10.1 Composition of Atmosphere
The Earth is covered with a blanket of air called the atmosphere which consists of several layers of gases. Air is essential for life – animals breathe it and plants use it for photosynthesis.
KEY NOTES: Atmospheric Composition
MAJOR CONSTITUENTS
• Nitrogen (N₂): 78% – Most abundant gas
• Oxygen (O₂): 21% – Essential for respiration
• Argon (Ar): 0.93% – Noble gas
• Carbon dioxide (CO₂): 0.04% – Greenhouse gas
MINOR CONSTITUENTS
• Noble gases: About 1% total
• Water vapor: Variable (0-4%)
• Trace gases: Neon, Helium, Krypton, Xenon
• Pollutants: Vary with location
IMPORTANT FACTS
• Composition varies slightly with place, season, time
• Nitrogen is chemically inert but essential for plants
• Oxygen supports combustion and respiration
• CO₂ concentration increasing due to human activities
Table 10.1: Atmospheric Composition by Volume
| Gas | Percentage | Importance |
|---|---|---|
| Nitrogen (N₂) | 78% | Dilutes oxygen, nitrogen cycle for plants |
| Oxygen (O₂) | 21% | Respiration, combustion |
| Argon (Ar) | 0.93% | Inert, industrial uses |
| Carbon Dioxide (CO₂) | 0.04% | Photosynthesis, greenhouse effect |
| Water Vapor (H₂O) | Variable | Weather, humidity, greenhouse effect |
Exercise Questions
1. At which time of the day do you expect humidity to be maximum?
Answer: Early morning or late night when temperatures are lower.
2. Which gas is released when carbonated drinks open?
Answer: Carbon dioxide (CO₂) – it creates the fizz in drinks.
Memory Trick:
“N₂ 78, O₂ 21, Ar 1, CO₂ 0.04”
Remember the percentages: Nitrogen dominates (78%), Oxygen vital (21%), Argon small (1%), CO₂ tiny (0.04%) but important.
10.2 Air Pollutants
Any substance (solid, liquid, or gas) in air that has adverse effects on human health and quality of life is called an air pollutant. Concentration is measured in parts per million (ppm).
KEY NOTES: Major Air Pollutants
7 MAJOR POLLUTANTS (90% of air pollution)
1. Carbon dioxide (CO₂) – Global warming
2. Carbon monoxide (CO) – Toxic, binds hemoglobin
3. Oxides of nitrogen (NOₓ) – Acid rain, smog
4. Oxides of sulphur (SOₓ) – Acid rain
5. Hydrocarbons – Smog, health issues
6. Particulates – Respiratory problems
7. Ozone (O₃) – Ground-level pollutant
SOURCES OF POLLUTANTS
• Fossil fuel combustion: Main source (coal, oil, gas)
• Industrial processes: Manufacturing, mining
• Transportation: Vehicles, airplanes
• Agriculture: Fertilizers, pesticides
• Natural sources: Volcanoes, decomposition
SMOG FORMATION
• Smoke + Fog = Smog
• Common in winter months
• Caused by industrial pollution + vehicle emissions
• Contains NOₓ, SO₂, particulates, VOCs
• Major problem in Pakistani cities
Table 10.2: Pollutants and Their Harmful Effects
| Pollutant | Harmful Effects | Main Sources |
|---|---|---|
| CO₂ | Global warming, sea level rise, extreme weather | Fossil fuels, deforestation |
| CO | Suffocation, binds hemoglobin, prevents O₂ transport | Incomplete combustion, vehicles |
| NOₓ | Lung damage, acid rain, eye irritation | Vehicles, power plants, lightning |
| SOₓ | Breathing difficulties, acid rain | Coal burning, industry |
| Particulates | Asthma, lung diseases, reduced visibility | Dust, smoke, construction |
| O₃ | Chest pain, coughing, throat irritation | Sunlight on NOₓ + VOCs |
Global Warming
CO₂, CH₄ increase → Greenhouse effect → Climate change
Health Issues
CO, NOₓ, particulates → Respiratory diseases, cancer
Acid Rain
SOₓ, NOₓ → Acidic precipitation → Environmental damage
Smog
Smoke + Fog → Reduced visibility, health problems
Environmental Protection Tips
• Pour liquid waste into sewers, not open drains or rivers
• Stop using environmentally hazardous substances
• Reduce fossil fuel consumption
• Use public transportation when possible
• Plant trees to absorb CO₂
10.3 Acid Rain
When rainwater has pH between 4.2 and 4.4, it is known as acid rain. First identified by Robert Angus Smith in 1852 (Father of Acid Rain). Acid rain looks, feels, and tastes like clean rain but causes widespread environmental damage.
