Question

Photochemical smog occurs in warm, dry and sunny climate. One of the following is not amongst the components of photochemical smog, identify it. (A) \(\mathrm{NO}_{2}\) (B) \(\mathrm{O}_{3}\) (C) \(\mathrm{SO}_{2}\) (D) Unsaturated hydrocarbon

Short answer

The component that is not part of photochemical smog is (C) \(\mathrm{SO}_{2}\) (Sulfur dioxide), as it is more associated with industrial processes and other sources of sulfur-containing compounds.

Step-by-step solution

Review the Components of Photochemical Smog

Photochemical smog, as mentioned above, is the result of sunlight reacting with certain chemicals in the atmosphere. The major components of photochemical smog include: 1. Nitrogen oxides (primarily \(\mathrm{NO}\) and \(\mathrm{NO}_{2}\)) 2. Ozone (\(\mathrm{O}_{3}\)) 3. Peroxyacetyl nitrates (PANs) 4. Aldehydes, such as formaldehyde 5. Volatile organic compounds (VOCs), like unsaturated hydrocarbons.

Identify the Component Not Associated with Photochemical Smog

Now, let's examine the given options for the components and identify which one does not belong to the list of photochemical smog components: (A) \(\mathrm{NO}_{2}\): Nitrogen dioxide is one of the major components of photochemical smog, as it reacts with sunlight to form \(\mathrm{O}_{3}\). (B) \(\mathrm{O}_{3}\): Ozone is also a key component of photochemical smog, as it is produced through the reactions involving sunlight, nitrogen oxides, and VOCs. (C) \(\mathrm{SO}_{2}\): Sulfur dioxide is not considered a major component of photochemical smog. Although it is an air pollutant, it is more associated with industrial processes and other sources of sulfur-containing compounds. (D) Unsaturated hydrocarbon: Unsaturated hydrocarbons are classified as volatile organic compounds (VOCs), and they are part of the photochemical smog formation process.

Choose the Correct Option

By comparing the given options with the list of the major components of photochemical smog, we can determine that the correct answer is: (C) \(\mathrm{SO}_{2}\): Sulfur dioxide is not among the components of photochemical smog.

Key concepts

Nitrogen Oxides

Nitrogen oxides, commonly referred to as NOx, are a critical component in the formation of photochemical smog. These compounds primarily include nitric oxide (NO) and nitrogen dioxide (NO₂).
These gases are produced from vehicles, power plants, and industrial activities when nitrogen in the air reacts with oxygen at high temperatures.
Their role in smog formation is quite pivotal:

• When NOx emissions are released into the atmosphere, they interact with sunlight and other substances.
• This interaction results in the formation of ozone, which is a key ingredient of photochemical smog.
• In sunny and warm conditions, the reaction is accelerated, leading to higher concentrations of smog components in the air.

Understanding the behavior of nitrogen oxides helps in tackling air pollution issues effectively.
Reducing NOx emissions can significantly decrease the formation of harmful air pollutants like smog and acid rain.

Ozone

Ozone plays a dual role in our atmosphere. It exists both at ground level and in the upper atmosphere, impacting environmental and human health in different ways. At ground level, ozone is not emitted directly into the air, but is created by chemical reactions between NOx and VOCs in the presence of sunlight. This forms a substantial part of photochemical smog.
Here's how ozone contributes to smog:

• As a secondary pollutant, it arises from reactions fueled by sunlight, unlike primary pollutants which are directly emitted.
• Ground-level ozone can cause a range of adverse effects, including respiratory issues and damage to plants and ecosystems.
• It's a key air quality concern, especially in urban areas with dense traffic and industrial activities.

Efforts to improve air quality often focus on reducing ozone precursors, NOx and VOCs, to mitigate health impacts and environmental degradation.

Volatile Organic Compounds

Volatile Organic Compounds (VOCs) include a variety of chemicals, including unsaturated hydrocarbons, that readily evaporate at room temperature. These compounds are crucial in the photochemical smog formation process.
VOCs can come from both natural sources and human activities, such as:

• Burning of fossil fuels and biomass, commonly found in car emissions.
• Industrial processes and chemical solvents, including paints and cleaning supplies.
• Natural sources like vegetation, which release terpenes and isoprene.

When VOCs mix with NOx in the presence of sunlight, they undergo complex chemical reactions, leading to smog formation.
These reactions not only produce ozone but also create other harmful pollutants like peroxyacetyl nitrates (PANs) and aldehydes.
Understanding and controlling VOC emissions is a vital step in reducing photochemical smog and improving air quality in densely populated urban areas.