Problem 52 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following gases cause pollution when present in the exhaust fumes of vehicles? (a) water vapours (b) \(\mathrm{CO}_{2}\) (c) \(\mathrm{CO}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{6}\)

Step-by-Step Solution

Answer

The gas that causes pollution in vehicle exhaust fumes is carbon monoxide (CO).

Step 1: Identify Pollutant Gases

First, we need to identify which gases are considered pollutants. Common pollutants from vehicle exhausts include carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons. Carbon monoxide, in particular, is a toxic gas and a well-known pollutant.

Step 2: Analyze Each Given Option

Let's analyze each option: (a) Water vapours: This is not a pollutant; it is a natural part of exhaust fumes from the combustion of hydrocarbons. (b) CO2: While it is a greenhouse gas contributing to climate change, it is not classified as a pollutant in the conventional sense. (c) CO: This is a well-known pollutant that is harmful to human health, causing serious respiratory issues. (d) C2H6 (ethane): This is a hydrocarbon, and unburned hydrocarbons can contribute to air pollution.

Step 3: Conclusion on Pollutant Gases

From the options, the gas known to cause pollution is carbon monoxide (CO). While ethane is a hydrocarbon and contributes to smog, it is not as commonly highlighted as carbon monoxide in the context of primary vehicle pollutants. Therefore, the primary pollutant causing direct health concerns is CO.

Key Concepts

Carbon Monoxide Pollution

Carbon monoxide (CO) is a colorless and odorless gas produced by the incomplete combustion of fuels such as gasoline, wood, propane, and natural gas. In vehicle emissions, carbon monoxide results when hydrocarbons in fuel are not completely burned. Cars, trucks, and other vehicles are significant contributors to CO pollution, particularly in urban areas.

• **Health Effects**: When inhaled, CO can prevent oxygen from being carried in the blood, leading to headaches, dizziness, and in high concentrations, can be fatal.
• **Environmental Impact**: Although directly impacting human health, CO also contributes to the formation of ground-level ozone by reacting with hydrocarbons in the presence of sunlight.

To minimize exposure to carbon monoxide, cities enforce emission standards requiring vehicle engines to burn fuel more efficiently, reducing the release of CO into the atmosphere.

Hydrocarbons in Exhaust

Hydrocarbons (HC) are organic compounds consisting of hydrogen and carbon atoms. In the context of vehicle emissions, they primarily originate from unburned fuel. This happens due to incomplete combustion in the engine, meaning not all fuel is burnt, releasing these compounds into the exhaust.

• **Source**: Hydrocarbons can come from various sources, including evaporative emissions from the fuel tank and the exhaust itself.
• **Environmental Concern**: When released, hydrocarbons contribute to the formation of smog and ground-level ozone, which are harmful both to human health and the environment.

Modern cars are equipped with catalytic converters, which help reduce hydrocarbon emissions by converting them to less harmful compounds before they're released into the air.

Environmental Chemistry

Environmental chemistry involves the study of chemical processes occurring in the environment and their impacts on the ecosystem. Vehicle emissions play a significant role in environmental chemistry, as they introduce various chemicals into the atmosphere.

• **Key Pollutants**: Besides CO and hydrocarbons, vehicle emissions release nitrogen oxides, particulate matter, and other volatile organic compounds.
• **Chemical Reactions**: These pollutants can undergo chemical reactions in the atmosphere to form secondary pollutants like ozone and particulate matter, which can travel large distances, affecting regions far from their original source.

Understanding environmental chemistry is crucial for developing technologies and regulations that aim to reduce emissions and their subsequent impacts.

Air Pollution and Health Effects

Air pollution is a major concern for public health globally, with vehicle emissions being a significant contributor. Pollutants like carbon monoxide, hydrocarbons, and nitrogen oxides released from vehicles affect air quality.

• **Respiratory Problems**: Poor air quality can lead to respiratory issues such as asthma, bronchitis, and reduced lung function.
• **Cardiovascular Diseases**: Long-term exposure to polluted air increases the risk of heart disease and stroke.
• **Vulnerable Populations**: Children, the elderly, and individuals with pre-existing health conditions are especially prone to the adverse effects of air pollution.

Efforts to improve air quality include stricter emission regulations, advancement in fuel technology, and promoting alternative transportation methods like cycling and public transit.