletion.
• Conclusion: Meets both criteria.

B. $CO_2$ (Carbon Dioxide)

• Greenhouse Gas: Yes, $CO_2$ is the primary greenhouse gas emitted through human activities.
• Ozone Depleting Substance: No, $CO_2$ does not deplete the ozone layer.
• Conclusion: Does not meet both criteria.

C. HCFC-22 (Chlorodifluoromethane)

• Greenhouse Gas: Yes, HCFC-22 is also a greenhouse gas, although less potent than CFCs.
• Ozone Depleting Substance: Yes, HCFC-22 is an ODS, but with a much lower ozone depletion potential compared to CFCs. It was used as a transitional substitute.
• Conclusion: Meets both criteria.

D. $N_2O$ (Nitrous Oxide)

• Greenhouse Gas: Yes, $N_2O$ is a significant greenhouse gas with a long atmospheric lifetime.
• Ozone Depleting Substance: Yes, $N_2O$ is recognized as an ozone-depleting substance, affecting stratospheric ozone.
• Conclusion: Meets both criteria.

Final Conclusion

Based on the analysis, the substances that are both greenhouse gases and ozone-depleting substances are CFC-11, HCFC-22, and $N_2O$. Therefore, options A, C, and D are correct.