Problem 22 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a primary pollutant? (a) \(\mathrm{PAN}\) (b) aldehydes (c) \(\mathrm{CO}\) (d) \(\mathrm{H}_{2} \mathrm{SO}_{4}\)

Step-by-Step Solution

Answer

(c) CO is a primary pollutant.

Step 1: Understand Primary Pollutants

Primary pollutants are those pollutants that are emitted directly from a source into the atmosphere. They are not formed in the atmosphere but are emitted in the form they exist.

Step 2: Identify Characteristics of PAN

PAN (Peroxyacetyl nitrate) is formed by the reaction of volatile organic compounds (VOCs) with oxygen and nitrogen oxides under sunlight. As it is formed through reactions in the atmosphere, it is considered a secondary pollutant.

Step 3: Analyze Aldehydes

Aldehydes, such as formaldehyde, can be emitted directly into the atmosphere from sources such as combustion but are also formed as secondary pollutants from VOC reactions. They can fit both primary and secondary classification depending on the context.

Step 4: Consider Carbon Monoxide (CO)

Carbon monoxide is directly emitted from sources like vehicle exhausts and industrial processes. It is released directly into the atmosphere and does not form in the atmosphere from other reactions, making it a known primary pollutant.

Step 5: Evaluate Sulfuric Acid (H2SO4)

H2SO4 is a secondary pollutant since it forms in the atmosphere by the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3), which subsequently reacts with water vapor to form sulfuric acid.

Step 6: Determine the Primary Pollutant

Based on the analysis, the primary pollutant is the one that is emitted directly into the atmosphere without requiring atmospheric reactions to form. Among the given options, CO is directly emitted and is a primary pollutant.

Key Concepts

Carbon Monoxide Emission

Carbon monoxide (CO) is a colorless, odorless gas that is produced when carbon-containing fuels such as gasoline, natural gas, or wood do not burn completely. This incomplete combustion results in the release of CO directly into the atmosphere.
While commonly associated with vehicle emissions, CO is also emitted by various industrial processes, residential heating, and even wildfires.
Once in the atmosphere, carbon monoxide does not need to undergo any chemical reactions to become a pollutant, qualifying it as a primary pollutant.

Exposure to high levels of CO can be harmful to human health. It can interfere with the blood's ability to transport oxygen throughout the body, potentially leading to symptoms like headaches, dizziness, and in severe cases, even death.
Because of these risks, efforts to control CO emissions have included technological advancements in engine fuel efficiency and emissions regulations aimed at reducing the CO released, especially in urban and industrial areas.

Atmospheric Pollution

Atmospheric pollution is the presence of harmful substances in the air, resulting from both human activities and natural processes. These pollutants can have significant impacts on human health, the environment, and the climate.

• Human Activities: Major sources include industrial emissions, vehicular exhaust, and agricultural practices that release pollutants like CO, nitrogen oxides (NOx), and particulate matter.
• Natural Processes: Events such as volcanic eruptions and dust storms also contribute to atmospheric pollution by releasing large quantities of particulates and gases.

The consequences of atmospheric pollution range from respiratory diseases and cardiovascular problems in humans to acid rain and global warming.
Efforts to combat pollution focus on reducing emissions, advancing clean technology, and enforcing environmental regulations. International agreements and local policies aim to monitor and limit pollutants, creating cleaner air and promoting public health.

Pollutant Classification

Pollutants in the atmosphere are classified into two main categories: primary and secondary pollutants. Understanding this classification is essential for the analysis and management of air quality.

• Primary Pollutants: These are substances emitted directly into the atmosphere in the form they exist. Examples include carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen oxides (NOx).
• Secondary Pollutants: These pollutants are not emitted directly. Instead, they form in the atmosphere through chemical reactions involving primary pollutants, sunlight, and other atmospheric components. Examples include ozone (O3) and sulfuric acid (H2SO4).

Identifying whether a pollutant is primary or secondary helps in tracing its source and understanding its impact. It also influences the strategies developed to manage, monitor, and mitigate air quality issues.
Effective pollution control strategies require distinguishing between these pollutant types and addressing them through appropriate regulations and technological interventions.