10.1 Introduction & Atmosphere Composition
🌍 Environmental Chemistry
- Study of chemicals & pollutants in environment
- Effects on living & non-living things
- Part of environmental education
- Industrial revolution increased pollution
- Fossil fuels = major pollution source
- Fertilizers, pesticides harm ecosystems
💨 Atmosphere Composition
78.0% – Major constituent
21.0% – Major constituent
~1.0% – Minor constituents
| Minor Constituent | Percentage | Importance |
|---|---|---|
| Carbon dioxide (CO₂) | 0.04% | Greenhouse gas, photosynthesis |
| Noble gases (Ar, Ne, He, etc.) | About 1% | Inert, various industrial uses |
| Water vapor (H₂O) | Variable (0-4%) | Humidity, weather, clouds |
From Textbook Exercises:
1. When is humidity maximum? Early morning/night (cooler air holds less moisture → condensation)
2. Gas released from carbonated drinks? CO₂ (carbon dioxide under pressure)
10.2 Air Pollutants
☣️ What are Air Pollutants?
- Substances in air with adverse effects on health/life
- Can be solid, liquid, or gas
- Concentration measured in ppm (parts per million)
- 1 ppm = 1 part pollutant per million parts mixture
📋 7 Major Air Pollutants
| No. | Pollutant | Formula | Main Source |
|---|---|---|---|
| 1 | Carbon dioxide | CO₂ | Complete combustion |
| 2 | Carbon monoxide | CO | Incomplete combustion |
| 3 | Oxides of nitrogen | NOₓ (NO, NO₂) | High temp combustion |
| 4 | Oxides of sulphur | SOₓ (SO₂, SO₃) | Burning sulphur fuels |
| 5 | Hydrocarbons | CH₄, C₂H₆, etc. | Incomplete combustion |
| 6 | Particulates | Dust, smoke, pollen | Industrial processes |
| 7 | Ozone | O₃ | Photochemical smog |
🔥 Sources of Air Pollution
CO₂, CO, NOₓ, SOₓ, HC
SO₂, particulates, metals
NOₓ, CO, HC, particulates
Volcanoes, decomposition
1. Rapid population growth
2. Urbanization
3. Industrialization
4. Transportation increase
🌫️ Smog Formation
- Smoke + Fog = Smog
- Winter phenomenon (fog present)
- Causes: Industrial pollution + vehicle emissions + crop burning
- Contains: NOₓ, SO₂, particulates, VOCs
- Not felt in summer (fog absent, heat rises smoke)
10.3 Acid Rain
⚗️ What is Acid Rain?
- Rainwater with pH 4.2-4.4
- Discovered by Robert Angus Smith (1852)
- “Father of Acid Rain”
- Caused by atmospheric pollution
- Corrosive nature causes environmental damage
🔬 Formation Process
Fossil fuel burning releases SO₂ & NOₓ
SO₂ → SO₃ (oxidized by NOₓ/O₂)
Gases mix with atmospheric moisture
Form acid droplets (H₂SO₄, HNO₃)
⚠️ Effects of Acid Rain
From Textbook Exercises:
1. Acids from SO₂ and NOₓ in rain? H₂SO₄ (sulfuric acid) and HNO₃ (nitric acid)
2. Soil if trees destroyed? Soil washed away (erosion), no new plants can grow
Harmful Effects & Prevention
💀 Harmful Effects of Major Pollutants
| Pollutant | Harmful Effects |
|---|---|
| CO₂ (Carbon dioxide) | Global warming → ice melt, sea rise, extreme weather |
| CO (Carbon monoxide) | Poisonous, binds hemoglobin → suffocation/death |
| NOₓ (Nitrogen oxides) | Lung damage, eye irritation, acid rain, vegetation damage |
| SOₓ (Sulphur oxides) | Eye irritation, breathing difficulty, acid rain |
| Hydrocarbons | Pneumonia, breathing issues, global warming |
| Particulate Matter | Asthma, breathing problems, dirty clothes, reduced visibility |
| Ozone (O₃) | Chest pain, coughing, throat irritation, congestion |
1. Reduces photosynthesis (blocks sunlight)
2. Damages leaves/needles
3. Increases susceptibility to diseases
4. Reduces growth/yield
🛡️ Prevention & Solutions
Individual Actions:
• Pour liquid waste into sewers (not open drains/rivers)
• Stop using environmentally hazardous substances
• Reduce, Reuse, Recycle
• Use public transport/carpool
• Plant trees
Industrial Solutions:
• Install scrubbers in factories
• Use cleaner energy sources
• Implement waste treatment systems
• Use catalytic converters in vehicles
Exercise Questions – Complete Solutions
Multiple Choice Questions:
ii) Source of sulphur responsible for oxides of sulphur in atmosphere?
