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 sphere of volume V is made of a material with lower density than water. While on Earth, it floats on water with its volume f1V (f1 < 1) submerged. On the other hand, on a spaceship accelerating with acceleration a < g (g is the acceleration due to gravity on Earth) in outer space, its submerged volume in water is f2V. Then:
A railway wagon (open at the top) of mass M1 is moving with speed v1 along a straight track. As a result of rain, after some time it gets partially filled with water so that the mass of the wagon becomes M2 and speed becomes v2. Taking the rain to be falling vertically and the water stationery inside the wagon, the relation between the two speeds v1 and v2 is :
Consider the following statements:
1. Distance between the longitudes becomes zero on North Pole and South Pole.
2. Distance between the longitudes is maximum on the Equator.
3. Number of longitudes is more than number of latitudes.
Which of the statements given above is/are correct?
One block of 2⋅0 kg mass is placed on top of another block of 3⋅0 kg mass. The coefficient of static friction between the two blocks is 0⋅2. The bottom block is pulled with a horizontal force F such that both the blocks move together without slipping. Taking acceleration due to gravity as 10 m/s2, the maximum value of the frictional force is :
