Photochemical smog is a resultant of the reaction among
NO 2, O 3 and peroxyacetyl nitrate in the presence of sunlight
Understanding Photochemical Smog Formation
Photochemical smog is a type of air pollution that is formed when sunlight reacts with certain chemicals in the atmosphere. Unlike traditional smog which is primarily caused by smoke and fog, photochemical smog is a modern problem linked to emissions from vehicles and industrial activities.
The formation of photochemical smog is a complex process involving several pollutants. Let's look at the key components and conditions required for its formation, as described in the options provided.
Key Components and Conditions for Photochemical Smog
Photochemical smog is primarily formed from the reaction of primary pollutants in the presence of sunlight. The main primary pollutants are:
- Nitrogen Oxides ($\text{NO}_\text{x}$), mainly Nitric Oxide ($\text{NO}$) and Nitrogen Dioxide ($\text{NO}_2$), emitted from burning fossil fuels (like in cars and power plants).
- Volatile Organic Compounds (VOCs), emitted from various sources including vehicles, industries, and vegetation.
These primary pollutants undergo chemical reactions driven by sunlight to form secondary pollutants, which are the main constituents of photochemical smog. These secondary pollutants include:
- Ozone ($\text{O}_3$)
- Peroxyacetyl Nitrate (PAN)
- Aldehydes
- Ketones
The presence of sunlight is absolutely essential. It provides the energy needed to initiate and drive the complex chemical reactions that convert primary pollutants into secondary pollutants like ozone and PAN.
A simplified look at the process involves:
- Nitric oxide ($\text{NO}$) is oxidized to nitrogen dioxide ($\text{NO}_2$).
- Nitrogen dioxide ($\text{NO}_2$) absorbs sunlight and breaks down into nitric oxide ($\text{NO}$) and a free oxygen atom ($\text{O}$).
- The free oxygen atom ($\text{O}$) combines with molecular oxygen ($\text{O}_2$) to form ozone ($\text{O}_3$).
- In the presence of VOCs, more complex reactions occur, leading to the formation of other pollutants, including Peroxyacetyl Nitrate (PAN). PAN is formed from reactions involving hydrocarbons, nitrogen oxides, and oxygen.
Therefore, the formation of photochemical smog requires Nitrogen Dioxide ($\text{NO}_2$), Ozone ($\text{O}_3$) (which is formed during the process), and Peroxyacetyl Nitrate (PAN), all in the presence of sunlight.
Analyzing the Options
Let's examine the given options based on our understanding:
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$\text{NO}_2$, $\text{O}_3$ and peroxyacetyl nitrate in the presence of sunlight
This option lists key components ($\text{NO}_2$, $\text{O}_3$, PAN) and the essential condition (sunlight) that are central to the formation of photochemical smog. While $\text{O}_3$ and PAN are products rather than initial reactants, they are the defining components of the resulting smog mixture, formed from initial reactants like $\text{NO}_\text{x}$ and VOCs under sunlight. This option accurately describes the composition and condition of photochemical smog.
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CO, $\text{O}_2$ and peroxyacetyl nitrate in the presence of sunlight
While Carbon Monoxide (CO) is an air pollutant, it is not a primary reactant in the formation of Ozone or PAN in the core photochemical smog reactions. Molecular oxygen ($\text{O}_2$) is a reactant in forming $\text{O}_3$ and PAN, but CO is not typically listed as a key initiating substance like $\text{NO}_\text{x}$ and VOCs for the smog process itself, although it can participate in atmospheric chemistry.
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CO, $\text{CO}_2$ and $\text{NO}_2$ at low temperature
This option lists CO, Carbon Dioxide ($\text{CO}_2$), and $\text{NO}_2$. $\text{CO}_2$ is a greenhouse gas but not a primary component of smog formation. More importantly, photochemical smog requires sunlight (high temperature conditions during the day are usually when smog is worst), not low temperature.
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high concentration of $\text{NO}_2$, $\text{O}_3$ and CO in the evening
This option lists some relevant pollutants ($\text{NO}_2$, $\text{O}_3$, CO). However, photochemical smog formation is heavily dependent on sunlight, which is present during the day, not typically in the evening when sunlight intensity decreases significantly.
Based on the analysis, the option that best describes the resultant mixture and condition associated with photochemical smog is the one mentioning $\text{NO}_2$, $\text{O}_3$, and peroxyacetyl nitrate in the presence of sunlight.
| Component/Condition | Role in Photochemical Smog |
|---|---|
| Nitrogen Oxides ($\text{NO}_\text{x}$, especially $\text{NO}_2$) | Primary pollutants, precursors for $\text{O}_3$ and PAN formation. |
| Volatile Organic Compounds (VOCs) | Primary pollutants, precursors for PAN and other secondary pollutants. |
| Sunlight | Essential energy source driving the photochemical reactions. |
| Ozone ($\text{O}_3$) | Major secondary pollutant and a key component of smog. |
| Peroxyacetyl Nitrate (PAN) | Major secondary pollutant and a key component of smog. |
Revision Table: Photochemical Smog Key Facts
| Feature | Description |
|---|---|
| Cause | Reaction of primary pollutants (NOx, VOCs) with sunlight. |
| Key Ingredients | NOx, VOCs, Sunlight. |
| Major Components (Resultant) | Ozone ($\text{O}_3$), Peroxyacetyl Nitrate (PAN), Aldehydes. |
| Required Condition | Sunlight (Photochemical reactions). |
| When does it occur? | Typically during sunny days, common in summer. |
Additional Information: Effects of Photochemical Smog
Photochemical smog has various harmful effects on health, vegetation, and materials.
- Health Effects: Ozone and PAN are strong irritants. They can cause respiratory problems, eye irritation, headaches, and exacerbate conditions like asthma.
- Vegetation Damage: Ozone can damage plant leaves, affecting growth and yield. PAN is also phytotoxic.
- Material Damage: Ozone can degrade materials like rubber, plastics, and fabrics.
Controlling emissions of $\text{NO}_\text{x}$ and VOCs is crucial to reducing the formation of photochemical smog.
Important Questions from Environmental pollution
Which of the following is NOT responsible for the degradation of our environment?
With reference to furnace oil, consider the following statements:
1. It is a product of oil refineries.
2. Some industries use it to generate power.
3. Its use causes sulphur emissions into environment.
Which of the statements given above are correct?
Why is there a concern about copper smelting plants?
1. They may release lethal quantities of carbon monoxide into environment.
2. The copper slag can cause the leaching of some heavy metals into the environment.
3. They may release sulphur dioxide as a pollutant.
Select the correct answer using the code given below.
Magnetite particles, suspected to cause neurodegenerative problems are generated as environmental pollutants from which of the following?
1. Brakes of motor vehicles
2. Engines of motor vehicles
3. Microwave ‘Stoves within homes
4. Power plants
5. Telephone lines
Select the correct answer using the code given below.
Considering the primary atmospheric roles and radiative forcing characteristics, which of the following gases is not typically categorized as a long-lived, well-mixed greenhouse gas contributing directly to the Earth's warming, but rather is known for its role in atmospheric aerosol formation and acid deposition?