Answer: (d) Combustion of fossil fuels
Detailed Explanation: Fossil fuels (coal, petroleum) contain sulphur impurities. When burned:
S (in fuel) + O₂ → SO₂ (sulphur dioxide)
2SO₂ + O₂ → 2SO₃ (sulphur trioxide)
Other options wrong:
(a) Decomposition of vegetation → releases methane, not SOₓ
(b) Animal digestion → releases methane (CH₄)
(c) Photochemical smog → forms ozone, not SOₓ
iii) Which gas concentration decreased by photosynthesis?
Answer: (c) Carbon dioxide
Detailed Explanation: Photosynthesis equation:
• Plants absorb CO₂, release O₂
• CO₂ concentration decreases during day
• Oxygen increases
• Nitrogen unaffected (not used in photosynthesis)
• Water vapor variable but not primarily reduced by photosynthesis
v) Which age groups most affected by air pollution?
Answer: (d) Both children and aged people
Detailed Explanation: Vulnerable groups:
Children: Developing lungs/immune systems, breathe more air per kg body weight
Aged people: Weakened immune systems, pre-existing conditions (asthma, heart disease)
Also affected: Pregnant women, people with respiratory diseases
Young/middle-aged adults generally more resistant but still affected
vi) Where greater possibility of acid rain?
Answer: (c) Around industrial areas
Detailed Explanation: Acid rain requires:
1. High emissions of SOₓ and NOₓ (industrial areas)
2. Atmospheric moisture
3. Wind patterns carry pollutants
Industrial areas: High fossil fuel combustion → more SOₓ/NOₓ
Big cities: Also affected but less than heavy industrial zones
Villages/water bodies: Less industrial activity → less acid rain
Note: Acid rain can fall far from source due to wind transport
vii) Why smog not felt in summer?
Answer: (b) Because due to heat of Earth the smoke rises up
Detailed Explanation: Smog = Smoke + Fog
Summer conditions:
1. No fog (requires cool, moist conditions)
2. Heat creates convection currents → pollutants rise/disperse
3. Better air circulation
Winter conditions:
1. Fog common (cool, moist air)
2. Temperature inversion traps pollutants near ground
3. Less air movement
Other options incorrect:
(a) Fog absent but not only reason
(c) They can mix but conditions unfavorable
(d) Similar fossil fuel use in summer
x) Which gases contribute to acid rain?
Answer: (d) Both oxides of nitrogen and sulfur
Detailed Explanation:
Primary acid rain gases:
1. SOₓ (SO₂, SO₃): Forms H₂SO₄ (sulfuric acid)
2. NOₓ (NO, NO₂): Forms HNO₃ (nitric acid)
Reactions:
CO₂ excluded: Forms weak carbonic acid (H₂CO₃), pH ~5.6, not considered “acid rain”
Acid rain pH: 4.2-4.4 (requires strong acids from SOₓ/NOₓ)
Short Answer Questions:
i. What is main objective of environmental education?
Answer: To enlighten people (especially students) about importance of environmental protection and conservation.
Detailed Explanation:
Objectives:
1. Create awareness about environmental issues
2. Teach importance of conservation
3. Develop skills to address environmental problems
4. Foster attitudes of responsibility toward environment
5. Promote sustainable development practices
Forms: Formal (schools/colleges) & Non-formal (community programs)
National need: Urgent due to increasing pollution levels
iv. How does acid rain affect forests?
Answer: Damages trees through soil acidification, nutrient leaching, direct leaf damage, and increased susceptibility to diseases.
Detailed Effects:
1. Soil Acidification:
• Dissolves essential nutrients (Ca, Mg, K) → washes away
• Releases toxic metals (Al, Hg) that harm roots
2. Direct Damage:
• Burns leaves/needles (brown spots, premature falling)
• Reduces photosynthesis
3. Root Damage:
• Toxic Al³⁺ ions damage fine root hairs
• Reduces water/nutrient uptake
4. Ecosystem Disruption:
• Trees die → soil erosion on hills/mountains
• New plants cannot establish
• Whole forest ecosystems collapse
v. How does sulphur in fossil fuels become dangerous?
Answer: When burned, sulphur forms SO₂/SO₃ → acid rain → environmental damage.
