Problem 2 - Chemistry in 30 days

Question

Photochemical oxidant PAN is formed (a) by action of oxides of nitrogen on hydrocarbons in the presence of sunlight (b) by action of carbon dioxides on the hydrocarbons in the presence of sunlight (c) by action of hydrogen sulphide on hydrocarbons in the presence of sunlight (d) by the action of \(\mathrm{SO}_{2}\) and hydrocarbons

Step-by-Step Solution

Answer

(a) by action of oxides of nitrogen on hydrocarbons in the presence of sunlight

Step 1: Understanding the Photochemical Reaction

We start with understanding that PAN, which stands for peroxyacetyl nitrate, is a photochemical oxidant formed in the atmosphere. Photochemical oxidants are typically formed through chemical reactions involving sunlight.

Step 2: Identifying Key Reactants

PAN is specifically formed through reactions involving nitrogen oxides (NOx), volatile organic compounds (VOCs), and sunlight. These reactants undergo a series of reactions driven by sunlight, leading to the formation of PAN.

Step 3: Analyzing the Options

(a) The action of oxides of nitrogen on hydrocarbons in the presence of sunlight perfectly matches our understanding of the reactants leading to PAN formation, as it involves NOx and hydrocarbons under sunlight. (b) Involves carbon dioxide, which is not a correct reactant for PAN formation. (c) Involves hydrogen sulfide, which is unrelated to PAN formation. (d) Involves sulfur dioxide, which is also not involved in the formation of PAN.

Step 4: Selecting the Correct Answer

Option (a) is the correct choice as it accurately describes the reaction of nitrogen oxides with hydrocarbons in the presence of sunlight, which leads to the formation of PAN.

Key Concepts

peroxyacetyl nitrate (PAN)

Peroxyacetyl nitrate, commonly abbreviated as PAN, is a significant photochemical oxidant found in the atmosphere. It is part of a group of chemicals known as peroxyacyl nitrates, which are secondary pollutants formed through complex chemical reactions.
Unlike primary pollutants, which are directly emitted from sources like vehicles or industrial facilities, PAN is not released directly into the air. Instead, it is formed through a series of reactions involving precursor pollutants.
Key elements for PAN production include nitrogen oxides (NOx) and volatile organic compounds (VOCs). Here’s how PAN is formed:

• Sunlight acts as a catalyst, initiating a reaction between NOx and VOCs.
• This interaction forms radicals, which are highly reactive atoms or molecules.
• These radicals undergo further reactions, resulting in PAN.

One of the main concerns regarding PAN is its impact on air quality and human health. As a photochemical smog component, PAN can cause respiratory problems and damage vegetation.
As a result, monitoring levels of PAN is crucial for managing air quality and mitigating its adverse effects on the environment.

nitrogen oxides (NOx)

Nitrogen oxides, commonly referred to as NOx, are a group of reactive gases composed of nitrogen and oxygen. Two of the most prevalent nitrogen oxides are nitric oxide (NO) and nitrogen dioxide (NO2).
These compounds play a vital role in the formation of photochemical smog and pollutants like PAN. Here are some essential facts about NOx:

• Sources of NOx include combustion processes like those in vehicles, power plants, and industrial activities.
• NOx emissions increase during burning of fossil fuels at high temperatures.
• In the presence of sunlight, NOx reacts with VOCs, leading to the formation of photochemical pollutants.

NOx has significant environmental and health impacts. It can contribute to environmental issues like acid rain, which harms aquatic systems and soil.

• Exposure to NOx can lead to respiratory problems and exacerbate conditions like asthma.
• It also plays a role in ground-level ozone formation, which has additional health impacts.

To address the concerns associated with NOx, it's essential to regulate emissions from major sources and promote cleaner technologies.

volatile organic compounds (VOCs)

Volatile organic compounds, or VOCs, are a large and diverse group of carbon-based chemicals that are volatile, meaning they easily vaporize into the air. VOCs are crucial to understanding photochemical oxidant formation like PAN.
Here’s what you need to know about VOCs:

• Sources of VOCs include emissions from vehicles, industrial processes, and even products like paints and solvents used in everyday life.
• Once in the atmosphere, VOCs can react with NOx and sunlight to contribute to the formation of secondary pollutants such as PAN and ozone.
• The diversity of VOCs means that different compounds can have varying levels of reactivity.

Importantly, certain VOCs can have direct adverse effects on health. Exposure to high levels of VOCs can lead to issues like headaches, dizziness, and long-term effects like liver or kidney damage.

• Control measures focus on reducing emissions from both industrial and consumer products.
• Efforts also involve setting safe exposure limits and improving indoor air quality.

Understanding and managing VOC emissions are crucial for improving air quality and reducing health risks associated with photochemical pollutants.