Question

Presence of which of the following in the atmosphere will cause the depletion of ozone? (a) Chlorofluoro carbons (b) \(\mathrm{Cl}_{2}\) (c) \(\mathrm{NO}\) (d) Any one of these

Short answer

(d) Any one of these

Step-by-step solution

Understanding Ozone Layer Depletion

The ozone layer is depleted primarily due to the presence of chemicals that release chlorine and bromine upon exposure to ultraviolet (UV) light. These chemicals are often referred to as ozone-depleting substances (ODS). Chlorofluorocarbons (CFCs) are well-known ODS as they release chlorine atoms when they break down, which contribute to the depletion of ozone.

Evaluating the Options

We need to identify which options among (a) Chlorofluoro carbons, (b) \( \text{Cl}_2 \), and (c) \( \text{NO} \) can cause ozone depletion. CFCs, once broken down in the atmosphere, release chlorine atoms that react with and deplete ozone. \( \text{Cl}_2 \) can also release chlorine atoms under UV radiation, contributing to ozone depletion. Nitric oxide (\( \text{NO} \)) can lead to ozone depletion through a series of chemical reactions in the atmosphere.

Analyzing Chemical Reactions

Chlorine atoms are highly reactive with ozone molecules. One chlorine atom can destroy thousands of ozone molecules through the following reaction series: \( \text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2 \); \( \text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2 \). Nitric oxide reacts with ozone in the presence of sunlight: \( \text{NO} + \text{O}_3 \rightarrow \text{NO}_2 + \text{O}_2 \). Both reactions contribute to ozone depletion.

Conclusion on Ozone Depletion

Chlorofluoro carbons (CFCs), chlorine (\( \text{Cl}_2 \)), and nitric oxide (\( \text{NO} \)) can all deplete ozone. Therefore, each of the substances listed in options (a), (b), and (c) can contribute to ozone layer depletion.

Key concepts

Chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs) are compounds made up of carbon, chlorine, and fluorine. Back in the day, they were widely used in the manufacturing of aerosol sprays, refrigeration, and air conditioning systems. However, CFCs have been identified as one of the main culprits behind the depletion of the ozone layer.
When CFCs are released into the atmosphere, they eventually rise up to the stratosphere. Here, they are broken down by ultraviolet rays from the sun, releasing chlorine atoms in the process. These chlorine atoms are highly reactive and can persist in the atmosphere for a long time, thus causing significant long-term damage.
The most concerning part is that a single chlorine atom can destroy thousands of ozone molecules by engaging in a repetitive cycle of reactions. This relentless attack on ozone molecules diminishes the ozone layer’s ability to shield the Earth from harmful ultraviolet radiation.

Chlorine (Cl_2)

Chlorine in the form of Cl_2 is notorious for its role in depleting the ozone layer. Upon exposure to UV light, Cl_2 releases chlorine atoms that react with ozone (O_3) in the stratosphere.
The chemical reactions involving Cl_2 and ozone can be summarized as follows:

• Chlorine molecule disintegration: Cl_2 + UV light → 2 Cl
• Ozone destruction: Cl + O_3 → ClO + O_2
• Regeneration of chlorine atoms: ClO + O → Cl + O_2

This cycle can occur numerous times, signifying the long-lasting and damaging impact of chlorine on the ozone layer. Each chlorine atom plays a pivotal role in this cycle, indicating how impactful Cl_2 presence can be in the atmosphere.

Nitric Oxide (NO)

Nitric oxide (NO) is another compound that contributes to ozone layer depletion but through a slightly different mechanism compared to CFCs and chlorines. NO is often released into the atmosphere from both natural processes such as lightning and human activities like combustion engines and industrial processes.
When NO reaches the stratosphere, it reacts with ozone in the following manner:

• Ozone reaction: NO + O_3 → NO_2 + O_2
  This reaction represents a direct pathway for ozone reduction, as the ozone molecule is converted into molecular oxygen. Nitric oxide initiates a series of reactions that consume ozone molecules, which under persistent conditions can lead to prolonged depletion.

This emphasizes the important role NO plays despite its differences from chlorine-releasing compounds.

Ozone-Depleting Substances (ODS)

Ozone-depleting substances (ODS) represent a group of human-made compounds that pose severe threats to the ozone layer. While the primary function of the ozone layer is to protect the Earth from harmful ultraviolet radiation, ODS lead to its deterioration by releasing reactive chemicals that damage ozone molecules.
Key players in ODS include:

• Chlorofluorocarbons (CFCs): Found in older refrigeration systems and aerosol sprays.
• Halons: Used in fire extinguishers.
• Methyl bromide: A pesticide used in agriculture.
• Carbon tetrachloride and tetrafluoroethane: Solvents and refrigerants.

The Montreal Protocol, an international treaty signed in 1987, aims to phase out the production of numerous ODS substances. This global initiative has seen substantial success in reducing ODS emissions, contributing significantly to the healing process of the ozone layer over recent decades.