Detailed Process:
Resulting Dangers:
1. Acid Rain: pH 4.2-4.4, corrosive
2. Health Effects: Breathing difficulties, eye irritation
3. Environmental Damage: Soil acidification, water pollution
4. Material Damage: Corrodes buildings, monuments
5. Visibility Reduction: Sulfate particles create haze
Prevention: Use low-sulphur fuels, install scrubbers
Constructed Response Questions:
i. How is excessive use of insecticides/pesticides harmful for birds?
Answer: Birds are harmed through direct poisoning, food chain contamination, eggshell thinning, and habitat destruction.
Detailed Harmful Effects:
1. Direct Poisoning:
• Birds eat poisoned insects/seeds
• Chemicals accumulate in body
• Can cause immediate death
2. Bioaccumulation:
• Chemicals move up food chain
• Higher predators get concentrated doses
• Example: DDT in fish → eagles
3. Eggshell Thinning:
• DDT interferes with calcium metabolism
• Eggs break during incubation
• Reduced reproduction rates
4. Habitat Destruction:
• Kills insects that birds eat
• Reduces food availability
• Can poison water sources
Famous Example: Bald eagles nearly extinct due to DDT in 1960s
ii. CO₂ is only 0.04% of air. How does it become harmful?
Answer: Despite low concentration, CO₂ is powerful greenhouse gas causing global warming through enhanced greenhouse effect.
Detailed Explanation:
1. Greenhouse Gas Properties:
• CO₂ absorbs infrared radiation (heat)
• Traps heat in atmosphere
• Natural level: 0.03% (pre-industrial)
• Current: 0.04% (25% increase)
2. Enhanced Greenhouse Effect:
• Human activities add extra CO₂
• Burning fossil fuels: ~35 billion tons/year
• Deforestation reduces CO₂ absorption
3. Harmful Effects:
• Global Warming: Average temperature increase
• Ice Melt: Polar ice caps/glaciers melting
• Sea Level Rise: Thermal expansion + meltwater
• Extreme Weather: Heatwaves, storms, floods
• Ocean Acidification: CO₂ dissolves → carbonic acid
Key Point: Small concentration change → large climate impact
Descriptive Questions:
i. Describe harmful effects of major pollutants in air.
Answer: Each pollutant has specific harmful effects on health, environment, and materials.
Detailed Description:
• Global Warming: Traps heat → climate change
• Ice Melt: Polar regions warming
• Sea Rise: Coastal flooding
• Weather Extremes: More storms, droughts
• Poisonous: Binds hemoglobin 240× stronger than O₂
• Suffocation: Red blood cells can’t carry O₂
• Headache → Death: Progressive symptoms
• Colorless, odorless → hard to detect
• Respiratory Damage: Lung irritation, asthma
• Acid Rain: Forms HNO₃
• Smog Formation: Photochemical reactions
• Plant Damage: Leaf discoloration, reduced growth
• Breathing Problems: Asthma, bronchitis
• Eye Irritation: Redness, watering
• Acid Rain: Forms H₂SO₄
• Material Damage: Corrodes metals, stone
• Respiratory Issues: Pneumonia, coughing
• Smog Formation: Reacts with NOₓ → O₃
• Global Warming: Methane potent greenhouse gas
• Carcinogenic: Some HC cause cancer
• Lung Damage: Asthma, bronchitis, cancer
• Visibility Reduction: Haze, smog
• Material Soiling: Dirty buildings, clothes
• Climate Effects: Some particles cool, some warm
• Respiratory: Chest pain, coughing, throat irritation
• Lung Function: Reduces lung capacity
• Plant Damage: Reduces crop yields
• Material Damage: Degrades rubber, textiles
Cumulative Effects: Smog worsens all effects, affects photosynthesis, reduces visibility, damages ecosystems
From Textbook Box:
Amazing Environmental Facts:
1. 78% of marine mammals at risk of choking with plastic:
• Plastic pollution in oceans estimated 150 million tons
• Animals mistake plastic for food
• Causes intestinal blockage, starvation
• Great Pacific Garbage Patch: 1.6 million km²
2. Humans can use only 1% of all available water:
• Earth’s water: 97% salty oceans, 2% frozen ice, 1% freshwater
• Of that 1%: 0.3% in rivers/lakes, 0.7% groundwater
• Much groundwater too deep/contaminated to use
3. 27,000 trees cut daily for toilet paper:
• World has ~3.04 trillion trees
• Deforestation rate: 10 million hectares/year
• Toilet paper industry major contributor
• Alternatives: Recycled paper, bamboo products