Problem 7 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The primary pollutant that leads to photochemical smog is: (a) acrolein (b) nitrogen oxides (c) ozone (d) sulphur dioxide

Step-by-Step Solution

Answer

(b) nitrogen oxides

Step 1: Understanding Photochemical Smog

Photochemical smog is a type of air pollution produced when sunlight interacts with certain airborne chemicals. The primary constituents needed for the formation of photochemical smog are pollutants that react under sunlight to form secondary pollutants, notably ozone.

Step 2: Identifying Key Pollutants

The main pollutants involved in the formation of photochemical smog include volatile organic compounds (VOCs) and nitrogen oxides (NOx). Nitrogen oxides are crucial because they react with VOCs in the presence of sunlight to create ozone and other smog components.

Step 3: Analyzing the Options

Review the options given: (a) acrolein, (b) nitrogen oxides, (c) ozone, (d) sulphur dioxide. Acrolein and sulphur dioxide are not primary contributors to photochemical smog. Ozone is a result of the reaction, not a primary pollutant that leads to smog. Nitrogen oxides, on the other hand, act as precursors in the formation of smog.

Step 4: Choosing the Correct Answer

Since nitrogen oxides are essential in the formation of photochemical smog, the correct answer is (b) nitrogen oxides.

Key Concepts

Air Pollution

Air pollution is a significant environmental issue that affects the health and quality of life for people worldwide. It results from the release of harmful substances into the atmosphere, which can come from various sources.
Some of the most common contributors to air pollution include:

• Vehicle emissions
• Industrial discharges
• Burning of fossil fuels like coal and oil
• Natural events like wildfires and volcanic eruptions

Each of these sources releases pollutants such as carbon monoxide, sulfur dioxide, particulate matter, and volatile organic compounds (VOCs). These pollutants can have various effects on human health, such as respiratory problems, cardiovascular diseases, and exacerbated asthma symptoms.
Beyond health issues, air pollution also significantly impacts the environment by contributing to problems like acid rain, ozone layer depletion, and climate change.

Nitrogen Oxides

Nitrogen oxides (NOx) are a group of highly reactive gases that play a crucial role in the air pollution story, particularly in the formation of photochemical smog. They are formed primarily during combustion processes.
Common sources include:

• Exhaust from motor vehicles
• Emissions from power plants
• Industrial facilities

These gases are not only involved in the production of ground-level ozone but are also significant contributors to other environmental issues like acid rain and nutrient pollution in water systems.

The Role of Nitrogen Oxides in Smog Formation

When nitrogen oxides are released into the atmosphere, they can react with volatile organic compounds (VOCs) in the presence of sunlight. This photochemical reaction leads to the formation of ground-level ozone and other harmful pollutants. Nitrogen oxides are thus a critical "precursor" in the development of photochemical smog.

Ozone Formation

Understanding ozone formation is vital for grasping the intricacies of photochemical smog. Ozone at the ground level is not directly emitted but forms when nitrogen oxides (NOx) and volatile organic compounds (VOCs) chemically react under sunlight.
This process can be simplified as follows:

• Step 1: Sunlight causes nitrogen oxides to break down, releasing oxygen atoms.
• Step 2: These oxygen atoms combine with molecular oxygen ( O_2 ) to create ozone ( O_3 ).

Importance of Ozone Location

Ozone occurs naturally in the Earth's stratosphere, where it forms a protective layer that blocks harmful ultraviolet radiation from the sun. However, when it forms closer to the ground, it becomes a health hazard, responsible for issues like respiratory problems and smog.
Therefore, ground-level ozone is a significant concern in urban areas where vehicle emissions and sunlight are abundant. Understanding its formation is crucial for developing strategies to reduce smog and protect both human health and the environment.