Question

Which of the following gases is not responsible for photochemical smog? (a) Oxides of nitrogen (b) Hydrocarbons (c) Inert gases (d) Carbon monoxide

Short answer

Inert gases are not responsible for photochemical smog.

Step-by-step solution

Understanding Photochemical Smog

Photochemical smog is a complex type of air pollution that is caused by the reaction between sunlight and pollutants like hydrocarbons and nitrogen oxides. These reactions often produce secondary pollutants such as ozone.

Identifying the Gases Involved in Photochemical Smog Formation

Gases typically involved in the formation of photochemical smog include oxides of nitrogen and hydrocarbons. These gases react in the presence of sunlight to form smog.

Excluding Non-Contributing Gases

Inert gases do not react with other substances easily because of their stable electron configuration and thus do not contribute to the formation of photochemical smog.

Eliminating the Incorrect Options

Based on the information regarding the formation of photochemical smog, we can eliminate options (a) oxides of nitrogen, (b) hydrocarbons, and (d) carbon monoxide as these are known to play a role in smog formation, leaving us with option (c) inert gases as the correct answer.

Key concepts

Oxides of Nitrogen

Oxides of nitrogen, often referred to as NOx, are a group of gases primarily composed of nitric oxide (NO) and nitrogen dioxide (NO2). These pollutants originate mainly from vehicle exhausts, power plants, and industrial processes.

They play a significant role in atmospheric reactions that lead to the formation of photochemical smog, especially in urban areas. When exposed to sunlight, NOx gases interact with volatile organic compounds (VOCs) to produce ozone, which is a key component of smog.

• Nitric oxide reacts with ozone to form nitrogen dioxide.
• Nitrogen dioxide absorbs sunlight and breaks down to form nitric oxide and an oxygen atom, which can then react with molecular oxygen (O2) to produce ozone (O3).

It is important to regulate and monitor these gases because of their impact on air quality and human health. They can cause respiratory problems and aggravate conditions such as asthma.

Hydrocarbons

Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon. These include gases like methane (CH4) as well as a variety of volatile organic compounds that are associated with vehicle emissions, solvent use, and industrial processes.

In the context of photochemical smog, hydrocarbons are particularly significant because they react with oxides of nitrogen under the influence of sunlight to produce a range of secondary pollutants. These reactions can form various harmful constituents of smog, such as peroxyacetyl nitrate (PAN).

• Hydrocarbons can originate from both man-made and natural sources, including plants and vegetation.
• Some hydrocarbons are more reactive than others, with unsaturated hydrocarbons (like alkenes and alkynes) being more likely to engage in smog-forming reactions.

Reducing emissions of reactive hydrocarbons is essential for smog prevention and to safeguard environmental and human health.

Inert Gases

Inert gases, also known as noble gases, encompass a group of elements such as helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and often radon (Rn). These gases are characterized by their lack of reactivity due to having full valence electron shells.

Since they do not easily form chemical compounds, inert gases do not participate in the chemical reactions that lead to the formation of photochemical smog. Their stability makes them non-reactive in the presence of hydrocarbons, oxides of nitrogen, and sunlight.

• Inert gases are not typically associated with environmental harm in the context of air pollution.
• They are used in various applications requiring a non-reactive atmosphere, such as in light bulbs and welding processes.

Understanding the inert nature of these gases helps in identifying that they are not responsible for the creation of photochemical smog, as opposed to reactive gases like NOx and hydrocarbons.