KEY NOTES: Acid Rain Formation
FORMATION PROCESS
1. Burning fossil fuels releases SO₂ and NOₓ
2. SO₂ oxidizes to SO₃ in atmosphere
3. These gases react with water vapor
4. Form acid droplets (H₂SO₄, HNO₃)
5. Fall as acid rain, snow, or fog
CHEMICAL REACTIONS
Sulfur dioxide oxidation:
2SO₂ + O₂ → 2SO₃
SO₃ + H₂O → H₂SO₄ (Sulfuric acid)
Nitrogen oxides reaction:
2NO + O₂ → 2NO₂
2NO₂ + H₂O → HNO₂ + HNO₃ (Nitric acid)
TRANSPORT
• Acid droplets travel long distances by wind
• Acid rain often falls far from pollution source
• One country’s pollution can affect another
• International cooperation needed
Acid Rain Formation Diagram
KEY NOTES: Effects of Acid Rain
SOIL
• Increases soil acidity
• Washes away nutrients
• Releases toxic metals (Al, Hg)
• Reduces soil fertility
PLANTS & FORESTS
• Damages leaves, reduces growth
• Trees die, soil erosion occurs
• New plants cannot grow
• Reduces CO₂ absorption
AQUATIC LIFE
• Makes water acidic (pH ↓)
• Fish and aquatic animals die
• Many lakes become lifeless
• Food chain disrupted
BUILDINGS & MONUMENTS
• Corrodes stone, metal structures
• Damages historical monuments
• Taj Mahal, Parthenon deteriorating
• Increases maintenance costs
Exercise Questions
1. Which acids are made when SO₂ and NOₓ dissolve in rain?
Answer: Sulfuric acid (H₂SO₄) from SO₂ and Nitric acid (HNO₃) from NOₓ.
2. What happens to the soil if trees are destroyed by acid rain?
Answer: Soil erosion occurs, nutrients wash away, new plants cannot grow, and toxic metals may be released.
3. How does air pollution affect plants?
Answer: Reduces photosynthesis, damages leaves, inhibits growth, and can kill plants through soil acidification.
Environmental Protection & Solutions
Environmental chemistry helps us understand complex interactions in ecosystems and human impacts. Since the Industrial Revolution, human activities have significantly damaged Earth’s atmosphere through fossil fuel use, agriculture, and industrialization.
KEY NOTES: Environmental Problems
MAJOR ISSUES
• Fossil fuel combustion → Air pollution
• Fertilizers, pesticides → Water/soil pollution
• Deforestation → CO₂ increase, habitat loss
• Industrial waste → Toxic contamination
• Plastic pollution → Marine life threat
AGRICULTURAL IMPACT
• Excessive fertilizers → Water pollution
• Insecticides/pesticides → Harm animals/birds
• Soil degradation → Reduced fertility
• Bioaccumulation → Human health risks
URGENT NEEDS
• Control pollutant emissions
• Environmental education
• Sustainable practices
• International cooperation
• Renewable energy adoption
Industrial Pollution
Factories, power plants
Transportation
Vehicles, emissions
Agriculture
Chemicals, burning
Waste
Plastic, disposal
Marine Pollution
78% of marine mammals are at risk of choking with plastic.
Water Resources
Humans can use only 1% of all available water.
Deforestation
27,000 trees cut daily to make toilet paper.
Garbage Patch
Giant floating garbage patch in Pacific Ocean contains about 100 million tons of garbage.
Solutions & Prevention
• Use renewable energy (solar, wind)
• Improve fuel efficiency in vehicles
• Install pollution control devices (scrubbers, filters)
• Add lime to neutralize acidic soil/water
• Practice sustainable agriculture
• Reduce, Reuse, Recycle
• Plant trees and protect forests
Chapter 10 Solved Exercises
(ii) Indicate the source of sulphur which is responsible for the presence of oxides of sulphur in the atmosphere.
Show ExplanationExplanation: The main source of sulfur oxides (SOₓ) in the atmosphere is:
• Combustion of fossil fuels – especially coal and oil which contain sulfur
• Coal burning in power plants and industries releases SO₂
• Natural sources exist (volcanoes) but human activities dominate
• Other options: Vegetation decomposition releases methane, animal digestion releases methane, photochemical smog produces ozone
(iii) Concentration of which gas in the atmosphere is decreased by photosynthesis in plants?
Show ExplanationExplanation: Photosynthesis reduces atmospheric CO₂ concentration:
• Photosynthesis equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• Plants absorb CO₂ and release O₂
• This natural process helps regulate atmospheric CO₂
• Deforestation reduces this CO₂ absorption capacity
• Other gases: Oxygen increases, nitrogen unaffected, water vapor varies
(v) People of which age groups are most affected by air pollution?
Show ExplanationExplanation: Both children and elderly are most vulnerable:
• Children: Developing respiratory systems, breathe more air per body weight, more outdoor activity
• Elderly: Weaker immune systems, pre-existing health conditions, reduced lung capacity
• Both groups have higher susceptibility to respiratory diseases
• Air pollution causes asthma, bronchitis, pneumonia in children
• Elderly face increased risk of heart attacks, strokes
(vi) In which area there is a greater possibility of acid rain?
Show ExplanationExplanation: Industrial areas have highest acid rain probability:
• Industries burn large amounts of fossil fuels (coal, oil)
• Release maximum SO₂ and NOₓ emissions
• Power plants, factories, refineries concentrated in industrial areas
• Acid rain can travel far, affecting distant areas too
• Other areas: Villages have less industry, cities have mixed sources, water bodies may receive acid rain but don’t produce it
(vii) Why is smog not felt in summer?
Show ExplanationExplanation: Smog is less noticeable in summer because:
• Heat causes thermal convection – warm air rises carrying pollutants upward
• Better atmospheric dispersion in warm conditions
• Fog (essential for smog formation) is less common in summer
• However, photochemical smog (different type) can occur in summer from sunlight on pollutants
• Winter smog (classical smog) occurs when cold air traps pollutants near ground
(viii) Which gases contribute towards the formation of acid rain?
Show ExplanationExplanation: Both sulfur oxides (SOₓ) and nitrogen oxides (NOₓ) cause acid rain:
• SOₓ (mainly SO₂): Forms sulfuric acid (H₂SO₄)
• NOₓ (NO, NO₂): Forms nitric acid (HNO₃)
• These are the primary acid rain contributors
• CO₂ forms weak carbonic acid but not significant for acid rain (pH ~5.6)
• True acid rain has pH 4.2-4.4 from strong acids (H₂SO₄, HNO₃)
i. What is the main objective of environmental education?
Answer:
The main objectives of environmental education are:
1. To enlighten people (especially students) about environmental protection
2. To create awareness about conservation of natural resources
3. To promote sustainable development practices
4. To encourage responsible environmental behavior
5. To develop skills for identifying and solving environmental problems
6. To foster attitudes of concern for environmental quality
7. Both formal (schools) and non-formal education needed at national level
iv. How does acid rain affect forests?
Answer:
Acid rain affects forests in several ways:
1. Direct leaf damage: Acid burns leaves, reduces photosynthesis
2. Soil acidification: Makes soil too acidic for many trees
3. Nutrient leaching: Washes away essential nutrients (Ca, Mg, K)
4. Toxic metal release: Releases aluminum, mercury from soil
5. Root damage: Weakens root systems, reduces water uptake
6. Increased vulnerability: Stressed trees more susceptible to diseases, insects
7. Erosion: Dead trees lead to soil erosion on hills/mountains
8. Reduced growth: Slows or stops tree growth, can kill forests
v. In what way sulphur present in fossil fuels becomes dangerous?
Answer:
Sulfur in fossil fuels becomes dangerous through these steps:
1. Combustion: When fossil fuels (coal, oil) burn: S + O₂ → SO₂
2. Atmospheric oxidation: SO₂ oxidizes to SO₃: 2SO₂ + O₂ → 2SO₃
3. Acid formation: SO₃ reacts with water: SO₃ + H₂O → H₂SO₄ (sulfuric acid)
4. Acid rain: Sulfuric acid falls as acid rain
5. Harmful effects:
• Respiratory problems in humans
• Damage to plants and forests
• Acidification of lakes and rivers
• Corrosion of buildings and monuments
• Reduced agricultural productivity
i. How is the excessive use of insecticides and pesticides harmful for birds?
Answer:
Excessive insecticides and pesticides harm birds through:
1. Direct poisoning: Birds eat poisoned insects or seeds
2. Bioaccumulation: Chemicals accumulate in bird tissues over time
3. Eggshell thinning: DDT and similar chemicals cause thin eggshells that break easily
4. Reduced reproduction: Lower hatching success, fewer chicks
5. Food chain disruption: Insects (bird food) are killed
6. Habitat destruction: Chemicals contaminate nesting areas
7. Neurological damage: Affects navigation, feeding behavior
8. Population decline: Many bird species have decreased due to pesticides
9. Example: Bald eagles almost extincted due to DDT before ban
ii. Percentage of CO₂ in air is only 0.04%. Then how does it become harmful for the ecosystem?
Answer:
Despite being only 0.04% of atmosphere, CO₂ is harmful because:
1. Greenhouse effect: CO₂ traps heat, causing global warming
2. Concentration increase: From 280 ppm (pre-industrial) to 420 ppm today
3. Climate change: Leads to:
• Melting ice caps and glaciers
• Rising sea levels (threatens coastal areas)
• Extreme weather (heatwaves, storms, floods)
• Ocean warming and acidification
4. Ecosystem disruption:
• Coral bleaching (ocean acidification)
• Species migration and extinction
• Changing growing seasons
• Forest fires increase
5. Amplifying effect: Small increase has large climate impact
6. Long atmospheric life: CO₂ remains for 100-1000 years
i. Describe the harmful effects of the major pollutants present in the air.
Answer:
Harmful Effects of Major Air Pollutants:
1. CARBON DIOXIDE (CO₂):
• Global warming and climate change
• Melting polar ice, rising sea levels
• Extreme weather events (heatwaves, storms)
• Ocean acidification harming marine life
2. CARBON MONOXIDE (CO):
• Binds with hemoglobin 200x stronger than O₂
• Causes suffocation, dizziness, death
• Reduces oxygen transport in blood
• Particularly dangerous in enclosed spaces
3. OXIDES OF NITROGEN (NOₓ):
• Lung irritation and damage
• Forms acid rain (HNO₃)
• Contributes to smog formation
• Damages vegetation, reduces crop yields
4. OXIDES OF SULPHUR (SOₓ):
• Respiratory problems (asthma, bronchitis)
• Forms acid rain (H₂SO₄)
• Irritates eyes and throat
• Corrodes buildings and monuments
5. HYDROCARBONS:
• Some are carcinogenic (cause cancer)
• Forms ground-level ozone with NOₓ + sunlight
• Respiratory diseases
• Contributes to global warming
6. PARTICULATE MATTER:
• Enters lungs, causes asthma, bronchitis
• Reduces visibility (haze)
• Makes clothes and buildings dirty
• Can carry toxic chemicals into body
7. OZONE (O₃) at ground level:
• Chest pain, coughing, throat irritation
• Worsens respiratory diseases
• Damages plants, reduces crop yields
• Forms from NOₓ + VOCs + sunlight
8. SMOG (combined effect):
• Allergies, asthma, lung infections
• Reduces plant growth and photosynthesis
• Transportation hazards (reduced visibility)
• Major health issue in urban areas