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

Option (a) \(\mathrm{CO}_{2}\) is not regarded as a pollutant in the options given.

Step 1: Identify the Types of Pollutants

Pollutants are typically substances introduced into the environment causing adverse effects. Common pollutants include gases like \(NO_2\) and hydrocarbons, which contribute to smog and health problems. \(O_3\), while beneficial in the upper atmosphere, is considered a pollutant at ground level.

Step 2: Consider Carbon Dioxide

\(CO_2\) is often discussed concerning climate change because it contributes to the greenhouse effect, which raises Earth's temperatures. However, it is a naturally occurring component of Earth's atmosphere and is not considered a pollutant in the same sense as other harmful substances.

Step 3: Determine Which Option Is Not a Pollutant

Among the given options, only \(CO_2\) is not regarded as a pollutant in the context of contributing directly to environmental harm through toxic or smog-forming effects, unlike the others listed.

Key Concepts

Pollutants

Pollutants are substances introduced into the environment that cause harm, either to our health or the ecosystem. These substances can be in the form of gases, liquids, or solids. Several common pollutants include nitrogen dioxide ( NO_2 ) and hydrocarbons. These pollutants are known for their role in the formation of smog and potential adverse health effects.

It's important to note that substances like ozone ( O_3 ) can have dual roles in our atmosphere: beneficial in the stratosphere, where they block harmful UV radiation, but considered pollutants at ground level due to their role in respiratory issues and contributing to smog formation.

When assessing whether a substance is a pollutant, it's crucial to consider its source, concentration, and effects. A substance may not be inherently harmful but can become a pollutant when present in large quantities or under certain conditions.

Greenhouse Effect

The greenhouse effect is a natural phenomenon that warms the Earth's surface. It occurs when the sun's energy reaches Earth, where it is absorbed and then radiates back as heat. Certain gases in our atmosphere, such as carbon dioxide ( CO_2 ), trap this heat, preventing it from escaping back into space. This trapped heat increases the Earth’s temperature, making the planet habitable for life.

However, human activities, particularly the burning of fossil fuels, have increased the concentration of these greenhouse gases, particularly CO_2 . This enhancement of the greenhouse effect is causing global temperatures to rise, contributing to climate change.

Although CO_2 is crucial for maintaining life-friendly temperatures, its role as a significant contributor to climate change creates a complex narrative. While not a conventional pollutant like chemicals that directly cause harm to life forms, its environmental impact is substantial and significant.

Smog

Smog is a form of air pollution that is a combination of smoke and fog, typically found in urban areas. It is largely the result of reactions between sunlight and pollutants such as NO_2 and volatile organic compounds (VOCs), leading to the formation of ozone ( O_3 ) at ground level.

Smog is particularly problematic because it reduces visibility and has significant health impacts. It can cause or exacerbate respiratory problems, cardiovascular diseases, and other health conditions. The elderly, children, and individuals with pre-existing health conditions are especially vulnerable to smog-related health issues.

The presence of smog indicates high levels of pollution, which can originate from vehicle emissions, industrial processes, and other combustion activities. Managing and reducing the pollutants that cause smog is crucial for improving air quality and protecting public health.