Which atmospheric gas is primary ingredient of photochemical smog?
Ozone
Understanding Photochemical Smog Composition
Photochemical smog is a type of air pollution that forms when sunlight reacts with nitrogen oxides (NOx) and at least one volatile organic compound (VOC) in the atmosphere. These pollutants come from sources like vehicles, power plants, and industrial activities. Understanding the components of photochemical smog is crucial for addressing air quality issues.
Key Ingredients of Photochemical Smog
The formation of photochemical smog is a complex series of chemical reactions. Several harmful substances are produced during this process, but one gas plays a central role and is often considered a primary ingredient:
- Nitrogen Oxides (NOx)
- Volatile Organic Compounds (VOCs)
- Sunlight
- Ozone ($\text{O}_3$)
- Peroxyacetyl Nitrate (PAN)
- Aldehydes
While NOx and VOCs are the primary precursors that react, ozone ($\text{O}_3$) is a major component and a characteristic indicator of photochemical smog. It is formed through reactions involving NOx and VOCs in the presence of sunlight.
The Role of Ozone in Photochemical Smog
Ground-level ozone, which is different from the protective stratospheric ozone layer, is a harmful air pollutant and a primary component of photochemical smog. Its formation is driven by sunlight energy breaking down nitrogen dioxide ($\text{NO}_2$) into nitric oxide (NO) and a free oxygen atom (O). This free oxygen atom then combines with molecular oxygen ($\text{O}_2$) to form ozone ($\text{O}_3$).
The presence of VOCs in the atmosphere complicates this process and leads to the accumulation of ozone and other harmful pollutants like PAN. High concentrations of ground-level ozone in photochemical smog can cause respiratory problems, damage vegetation, and harm materials.
| Component/Precursor | Source | Role in Smog |
|---|---|---|
| Nitrogen Oxides (NOx) | Combustion (vehicles, power plants) | Reactants; initiate ozone formation chain reactions |
| Volatile Organic Compounds (VOCs) | Combustion, solvents, vegetation | Reactants; enhance ozone formation and create other pollutants |
| Sunlight | Solar radiation | Energy source driving chemical reactions |
| Ozone ($\text{O}_3$) | Formed during reactions | Primary ingredient; harmful respiratory irritant |
| Peroxyacetyl Nitrate (PAN) | Formed during reactions | Harmful eye irritant; plant damage |
Therefore, while several substances are involved in photochemical smog, ozone ($\text{O}_3$) is the most characteristic and harmful component that is formed during the process, making it a primary ingredient.
Revision Table: Photochemical Smog Key Points
| Term | Description |
|---|---|
| Photochemical Smog | Air pollution from reactions of NOx, VOCs, and sunlight. |
| Precursors | Substances that react to form smog (NOx, VOCs). |
| Primary Ingredient (Ozone) | Major harmful component formed during the reactions ($\text{O}_3$). |
| Harmful Effects | Respiratory issues, plant damage, eye irritation. |
Additional Information on Photochemical Smog and Ozone
Photochemical smog is also known as Los Angeles smog. It is different from London-type smog (sulfurous smog) which is primarily caused by burning coal and involves sulfur dioxide ($\text{SO}_2$). Photochemical smog pollution tends to be worse during sunny, warm weather, especially in urban areas with high traffic density.
Ground-level ozone is considered a secondary pollutant because it is not directly emitted but formed through chemical reactions in the atmosphere. Despite being a secondary pollutant, its high concentration and harmful effects make it a primary ingredient of the resulting smog mixture.
Controlling photochemical smog requires reducing the emissions of its precursors, mainly NOx and VOCs, from vehicles and industries.
Important Questions from Miscellaneous
A stone is thrown horizontally from the top of a 20 m high building with a speed of 12 m/s. It hits the ground at a distance R from the building. Taking g = 10 m/s2 and neglecting air resistance will give :
A mass is attached to a spring that hangs vertically. The extension produced in the spring is 6 cm on Earth. The acceleration due to gravity on the surface of the Moon is one-sixth of its value on the surface of the Earth. The extension of the spring on the Moon would be:
Directions: Each item in this section consists of a sentence with an underlined word followed by four words (a), (b), (c), and (d). Select the option that is opposite in meaning to the underlined word and mark your response in your Answer Sheet accordingly.
The deluge affected the population.The major source of vitamins and minerals for vegetarians is
Which of the following statements about the Deccan Riots Commission is/are correct?
1. The Commission did not hold enquiries in the districts which were not affected.
2. The Commission did record the statements of ryots, sahukars and eye-witnesses.
Select the correct answer using the code given below:
