Air Around Us

Air Around Us - Complete Guide for CBSE Class 6 Science

Introduction to Air

Air is an invisible yet essential mixture of gases that surrounds us everywhere on Earth. While we cannot see air with our naked eyes, we can feel its presence when it moves this moving air is called wind. Every living organism on our planet depends on air for survival, making it one of the most crucial natural resources.

Properties of Air

Air exhibits several distinctive properties that make it unique:

1. Colorless, tasteless, and odorless - Air has no distinct sensory characteristics
2. Has mass - Despite being invisible, air has weight
3. Occupies space - Air fills all available space in any container
4. Dissolves in water - Air can be found dissolved in water bodies
5. Compressible - Being gaseous, air can be compressed easily
6. Transparent - We can see through air clearly

An empty bottle that appears vacant actually contains air. When you invert a glass bottle and submerge it in water, the water doesn't enter because air occupies the space inside, demonstrating that air takes up space.

The Atmosphere: Earth's Protective Blanket

The atmosphere is the vast envelope of air surrounding Earth, extending many kilometers above the surface. This protective layer is absolutely essential for life on our planet because it provides oxygen for breathing and shields us from harmful solar radiation.

Altitude and Air Availability

As altitude increases, air becomes thinner with less oxygen available. This is why mountaineers climbing high peaks carry oxygen cylinders the reduced oxygen at high altitudes makes normal breathing difficult. Similarly, aircraft cabins are pressurized to ensure passengers have adequate oxygen during flight.

Main Components of Air and Their Percentages

Understanding air composition is fundamental to comprehending how our atmosphere works and supports life.

Detailed Composition of Air

Component	Percentage	Role and Importance
Nitrogen (N₂)	78%	Essential for protein synthesis in plants; relatively unreactive gas that dilutes oxygen
Oxygen (O₂)	21%	Crucial for respiration and combustion; supports life and burning processes
Other Gases	~1%	Includes carbon dioxide (0.03%), water vapor, argon, and trace gases
Carbon Dioxide (CO₂)	0.03%	Used by plants in photosynthesis; slightly sour-tasting, colorless gas
Water Vapor	Variable	Critical for water cycle; amount varies with temperature and location
Dust Particles	Variable	From natural and human sources; affects air quality

Understanding Each Component

Nitrogen (78%):

• Colorless, tasteless, and odourless gas
• Slightly soluble in water
• Does not support burning or respiration
• Highly unreactive under normal conditions
• Plants convert atmospheric nitrogen into proteins through nitrogen-fixing bacteria
• Essential for plant growth and development

Oxygen (21%):

• Colorless, tasteless, and odourless gas
• Slightly soluble in water
• Essential for respiration in all living organisms
• Supports combustion (burning) but doesn't burn itself
• Without oxygen, we would die within minutes
• Constantly replenished by plants through photosynthesis

Carbon Dioxide (0.03%):

• Colorless with slightly sour taste
• Moderately soluble in water
• Neither burns nor supports burning
• Consumed by green plants during photosynthesis
• Produced during respiration and combustion
• Critical for plant food production

Water Vapor (Variable):

• Invisible gaseous form of water
• Cannot be seen directly in air
• Essential for cloud formation and rainfall
• Plays crucial role in Earth's water cycle
• Amount varies with temperature and geographical location

How Air Composition Changes with Altitude

The composition and density of air undergo significant changes as we move higher in the atmosphere.

Vertical Air Distribution

Ground Level (Sea Level):

• Standard atmospheric pressure: 1 atmosphere
• Oxygen concentration: approximately 21%
• Air density: highest
• Breathing: comfortable and normal

Medium Altitudes (1,000 - 3,000 meters):

• Reduced air pressure
• Lower oxygen availability per breath
• Noticeable breathing difficulty during physical exertion
• Air density decreases by about 10-30%

High Altitudes (3,000 - 8,000 meters):

• Significantly reduced oxygen concentration
• Breathing becomes labored and difficult
• Risk of altitude sickness increases
• Mountaineers require supplemental oxygen
• Air density approximately 50-70% less than sea level

Very High Altitudes (Above 8,000 meters):

• Extremely thin air ("death zone" in mountaineering)
• Insufficient oxygen for sustained human survival
• Mandatory oxygen cylinder usage
• Air density less than 30% of sea level

Why This Happens

Gravity pulls air molecules toward Earth's surface, creating higher pressure and density at lower altitudes. As you ascend, there are fewer air molecules above you, resulting in:

• Decreased air pressure - Less weight of air pressing down
• Lower oxygen partial pressure - Fewer oxygen molecules per breath
• Reduced air density - Molecules are more spread out
• Temperature variation - Generally cooler at higher altitudes

This is why aircraft cabins are pressurized and why people living at high altitudes like the Himalayas or Andes have physiological adaptations for oxygen efficiency.

Why We Need Oxygen: The Life-Sustaining Gas

Oxygen is arguably the most critical component of air for survival of most living organisms on Earth.

Oxygen for Respiration

Human and Animal Respiration: All animals, including humans, inhale oxygen during breathing. This oxygen is transported through blood to every cell in the body where it:

• Enables cellular respiration to produce energy
• Breaks down glucose to release energy (ATP)
• Removes carbon dioxide as a waste product
• Maintains metabolic processes

Without oxygen:

• Cellular energy production stops
• Brain damage begins within 4-6 minutes
• Organs fail rapidly
• Death occurs within minutes

Plant Respiration: While plants produce oxygen during photosynthesis, they also consume oxygen for respiration, especially at night when photosynthesis doesn't occur.

Oxygen for Combustion

Oxygen is essential for burning (combustion) to occur. This process includes:

Fuel Combustion:

• Wood, coal, kerosene, petrol, diesel, and LPG all require oxygen to burn
• Continuous fresh air supply maintains burning
• Cutting off air supply extinguishes fire

Fire Safety Application: When someone's clothes catch fire, covering them with a woolen blanket cuts off oxygen supply, extinguishing the flames. This principle is used in:

• Fire blankets
• Fire extinguishers
• Controlled burning techniques

Common Combustion Examples:

• Burning candle requires continuous oxygen from surrounding air
• Covering burning coal with a vessel stops combustion by restricting oxygen
• Forest fires spread rapidly in windy conditions (increased oxygen supply)

Special Oxygen Supply Situations

Medical Use:

• Hospital patients with breathing difficulties receive supplemental oxygen
• Surgical patients under anesthesia require monitored oxygen
• COVID-19 patients with respiratory issues need oxygen therapy

High-Altitude Activities:

• Mountaineers carry oxygen cylinders for high-altitude climbing
• Aircraft maintain pressurized cabins with adequate oxygen
• High-altitude research stations have oxygen supply systems

Underwater Activities:

• Scuba divers carry compressed air or oxygen tanks
• Submarines maintain oxygen generation systems
• Underwater research facilities have life support with oxygen

Oxygen-Carbon Dioxide Balance in Nature

Nature maintains a perfect balance between oxygen consumption and production through interconnected processes.

How Oxygen is Replaced

Photosynthesis by Plants: Green plants act as Earth's oxygen factories:

• Use carbon dioxide from air
• Absorb water from soil through roots
• Capture sunlight energy using chlorophyll
• Produce glucose (food) and release oxygen
• Plants produce far more oxygen than they consume

The Balanced Equation: Plants consume CO₂ → Produce O₂ → Animals consume O₂ → Release CO₂ → Cycle continues

How Carbon Dioxide is Replaced

Sources of Atmospheric CO₂:

1. Animal Respiration - All animals exhale carbon dioxide
2. Plant Respiration - Plants also respire and release some CO₂
3. Combustion - Burning of fuels releases large amounts of CO₂
4. Decomposition - Breakdown of organic matter produces CO₂
5. Volcanic Activity - Natural geological process releasing CO₂

This natural cycle ensures both gases remain in relatively stable proportions, though human activities are increasingly disrupting this balance.

Air Availability for Different Organisms

Oxygen in Soil for Underground Life

Soil Air Spaces:

• Soil contains air-filled spaces between particles
• These spaces provide oxygen for soil-dwelling creatures
• Plant roots absorb oxygen from soil air for respiration

Earthworms and Soil Air: Earthworms normally live underground, breathing through their skin using soil air. However:

• During heavy rainfall, soil air spaces fill with water
• Oxygen becomes unavailable in waterlogged soil
• Earthworms must surface to breathe atmospheric air
• After rain stops and soil drains, they return underground

Root Respiration: Plant roots growing in soil require oxygen for:

• Energy production for nutrient absorption
• Growth and development
• Water uptake and transport
• Maintaining cellular functions

Oxygen in Water for Aquatic Life

Dissolved Air in Water: Water bodies (ponds, lakes, rivers, oceans) contain dissolved air, including oxygen. This dissolved oxygen is crucial for:

Aquatic Animals:

• Fish extract dissolved oxygen through gills
• Aquatic insects use various breathing mechanisms
• Crustaceans and mollusks breathe dissolved oxygen
• Marine mammals surface to breathe atmospheric air

Aquatic Plants:

• Submerged plants use dissolved oxygen for respiration
• They also produce oxygen through photosynthesis
• Help maintain oxygen levels in water bodies
• Support aquatic food chains

Limitations for Humans:

• The small amount of dissolved oxygen in water cannot support human breathing
• Divers must carry compressed air cylinders
• Submarine crews require oxygen generation systems
• Underwater habitats need continuous oxygen supply

What Causes Air Pollution and Its Health Effects

Air pollution occurs when harmful substances contaminate the atmosphere, making it dangerous for living organisms.

Major Causes of Air Pollution

1. Smoke from Combustion:

• Burning fossil fuels (coal, petrol, diesel, kerosene)
• Industrial emissions from factories
• Vehicle exhaust fumes
• Domestic cooking smoke
• Waste burning

Smoke contains:

• Fine carbon particles
• Toxic gases (carbon monoxide, sulfur dioxide, nitrogen oxides)
• Particulate matter (PM2.5 and PM10)
• Heavy metals and carcinogens

2. Industrial Activities:

• Factory chimneys emit pollutants
• Chemical processing releases harmful gases
• Power plants produce smoke and gases
• Manufacturing units generate airborne contaminants

Tall factory chimneys are designed to:

• Disperse pollutants higher in the atmosphere
• Reduce ground-level concentration
• Minimize immediate health impacts on nearby populations
• However, they don't eliminate pollution, just spread it

3. Vehicle Emissions:

• Cars, buses, trucks release exhaust gases
• Two-wheelers contribute to air pollution
• Construction equipment produces emissions
• Aircraft emissions at high altitudes

4. Dust Particles: Sources of atmospheric dust:

• Wind erosion and storms
• Road traffic stirring up settled dust
• Construction and demolition activities
• Agricultural practices (plowing, harvesting)
• Home dusting and cleaning

5. Other Sources:

• Agricultural burning (crop residue)
• Natural events (volcanic eruptions, forest fires)
• Pollen and biological particles
• Household chemicals and sprays

Health Effects of Air Pollution

Respiratory System Impact:

• Asthma development and worsening
• Chronic bronchitis
• Reduced lung function
• Respiratory infections
• Difficulty breathing

Cardiovascular Effects:

• Heart disease risk increases
• Stroke probability rises
• Blood pressure problems
• Irregular heartbeat

Long-term Health Consequences:

• Lung cancer from prolonged exposure
• Chronic Obstructive Pulmonary Disease (COPD)
• Premature death in severe pollution
• Reduced life expectancy

Vulnerable Groups:

• Children (developing respiratory systems)
• Elderly people (weakened immunity)
• People with existing respiratory conditions
• Pregnant women (affects fetal development)
• Outdoor workers

Protection Mechanism: Our Nose

Our nose serves as a natural air filter:

• Fine hairs trap larger dust particles
• Mucus captures smaller particles and microbes
• Warming air before it enters lungs
• Moisturizing inhaled air

This is why breathing through the nose is healthier than mouth breathing—it provides natural filtration and protection against dust and pollutants.

How Rainfall Cleans the Air and Removes Dust Particles

Rainfall acts as nature's air purification system, significantly improving air quality through several mechanisms.

The Air-Cleaning Process

1. Wet Deposition (Washout): As raindrops fall through the atmosphere:

• They capture suspended dust particles
• Collect pollutant gases dissolved in water droplets
• Pull down smoke particles
• Trap pollen and biological materials
• Bring all these contaminants to the ground

2. Below-Cloud Scavenging: This occurs when raindrops fall through polluted air:

• Larger dust particles collide with falling drops
• Smaller particles get incorporated into droplets
• Aerosols and fine particulate matter are captured
• Results in visible cleaner air after rain

3. In-Cloud Scavenging: Within rain clouds:

• Water vapor condenses on dust particles (condensation nuclei)
• Pollutants get incorporated into cloud droplets
• These form larger drops that eventually fall as rain
• Removes pollutants from upper atmosphere

Visible Effects After Rainfall

Immediate Observations:

• Clearer, fresher-smelling air
• Improved visibility and brightness
• Blue sky appears more vivid
• Reduced haze and smog
• Easier breathing for people with respiratory issues

Environmental Benefits:

• Reduced airborne particulate matter concentration
• Lower pollution index readings
• Temporarily improved air quality
• Settled dust on surfaces
• Cleaner vegetation (leaves washed)

The Water Vapor Cycle Connection

Role of Water Vapor in Air: Water vapor plays a crucial role in:

• Cloud Formation - Water vapor rises with hot air, cools at altitude, and condenses to form clouds
• Weather Patterns - Distribution of water vapor affects climate
• Temperature Regulation - Acts as a greenhouse gas, trapping heat
• Precipitation - Essential for rain, snow, hail formation

Complete Water Cycle:

1. Sun heats water bodies → Evaporation occurs
2. Water vapor rises into atmosphere
3. Cooling at altitude causes condensation
4. Clouds form from countless tiny water droplets
5. Droplets merge to form larger drops
6. Rain falls when drops become too heavy
7. Rainwater flows into water bodies
8. Cycle repeats continuously

This continuous cycle not only distributes water but also cleanses the atmosphere regularly, maintaining environmental balance.

Limitations of Rain Cleaning

While rain cleans the air effectively, it has limitations:

• Acid Rain - In highly polluted areas, rain absorbs pollutants and becomes acidic
• Temporary Effect - Air quality degrades again without reducing pollution sources
• Ground Pollution - Contaminants transferred to soil and water bodies
• Insufficient in Heavy Pollution - Cannot completely clean severely polluted air

Practical Uses of Air in Daily Life

Air serves numerous practical purposes beyond supporting life:

Essential Uses

1. Breathing and Respiration - Most fundamental use for all aerobic organisms
2. Combustion and Fire - Cooking, heating, power generation, industrial processes
3. Tire Inflation - Compressed air fills tires of bicycles, vehicles, aircraft
4. Seed and Pollen Dispersal - Wind carries seeds and pollen for plant reproduction
5. Wind Energy - Windmills and turbines generate electricity
6. Transportation - Sailing boats (yachts), gliders, parachutes, aircraft flight
7. Flying - Birds, bats, and insects use air for flight
8. Weather and Climate - Air movements create weather patterns and distribute rainfall

Formulas and Concepts

Concept	Representation	Explanation
Photosynthesis	6CO₂ + 6H₂O + Sunlight → C₆H₁₂O₆ + 6O₂	Plants use carbon dioxide and water to produce glucose and oxygen
Respiration	C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy	Organisms break down glucose using oxygen to release energy
Combustion	Fuel + O₂ → CO₂ + H₂O + Energy + Heat	Burning requires oxygen and produces carbon dioxide
Air Composition	N₂ (78%) + O₂ (21%) + Other gases (1%)	Standard atmospheric composition at sea level
Atmospheric Pressure	Pressure = Force/Area	Weight of air column creates atmospheric pressure

Conclusion

Air is an invaluable natural resource that sustains all life on Earth. Understanding its composition, properties, and importance helps us appreciate why protecting air quality is crucial. The delicate balance between oxygen and carbon dioxide maintained by plants and animals demonstrates nature's interconnectedness.

As human activities increasingly impact air quality through pollution, it becomes our responsibility to:

• Reduce emissions from vehicles and industries
• Plant more trees to increase oxygen production
• Use cleaner energy sources
• Minimize burning of fossil fuels
• Create awareness about air conservation

Remember, clean air is not just a resource it's a necessity for survival. By understanding how air works and what threatens its quality, we can make informed decisions to protect this precious envelope that makes life on Earth possible.