Problem 23 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is not regarded as a pollutant? (a) \(\mathrm{CO}_{2}\) (b) \(\mathrm{O}_{3}\) (c) \(\mathrm{NO}_{2}\) (d) hydrocarbons

Step-by-Step Solution

Answer

(a) \( \mathrm{CO}_{2} \) is not regarded as a pollutant.

Step 1: Understanding Pollutants

Pollutants are substances that contaminate the environment. Common pollutants include gases like carbon dioxide, ozone, nitrogen dioxide, and hydrocarbons. We need to identify which of these is not typically regarded as a pollutant.

Step 2: Analyze Each Substance

- **Carbon Dioxide ( MathType):** Generally a greenhouse gas contributing to global warming. - **Ozone ( MathType):** Considered a pollutant in the troposphere where it forms smog. - **Nitrogen Dioxide ( MathType):** A major air pollutant contributing to smog and acid rain. - **Hydrocarbons:** Organic compounds that can be pollutants contributing to smog formation.

Step 3: Identify the Exception

Carbon dioxide is a necessary part of the life cycle and not generally deemed a pollutant at levels occurring naturally in the atmosphere, unlike the other options that are directly harmful pollutants in small concentrations.

Key Concepts

Air Pollutants

Air pollutants are substances that, when present in the air in significant amounts, can cause harm to humans, animals, plants, or even entire ecosystems. They come from both natural and human activities and can vary greatly in their effects and their persistence in the atmosphere.

Some common air pollutants include:

• **Nitrogen Dioxide (NO2):** A reddish-brown gas with a pungent smell, contributing to the formation of smog and acid rain. It can cause respiratory issues and is emitted from vehicles and industrial processes.
• **Ozone (O3) at the Ground Level:** Although beneficial in the upper atmosphere, at ground level, it forms part of smog and can cause respiratory problems.
• **Hydrocarbons:** Organic compounds that can evaporate into the air and react with sunlight to form harmful ground-level ozone, a key component of smog.

It's important for environmental chemistry to monitor and control these pollutants to protect health and the environment.

Greenhouse Gases

Greenhouse gases are naturally occurring and human-made gases that trap heat in the atmosphere, leading to the greenhouse effect which warms the Earth. While essential for maintaining a habitable climate, excessive amounts can lead to global warming.

Some key greenhouse gases include:

• **Carbon Dioxide (CO2):** Despite being naturally present and essential for plant life through photosynthesis, its levels have increased significantly due to fossil fuel combustion and deforestation.
• **Methane (CH4):** More effective at trapping heat than CO2 but less abundant. It is released from agriculture, landfill decomposition, and oil and gas operations.
• **Nitrous Oxide (N2O):** Released from agricultural and industrial activities as well as combustion of fossil fuels and solid waste.

Understanding how these gases work and their sources can help us combat climate change by reducing emissions and creating more sustainable practices.

Ozone Layer

The ozone layer is a crucial part of Earth's stratosphere that absorbs most of the Sun's harmful ultraviolet (UV) radiation. This shielding protects living organisms on Earth from the potential damage caused by excessive UV exposure.

Here are some key points about the ozone layer:

• **Composition:** The layer is made up of ozone (O3) molecules. These molecules are formed when UV light strikes oxygen molecules (O2), splitting them into individual oxygen atoms that then combine with other oxygen molecules.
• **Ozone Depletion:** Certain man-made chemicals, like chlorofluorocarbons (CFCs), once used in air conditioning, refrigeration, and aerosol propellants, have been known to deplete the ozone layer, causing holes.
• **Protection Measures:** International efforts like the Montreal Protocol have successfully reduced the use of ozone-depleting substances, aiding in the recovery of the ozone layer.

Protecting the ozone layer is essential for sustaining life by ensuring that harmful UV radiation does not reach the Earth's surface. Ensuring this means following international guidelines to continue minimizing pollutants that cause its depletion. This critical environmental chemistry issue showcases how global cooperation can make a positive impact.