Notes on Environmental Chemistry (MDC)

 Environmental Chemistry (MDC) Notes

Notes on MDC Environmental Chemistry

Unit - I

Introduction to the Environment

The environment refers to the natural world that surrounds us, including air, water, land, plants, animals, and all living and non-living things. It provides us with essential resources like oxygen, food, water, and raw materials, making life on Earth possible. The environment also includes human-made surroundings that impact our quality of life, such as cities, infrastructure, and technology.

Today, the environment faces serious challenges like pollution, deforestation, climate change, loss of biodiversity, and global warming. These problems are mainly caused by human activities such as industrialization, overuse of natural resources, and improper waste disposal.

Protecting the environment is essential for the well-being of all life forms. It requires awareness, education, sustainable practices, and cooperation at local, national, and global levels. By living in harmony with nature and making eco-friendly choices, we can ensure a healthier planet for future generations.

Composition of the Atmosphere

The Earth’s atmosphere is a layer of gases that surrounds the planet and is essential for life. It protects us from harmful solar radiation, regulates temperature, and allows us to breathe.

The atmosphere is made up of a mixture of gases, which can be classified into major components, variable gases, and trace gases.

1. Major Components (by volume in dry air):

Gas	Percentage (%)
Nitrogen (N₂)	78.08%
Oxygen (O₂)	20.95%
Argon (Ar)	0.93%
Carbon dioxide (CO₂)	0.04%
Others (inert gases, Hydrogen, etc.)	0.01%

2. Variable Gases:

These gases vary in concentration depending on location, season, and weather:

• Water vapor (H₂O) – 0 to 4% (main greenhouse gas)
• Ozone (O₃) – found mostly in the stratosphere; protects from UV rays
• Carbon dioxide (CO₂) – important for photosynthesis and the greenhouse effect
• Methane (CH₄) – a potent greenhouse gas

3. Particulates and Aerosols:

The atmosphere also contains dust, pollen, soot, smoke, and salt particles, which affect weather, climate, and air quality.

Vertical Temperature Distribution in the Atmosphere

The vertical temperature distribution refers to how temperature changes with altitude (height) in the Earth's atmosphere. The atmosphere is divided into different layers, and in each layer, temperature behaves differently due to various physical and chemical processes.

Here is a breakdown of the temperature variations in each atmospheric layer:

1. Troposphere (0–12 km)

• Temperature decreases with altitude.
• Rate: About 6.5°C per 1,000 meters (called the lapse rate).
• This is the lowest layer, where all weather phenomena occur.
• Reason: The Earth's surface heats the air above it, so the farther you go from the surface, the cooler it gets.

2. Stratosphere (12–50 km)

• Temperature increases with altitude.
• Reason: Presence of the ozone layer, which absorbs the Sun’s ultraviolet (UV) radiation and warms the layer.
• Aircraft often fly in the lower stratosphere because it’s stable and free from turbulence.

3. Mesosphere (50–80 km)

• Temperature decreases with altitude.
• Coldest layer of the atmosphere, reaching temperatures as low as −90°C.
• Reason: There is little ozone or other gases to absorb solar energy.

4. Thermosphere (80–500 km and beyond)

• Temperature increases sharply with altitude.
• Can reach up to 1,500°C or more.
• Reason: Highly energetic solar radiation is absorbed by oxygen and nitrogen molecules.

5. Exosphere (above 500–1,000 km)

• Uppermost layer; merges into outer space.
• Temperature is difficult to define because gas particles are extremely sparse and rarely collide.

Heat Budget of the Earth-Atmosphere System

The Earth's heat budget refers to the balance between the incoming solar radiation and the outgoing energy from the Earth. This balance is crucial for maintaining a stable climate and temperature on our planet.

1. Incoming Solar Radiation (Insolation)

• The Sun emits energy in the form of shortwave radiation (mainly visible light and ultraviolet).
• The total incoming solar radiation at the top of the atmosphere is about 100% (or 340 W/m² on average).

2. Distribution of Incoming Solar Energy

Here’s how the 100% of solar energy is distributed:

Energy Component	% of Total
Reflected by clouds and atmosphere	25%
Reflected by Earth's surface	5%
Absorbed by the atmosphere	20%
Absorbed by the Earth's surface	50%

Total absorbed = 20% (atmosphere) + 50% (surface) = 70%
Total reflected (lost to space) = 25% + 5% = 30%
(This 30% is called planetary albedo.)

3. Outgoing Energy (Terrestrial Radiation)

The Earth re-emits the absorbed energy in the form of longwave (infrared) radiation:

• Some of this energy escapes directly into space.
• Some is absorbed by greenhouse gases (like CO₂, CH₄, water vapor) and then re-radiated back to Earth — this is known as the greenhouse effect.

4. Balance of the Heat Budget

In the long term:

• Incoming solar radiation = Outgoing terrestrial radiation
• This maintains the Earth’s average temperature at around 15°C.
• If more energy is absorbed than emitted, the Earth warms (global warming).
• If more is emitted than absorbed, the Earth cools (global cooling).

Vertical Stability of the Atmosphere

Vertical stability refers to the atmosphere's tendency to resist or allow vertical motion (i.e., upward or downward movement of air parcels). This concept is crucial in understanding weather phenomena, such as cloud formation, thunderstorms, and turbulence.

Key Concepts

• When a parcel of air rises, it expands and cools due to lower pressure at higher altitudes.
• The stability of the atmosphere depends on the temperature difference between the rising air parcel and the surrounding air.

Biogeochemical Cycle of Carbon (C)

The carbon cycle is the natural process by which carbon atoms move through the Earth's biosphere, atmosphere, hydrosphere, and lithosphere. It is essential for sustaining life and maintaining Earth’s climate.

Major Components of the Carbon Cycle

1. Atmosphere (CO₂ form)

• Carbon dioxide (CO₂) is the primary form of carbon in the atmosphere.
• Enters and exits the atmosphere through various processes.

2. Photosynthesis

• Plants absorb CO₂ from the atmosphere.
• They convert it into glucose (C₆H₁₂O₆) and other organic molecules using sunlight.

6CO₂+6H₂O → C₆H₁₂O₆+6O₂

3. Respiration

• Plants, animals, and microbes break down glucose to release energy.
• CO₂ is released back into the atmosphere.

C₆H₁₂O₆+6O₂ → 6CO₂+6H₂O + energy

4. Decomposition

• Dead organisms are broken down by decomposers (bacteria & fungi).
• Carbon from bodies returns to soil and atmosphere.

5. Combustion

• Burning of fossil fuels (coal, oil, gas) or wood releases stored carbon as CO₂.
• Increases CO₂ levels in the atmosphere.

6. Ocean Uptake

• Oceans absorb atmospheric CO₂.
• Used by marine organisms or stored as carbonates in ocean sediments.

7. Sedimentation & Fossilization

• Over millions of years, carbon in dead organisms becomes fossil fuels or limestone (CaCO₃).

Human Impact on the Carbon Cycle

• Burning fossil fuels and deforestation increase atmospheric CO₂.
• Leads to global warming and climate change.

Unit – II

Soil Composition

Soil is a vital natural resource that forms the upper layer of the Earth’s crust. It supports plant growth, sustains life, and plays a key role in ecosystems. Soil is a mixture of minerals, organic matter, air, and water.

Major Components of Soil (by volume):

Component	Approximate %	Description
Mineral matter	45%	Inorganic particles: sand, silt, clay derived from rocks
Organic matter	5%	Decomposed plant and animal materials (humus)
Water	25%	Held in pores; available to plants
Air	25%	Occupies pore spaces not filled with water

Soil Nutrients: Macro and Micronutrients

Plants require various essential nutrients from the soil for their growth, development, and productivity. These nutrients are classified into two groups based on the amount required by plants:

1. Macronutrients (Required in large quantities)

Macronutrient	Function in Plants	Deficiency Symptoms
Nitrogen (N)	Leaf and stem growth; protein & chlorophyll formation	Yellowing of leaves (chlorosis)
Phosphorus (P)	Root development; energy transfer (ATP)	Purplish leaves; poor root growth
Potassium (K)	Enzyme activation; water regulation	Weak stems; leaf scorching
Calcium (Ca)	Cell wall structure; root and leaf development	Deformed leaves; poor root tips
Magnesium (Mg)	Central part of chlorophyll; enzyme function	Yellowing between leaf veins
Sulfur (S)	Protein and vitamin synthesis	Pale or yellow younger leaves

2. Micronutrients (Required in small quantities)

Micronutrient	Function in Plants	Deficiency Symptoms
Iron (Fe)	Chlorophyll synthesis; electron transport	Interveinal chlorosis in young leaves
Manganese (Mn)	Enzyme activation; photosynthesis	Yellow spots on leaves
Zinc (Zn)	Hormone production; enzyme activation	Shortened stems; small leaves
Copper (Cu)	Enzyme activity; lignin synthesis	Wilting; distorted young leaves
Boron (B)	Cell wall formation; reproductive development	Poor fruit/flower development
Molybdenum (Mo)	Nitrogen fixation and assimilation	Leaf margins curl; poor growth
Chlorine (Cl)	Osmotic and ionic balance	Wilting, chlorosis, leaf bronzing
Nickel (Ni)	Urease enzyme function	Leaf tip necrosis in legumes

Quick Comparison Table

Category	Nutrients
Macronutrients	N, P, K, Ca, Mg, S
Micronutrients	Fe, Mn, Zn, Cu, B, Mo, Cl, Ni

Unit III

Cement Industry as a Source of Industrial Pollution

The cement industry is one of the largest contributors to industrial pollution worldwide. While cement is essential for construction and infrastructure, its production process has significant environmental and health impacts due to the release of dust, greenhouse gases, and toxic substances.

Why Cement Production Causes Pollution

1. Raw Material Extraction

• Limestone, clay, and other materials are mined.
• Dust and noise pollution occur during mining and transportation.

2. Clinker Production (Main Stage)

• Limestone is heated to ~1450°C in a rotary kiln to form clinker.
• This process releases large amounts of carbon dioxide (CO₂).

CaCO₃→CaO+CO₂↑CaCO₃

3. Combustion of Fuels

• Coal, petroleum coke, or alternative fuels are burned.
• Releases CO₂, CO, SO₂ (sulfur dioxide), NOx (nitrogen oxides), and particulate matter.

Pollutants from Cement Industry

Pollutant	Source	Environmental/Health Impact
Carbon dioxide (CO₂)	Calcination & fuel combustion	Global warming, climate change
Particulate matter (PM)	Dust from raw materials & kilns	Respiratory problems, smog
Sulfur dioxide (SO₂)	Burning sulfur-rich fuels	Acid rain, lung irritation
Nitrogen oxides (NOx)	High-temperature combustion	Ground-level ozone, smog, acid rain
Heavy metals (e.g. Hg, Pb)	From raw materials or fuels	Toxic to humans, soil, and water

 

Environmental Impact

• Air pollution: Major source of dust and gaseous emissions.
• Vegetation damage: Dust settles on leaves, reducing photosynthesis.
• Acid rain: Due to SO₂ and NOx emissions.
• Climate change: Cement industry contributes about 7–8% of global CO₂ emissions.

Human Health Impact

• Chronic exposure to dust and gases causes:
• Asthma, bronchitis, and lung cancer.
• Eye and skin irritation.
• Long-term exposure to heavy metals can affect the nervous system and organs.

Pollution Control Measures

Strategy	Description
Dust collectors / filters	Baghouse filters, electrostatic precipitators
Alternative fuels	Use of biomass or waste-derived fuels
Carbon capture and storage (CCS)	Capturing CO₂ before release
Energy efficiency improvements	Modern kilns, waste heat recovery systems
Green cement technologies	Use of fly ash, slag, or low-carbon material

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