Question

Which of the following statements are true? (1) Temperature inversion is caused by smog. (2) A product of photochemical smog is PAN.(3) \(\mathrm{O}_{3}\) is involved in photochemical smog. (4) \(\mathrm{O}_{3}\) layer is destroyed by fluorocarbons. (a) 1,2 and 3 (b) 1,2 and 4 (c) 2,3 and 4 (d) 1,3 and 4

Short answer

The correct answer is (c) 2, 3, and 4.

Step-by-step solution

Understanding Each Statement

First, we evaluate each statement individually. Statement (1) asserts that temperature inversion is caused by smog. Temperature inversion is actually a weather phenomenon that can trap smog, but it is not caused by smog itself. Thus, this statement is false. Statement (2) claims that a product of photochemical smog is PAN (peroxyacetyl nitrate), which is indeed a product of such smog. Therefore, this statement is true. Statement (3) relates to the involvement of \( \mathrm{O}_{3} \) (ozone) in photochemical smog, which is correct; ozone is a key component of photochemical smog. Thus, this statement is true. Statement (4) indicates that the ozone layer is destroyed by fluorocarbons, which is a well-known environmental impact of these substances. So, this statement is true.

Identifying True Statements

Based on the evaluation in the previous step, we can identify the true statements: - Statement (2) is true as PAN is a product of photochemical smog. - Statement (3) is true because \( \mathrm{O}_{3} \) is involved in photochemical smog. - Statement (4) is true because the ozone layer is damaged by fluorocarbons. Statement (1) was found to be incorrect, as temperature inversion is not caused by smog.Therefore, statements (2), (3), and (4) are true.

Choosing the Correct Option

From the analysis in the previous steps, the true statements are (2), (3), and (4). Among the given options, only option (c) lists statements 2, 3, and 4 as true. Therefore, option (c) is the correct choice.

Key concepts

Temperature Inversion

Temperature inversion is an interesting meteorological phenomenon where the normal temperature gradient in the atmosphere reverses. Typically, air temperature decreases with an increase in altitude. However, during a temperature inversion, a layer of warm air traps cooler air below it. This phenomenon is particularly common in valleys or urban areas and it prevents air pollutants, like smog, from dispersing into the atmosphere. Therefore, pollutants accumulate at the surface level, sometimes leading to poor air quality.

This is not caused by smog, though smog can be a consequence when pollutants are trapped. Think of temperature inversion as a lid, sealing pollutants close to the ground. When the conditions are right, such as clear skies and calm weather, the inversion forms, and smog becomes more common. Common effects include reduced visibility and respiratory problems in humans. Understanding this phenomenon helps to address air pollution effectively.

Peroxyacetyl Nitrate (PAN)

Peroxyacetyl Nitrate, or PAN, is a significant compound in the formation of photochemical smog. It belongs to the class of compounds known as peroxyacyl nitrates, which are secondary pollutants, meaning they are not emitted directly. Instead, they are formed in the atmosphere through chemical reactions.

PAN forms when nitrogen oxides \(NO\(_x\)\) and volatile organic compounds (VOCs) react in the presence of sunlight. It has the ability to cause eye irritation and respiratory problems.

• PAN is stable at lower temperatures, allowing it to move and distribute urban smog over large distances.
• It plays a crucial role in long-range pollution transportation.

Moreover, PAN's ability to affect ecosystems, plants, and human health makes it a vital topic in air quality studies. A deeper understanding of PAN can help in devising strategies to mitigate air pollution and protect public health.

Fluorocarbons

Fluorocarbons are compounds whose molecules contain fluorine and carbon. While they have various useful applications such as in refrigeration, nonstick coatings, and aerosol propellants, their release into the atmosphere has detrimental environmental impacts. Most notably, certain fluorocarbons are responsible for ozone layer depletion.

When fluorocarbons, often referred to as CFCs (chlorofluorocarbons), reach the upper atmosphere, they are broken down by ultraviolet rays, releasing chlorine atoms. These chlorine atoms catalyze reactions that destroy ozone molecules. Ozone, a vital component of the stratosphere, protects the Earth from harmful ultraviolet radiation.

The depletion of the ozone layer has grave consequences, including increased risks of skin cancer, cataracts, and adverse effects on crops and marine ecosystems. International efforts such as the Montreal Protocol have succeeded in drastically reducing the production and release of CFCs, demonstrating the power of global cooperation in addressing environmental issues.

Ozone Layer Depletion

Ozone layer depletion refers to the thinning of the Earth's stratosphere's protective layer, located around 10 to 30 miles above Earth's surface. This layer absorbs most of the Sun's harmful ultraviolet radiation. The depletion has been primarily attributed to human activities, especially the emission of halogen-containing compounds like CFCs and halons.

When these substances rise to the stratosphere, they release halogen atoms upon exposure to ultraviolet light, which then break down the ozone molecules. A striking consequence of ozone loss is the increased penetration of UV-B radiation to Earth's surface, leading to more cases of skin damage, eye disorders, and negative ecological effects. This has significant implications for all forms of life on Earth.

• Continuous monitoring and research are crucial to understanding and mitigating ozone depletion.
• Efforts like the Montreal Protocol have shown success, with signs of ozone recovery now more apparent.

Realizing the importance of the ozone layer underscores the necessity for continued global commitment to environmental preservation.