Complete Chemistry notes on Carbon and its Environmental Chemistry for BPSC and Other Competitive Exams in 2025
General Science- 13 (Chemistry)
Here’s a detailed explanation of Carbon and its Environmental Chemistry, focusing on Pollution, Greenhouse Gases, and Ozone, along with objective questions integrated into the notes for your practice.
Carbon and its Environmental Chemistry
Environmental chemistry deals with the study of the origin, transport, reactions, effects, and fates of chemical species in the environment. Carbon, being the backbone of all organic life and a major component of fossil fuels, plays a central and critical role in various environmental issues.
1. Environmental Pollution and Carbon’s Role
Pollution refers to the introduction of contaminants into the natural environment that cause adverse change. Many major pollutants are carbon-based or directly linked to carbon activities.
A. Air Pollution:
Air pollution primarily involves gases and particulate matter released into the atmosphere.
- Carbon Monoxide (CO):
- Source: Incomplete combustion of carbon-based fuels (e.g., in vehicle engines, furnaces with insufficient oxygen).
- Effect: A highly toxic gas. When inhaled, it binds to hemoglobin in blood more readily than oxygen, forming carboxyhemoglobin, which reduces the oxygen-carrying capacity of blood, leading to suffocation and even death. It’s a “silent killer” because it’s colorless and odorless.
- Carbon Dioxide (CO2):
- Source: Complete combustion of fossil fuels (coal, oil, natural gas), deforestation (reducing CO2 absorption by trees), volcanic eruptions.
- Effect: While naturally present and essential for photosynthesis, excessive accumulation in the atmosphere acts as a major greenhouse gas, contributing to global warming.
- Particulate Matter (PM):
- Source: Incomplete combustion of fuels (e.g., diesel vehicles, industrial smokestacks), burning of biomass, dust, construction activities. Includes soot (black carbon).
- Effect: Fine particles can penetrate deep into the lungs, causing respiratory diseases (asthma, bronchitis), heart problems, and premature death. They also reduce visibility (smog) and can affect climate.
- Volatile Organic Compounds (VOCs):
- Source: Evaporation from paints, solvents, fuels, industrial processes, natural sources (plants). Many are carbon-based.
- Effect: Contribute to the formation of ground-level ozone and photochemical smog, can be toxic, and some are carcinogens.
- Other Carbon-related Air Pollutants: Methane (CH4), Chlorofluorocarbons (CFCs), Hydrofluorocarbons (HFCs) – these are also significant greenhouse gases and/or ozone-depleting substances.
B. Water Pollution (Carbon-related aspects)
- Organic Pollutants: Many industrial wastes, pesticides, herbicides, and components of sewage contain complex carbon compounds.
- Effect: They can be toxic to aquatic life, deplete dissolved oxygen (leading to death of aquatic organisms as decomposers use up oxygen to break down organic matter – measured by BOD: Biological Oxygen Demand), and cause eutrophication when nutrient-rich organic matter is introduced.
- Oil Spills: Release of crude oil or refined petroleum products into marine environments, causing widespread damage to ecosystems and wildlife.
C. Soil Pollution (Carbon-related aspects)
- Pesticides and Herbicides: Many of these agricultural chemicals are synthetic organic compounds (carbon-based) designed to target pests but can persist in soil, accumulate in the food chain, and harm non-target organisms.
- Industrial Waste: Discharge of industrial effluents containing organic chemicals (e.g., solvents, dyes) can contaminate soil.
2. Greenhouse Gases (GHGs) and Global Warming
A. Greenhouse Effect
- A natural process by which certain gases in the Earth’s atmosphere trap heat, preventing it from escaping back into space. This natural greenhouse effect keeps the Earth warm enough to sustain life.
- The gases that absorb and emit infrared radiation (heat) are called greenhouse gases (GHGs).
B. Global Warming (Enhanced Greenhouse Effect)
- Refers to the long-term heating of Earth’s climate system observed since the pre-industrial period (between 1850 and 1900) due to human activities, primarily fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth’s atmosphere.
- Key Carbon-containing Greenhouse Gases:
- Carbon Dioxide (CO2):
- Contribution: It is the most significant anthropogenic (human-caused) GHG. Although its global warming potential (GWP) per molecule is lower than some other GHGs, its sheer volume of emission makes it the largest contributor to global warming.
- Sources: Burning of fossil fuels (coal, oil, natural gas) for energy, industrial processes, transportation, deforestation.
- Methane (CH4)
- Contribution: Much higher GWP than CO2 over a shorter period (about 25 times more potent over 100 years), though it has a shorter atmospheric lifetime.
- Sources: Livestock farming (enteric fermentation), anaerobic decomposition in landfills, rice paddies, natural gas leaks, coal mining.
- Chlorofluorocarbons (CFCs) & Hydrofluorocarbons (HFCs)
- Contribution: Synthetic chemicals, extremely potent GHGs (thousands of times more potent than CO2). CFCs also cause ozone depletion.
- Sources: Refrigerants, aerosols, propellants, solvents (many older uses of CFCs are phased out).
- Carbon Dioxide (CO2):
- Impacts of Global Warming:
- Rising global temperatures.
- Melting of glaciers and polar ice caps, leading to sea-level rise.
- More frequent and intense extreme weather events (heatwaves, droughts, floods, storms).
- Changes in agricultural patterns and food security.
- Disruption of ecosystems and loss of biodiversity.
- Ocean acidification (due to increased CO2 absorption by oceans).
- Mitigation Strategies
- Reducing reliance on fossil fuels: Shifting to renewable energy sources (solar, wind, hydro, geothermal).
- Improving energy efficiency in homes, industries, and transport.
- Afforestation (planting trees) and reforestation (replanting deforested areas) to increase CO2 absorption.
- Developing carbon capture and storage technologies.
- Promoting sustainable agriculture practices.
3. Ozone (O3)
Ozone is a gas composed of three oxygen atoms (O3). It exists in two main layers of the atmosphere with very different roles.
A. Stratospheric Ozone (The “Good” Ozone):
- Location: Found in the stratosphere (10-50 km above Earth’s surface).
- Role: Forms the ozone layer, which acts as Earth’s natural sunscreen. It absorbs most of the harmful ultraviolet (UV) radiation from the sun, preventing it from reaching the Earth’s surface.
- Importance: UV radiation can cause skin cancer, cataracts, suppress the immune system in humans, and damage plant life and aquatic ecosystems.
- Ozone Layer Depletion:
- Cause: Primarily caused by man-made chemicals, especially Chlorofluorocarbons (CFCs) and halons (bromine-containing compounds), which were widely used as refrigerants, aerosol propellants, and fire suppressants. These chemicals, when they reach the stratosphere, release chlorine and bromine atoms upon exposure to UV radiation. These atoms then act as catalysts to break down ozone molecules.
- Example reaction (simplified): Cl+O3→ClO+O2 ; ClO+O→Cl+O2 (A single chlorine atom can destroy thousands of ozone molecules).
- Effects: Increased UV radiation reaching Earth, leading to higher rates of skin cancer, cataracts, weakened immune systems, damage to crops and marine plankton.
- Cause: Primarily caused by man-made chemicals, especially Chlorofluorocarbons (CFCs) and halons (bromine-containing compounds), which were widely used as refrigerants, aerosol propellants, and fire suppressants. These chemicals, when they reach the stratosphere, release chlorine and bromine atoms upon exposure to UV radiation. These atoms then act as catalysts to break down ozone molecules.
- Montreal Protocol (1987): An international treaty designed to phase out the production of numerous substances responsible for ozone depletion. It has been highly successful in reducing the emissions of ozone-depleting substances (ODS), leading to a gradual recovery of the ozone layer.
