Problem 31 - Chemistry in 30 days

Question

Which of the following is a secondary pollutant? (a) \(\mathrm{SO}_{2}\) (b) \(\mathrm{CO}_{2}\) (c) \(\mathrm{SO}_{3}\) (d) \(\mathrm{NH}_{3}\)

Step-by-Step Solution

Answer

\(\mathrm{SO}_{3}\) is a secondary pollutant.

Step 1: Understand Primary vs Secondary Pollutants

Primary pollutants are emitted directly from a source, while secondary pollutants are not directly emitted but form in the atmosphere when primary pollutants react. Examples of primary pollutants are \(\mathrm{SO}_{2}\), \(\mathrm{CO}_{2}\), and \(\mathrm{NH}_{3}\).

Step 2: Analyze the Options

Given options are \(\mathrm{SO}_{2}\), \(\mathrm{CO}_{2}\), \(\mathrm{SO}_{3}\), and \(\mathrm{NH}_{3}\). Identify if any of these form from reactions in the atmosphere. \(\mathrm{SO}_{3}\) often forms from the oxidation of \(\mathrm{SO}_{2}\) in the air, indicating it is a secondary pollutant.

Step 3: Identify the Correct Answer

From the analysis, \(\mathrm{SO}_{3}\) is not directly emitted by common sources but typically forms through chemical reactions involving \(\mathrm{SO}_{2}\). Thus, \(\mathrm{SO}_{3}\) is a secondary pollutant.

Key Concepts

Primary Pollutants

Primary pollutants are pollutants that are emitted directly into the atmosphere from identifiable sources. These sources can include both human activities and natural occurrences. Common examples of primary pollutants include sulfur dioxide \(\mathrm{SO}_{2}\), carbon dioxide \(\mathrm{CO}_{2}\), and ammonia \(\mathrm{NH}_{3}\). Each of these is released into the air directly through various processes:

• Sulfur dioxide (\(\mathrm{SO}_{2}\)): Released from the burning of fossil fuels by power plants, industrial facilities, and vehicles.
• Carbon dioxide (\(\mathrm{CO}_{2}\)): Emitted during the combustion of organic materials, like fossil fuels, oil, natural gas, and coal.
• Ammonia (\(\mathrm{NH}_{3}\)): Released from agricultural activities, livestock waste, and industrial processes.

These pollutants can lead to various environmental and health issues when present in high concentrations. They play a crucial role in forming secondary pollutants through complex chemical reactions in the atmosphere.

Atmospheric Reactions

Atmospheric reactions refer to the chemical processes that occur in the Earth's atmosphere, leading to the transformation of primary pollutants into secondary pollutants. These reactions are typically catalyzed by sunlight and involve photochemical processes, oxidation, and hydrolysis.

• Photochemical Reactions: Sunlight acts on pollutants, transforming them into new chemical substances.
• Oxidation Processes: This involves the addition of oxygen or the removal of hydrogen from a substance, resulting in a new reactive species that further reacts to form secondary pollutants.
• Hydrolysis: Water interacts with atmospheric chemicals, leading to breakdown and formation of different compounds.

Through these reactions, substances like sulfur dioxide can transform into sulfur trioxide \(\mathrm{SO}_{3}\), contributing to environmental phenomena such as acid rain.

Oxidation of Sulfur Dioxide

The oxidation of sulfur dioxide \(\mathrm{SO}_{2}\) is a key process in atmospheric chemistry that leads to the formation of secondary pollutants, particularly sulfur trioxide \(\mathrm{SO}_{3}\). This process involves a series of reactions usually catalyzed by the presence of atmospheric oxygen and water.

The Basic Reaction

Sulfur dioxide is oxidized to sulfur trioxide in the presence of catalyst like particulate matter or under specific atmospheric conditions.\[\mathrm{2\,SO_{2} \, + \, O_{2} \, \longrightarrow \, 2\,SO_{3}}\]The sulfur trioxide then reacts further with water in the atmosphere to form sulfuric acid \(\mathrm{H_{2}SO_{4}}\), which is a major component of acid rain.

Environmental Impact

The oxidation of \(\mathrm{SO}_{2}\) not only contributes to acid rain, impacting ecosystems and human structures, but it can also affect human health by aggravating respiratory conditions. Understanding these conversions is crucial to addressing air pollution and its wide-ranging effects.