B. Tropospheric Ozone (The “Bad” Ozone / Ground-level Ozone):
- Location: Formed in the troposphere (the lowest layer of the atmosphere, near ground level).
- Formation: It is a secondary pollutant, not emitted directly but formed when sunlight reacts with nitrogen oxides (NOx) and Volatile Organic Compounds (VOCs) – both of which are primarily emitted from vehicle exhaust and industrial processes.
- Role: A key component of photochemical smog, which is a hazy air pollution mix.
- Effects: Harmful to human health (causes respiratory problems like asthma, lung damage), damages plants (reduces crop yields), and degrades materials. It also acts as a greenhouse gas.
Practice Questions
- Which gas is known as a “silent killer” due to its ability to bind with hemoglobin and reduce oxygen transport in the blood?
- A) Carbon dioxide (CO2)
- B) Carbon monoxide (CO)
- C) Methane (CH4)
- D) Sulfur dioxide (SO2)
- Rationale: Carbon monoxide (CO) is highly toxic because it forms carboxyhemoglobin, impairing oxygen delivery.
- Fine carbon particles released from the incomplete combustion of fuels are known as:
- A) Greenhouse gases
- B) Particulate matter
- C) Volatile organic compounds
- D) Acid rain precursors
- Rationale: Particulate matter, including soot or black carbon, consists of fine solid particles from incomplete combustion.
- The depletion of dissolved oxygen in water bodies due to the decomposition of organic pollutants is measured by:
- A) Chemical Oxygen Demand (COD)
- B) pH
- C) Turbidity
- D) Biological Oxygen Demand (BOD)
- Rationale: BOD measures the amount of oxygen consumed by microorganisms in decomposing organic matter.
- Which of the following greenhouse gases is considered the most significant contributor to anthropogenic global warming due to its large volume of emissions?
- A) Methane (CH4)
- B) Nitrous Oxide (N2O)
- C) Carbon dioxide (CO2)
- D) Chlorofluorocarbons (CFCs)
- Rationale: While other GHGs are potent, the sheer quantity of CO2 released by human activities makes it the largest contributor.
- A major source of methane (CH4), a potent greenhouse gas, is:
- A) Industrial combustion
- B) Volcanic activity
- C) Ocean acidification
- D) Livestock farming and landfills
- Rationale: Methane is largely produced by anaerobic decomposition, common in livestock digestion and waste decomposition in landfills.
- The melting of glaciers and polar ice caps is a direct consequence of:
- A) Ozone layer depletion
- B) Acid rain
- C) Global warming
- D) Formation of smog
Rationale: Rising global temperatures due to global warming directly cause the melting of ice bodies.
- The ozone layer, which protects Earth from harmful UV radiation, is primarily located in which atmospheric layer?
- A) Troposphere
- B) Stratosphere
- C) Mesosphere
- D) Thermosphere
- Rationale: The protective ozone layer is found in the stratosphere.
- Which class of chemicals was primarily responsible for the depletion of the stratospheric ozone layer?
- A) Carbon dioxide (CO2)
- B) Methane (CH4)
- C) Chlorofluorocarbons (CFCs)
- D) Sulfur dioxide (SO2)
- Rationale: CFCs were widely used and found to be potent ozone-depleting substances.
- Ground-level ozone, a component of photochemical smog, is considered a pollutant because it:
- A) Causes global warming directly as the main GHG.
- B) Causes respiratory problems and damages plants.
- C) Depletes the protective ozone layer.
- D) Leads to acid rain.
- Rationale: Tropospheric ozone is harmful to living organisms and is a respiratory irritant.
- The international agreement designed to phase out substances that deplete the ozone layer is known as the:
- A) Kyoto Protocol
- B) Paris Agreement
- C) Montreal Protocol
- D) Rio Summit
- Rationale: The Montreal Protocol specifically targets ozone-depleting substances.
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