Earth’s Atmosphere and Environmental Challenges: Composition, Pollution, and Solutions

Posted on Jan 16, 2025 in Geology

Earth’s Atmosphere: Composition and Structure

The atmosphere of Earth is composed of about 78% nitrogen, 21% oxygen, 0.04% carbon dioxide, 0.96% argon, and trace amounts of neon, helium, methane, krypton, hydrogen, as well as water vapor.

• Nitrogen: The most plentiful gas in the air, it is one of the primary nutrients critical for the survival of all living organisms.
• Oxygen: Required for the survival of life, green plants produce oxygen during photosynthesis, maintaining a constant oxygen content in the air.
• Carbon Dioxide: An important heat-trapping gas, or greenhouse gas, that comes from the extraction and burning of fossil fuels. It is the most important raw material which plants utilize during the photosynthesis process.

The vertical structure of the atmosphere consists of several layers, separated from one another by a change in the slope of the graph of temperature versus altitude.

Troposphere

1. The lowest layer of the atmosphere in which living organisms operate.
2. Extends up to 10km.
3. Region of strong air movements and cloud formation.
4. Water vapor and dust occur in extremely variable concentrations.
5. All climatic and weather changes take place in this layer.
6. Temperature ranges from 14°C to -56°C.
7. The tropopause is a zone that separates the troposphere from the stratosphere.
8. Changes in temperature with height are known as the lapse rate.
9. The decrease of temperature with increasing altitude is called the positive lapse rate.

Stratosphere

1. The region above the tropopause, about 50 km above Earth’s surface.
2. Temperature ranges from -56°C to -2°C.
3. In this zone, the temperature-altitude curve shows a warming trend with increasing altitude.
4. The increase of temperature with increasing altitude shows a negative lapse rate.
5. Heat is produced during the formation of ozone, responsible for the temperature increase.
6. Ozone acts as a protective shield for life on Earth from the injurious effects of the sun’s ultraviolet rays.
7. The region above the stratosphere is known as the stratopause.
8. Weather-related phenomena are absent; therefore, airplanes fly in the stratosphere for a smooth ride.

Mesosphere

1. Located between about 50 and 80 kilometers above Earth’s surface.
2. Known as the coolest layer of the atmosphere.
3. Temperature ranges from -2°C to -92°C.
4. The decrease of temperature with increasing altitude shows a positive lapse rate.
5. Most meteors burn up in this layer. Sounding rockets and rocket-powered aircraft can reach the mesosphere.
6. The region above the mesosphere is known as the mesopause.

Thermosphere/Ionosphere

1. Located between about 80 and 700 kilometers above Earth’s surface; its lowest part contains the ionosphere.
2. Temperature ranges from -92°C to 1200°C as it is much closer to the sun.
3. Shows a negative lapse rate as temperature increases with height.
4. Gases absorb solar radiation and undergo ionization.
5. The ionosphere is mostly used for communication purposes due to electrical conductivity.
6. The ionosphere helps in radio communication.
7. The International Space Station (ISS) orbits in the thermosphere.

Exosphere

1. Located between about 700 and 10,000 kilometers above Earth’s surface.
2. The highest layer of Earth’s atmosphere, merging with the solar wind at its top.
3. Molecules are of extremely low density, so this layer doesn’t behave like a gas, and particles escape into space.
4. There’s no weather in the exosphere.
5. Most Earth satellites orbit in this layer.

Note: The atmosphere absorbs most cosmic rays, protecting living things from their harmful effects. It also maintains Earth’s heat balance, serving as insulation from heat loss and stabilizing weather and climate.

Air Pollutants: Sources and Impacts

Carbon Monoxide: An odorless, invisible gas formed from incomplete combustion, with nearly 50% originating from automobiles. Also present in cigarette smoke, it is highly poisonous and reduces the oxygen-carrying capacity of blood.

Sulfur Dioxide: A colorless gas with a sharp, choking odor, formed during the combustion of coal or oil containing sulfur. Most emissions come from power plants. It can cause eye and throat irritation, harm lung tissue, and contribute to acid rain, damaging ecosystems and structures.

Nitrogen Dioxide: A pungent, irritating gas known to cause pulmonary edema. It contributes to acid rain and plays a role in the formation of photochemical smog. Ozone, a key component of smog, is formed by a reaction between nitrogen dioxide and hydrocarbons in sunlight, contributing to global warming.

Lead: Inhaled lead particulates are harmful, especially to children, causing learning disabilities, seizures, or death. Sources include oil refining, smelting, and other industrial activities.

Effects of Air Pollution

Human Health

• Eye irritation from pollutants like NOx, O3, smog, and particulates.
• Estimated 0.62 million mortalities in India in 2010 due to PM2.5 pollution, projected to increase.
• Hydrogen fluoride can cause fluorosis and mottling of teeth.
• Radioactive isotopes can cause anemia, leukemia, cancer, and genetic defects.
• Indoor air pollution from biomass and kerosene is linked to various health issues.

Materials

• Direct damage to structural metals, coatings, fabrics, and other materials.
• Corrosion of metals, e.g., galvanized iron.
• Soiling and deterioration of limestone and marble.
• Blackening of lead-based paints by H2S.

Vegetation

1. Reduced Photosynthesis and Growth: Particulate matter, ozone, sulfur dioxide, and nitrogen oxides hamper chlorophyll’s absorption capability.
2. Damage to Leaf Structure and Function: Necrotic spots, premature leaf drop, yellowing, and stippling disrupt essential functions.
3. Changes in Reproductive Success: Pollutants distort pollen integrity, affecting reproduction.

Strategies for Air Pollution Control

• Drive less by walking, biking, carpooling, or using public transportation.
• Use less energy and reduce consumption.
• Recycle and reuse items to reduce waste.
• Avoid plastic bags, which are harmful to the environment.
• Use fans instead of air conditioners.
• Avoid burning garbage or having backyard fires.
• Plant and care for trees.
• Use electric or hand-powered lawn equipment.
• Keep your car serviced on time.

Air Pollution Control Technologies

Gravity Settling Tank

Used to remove large, abrasive particles (>50 μm) from gas streams using gravitational and inertial forces. There are two types: expansion chambers and multiple-tray chambers.

Cyclone Separator

Consists of a cylindrical shell, conical base, dust hopper, and inlet. Centrifugal force separates solid particles from the gas. Efficiency depends on particle mass, gas velocity, and cyclone diameter.

Electrostatic Precipitator

Uses an electric field to separate liquid or solid aerosols from a gas stream. Particles are charged and drawn to a collecting surface, then removed by rapping or vibrating.

Major Air Pollution Incidents

Bhopal Gas Tragedy

On December 3, 1984, about 45 tons of methyl isocyanate escaped from an insecticide plant in Bhopal, India, killing thousands and causing long-term health issues for many survivors.

London Smog

The Great London Smog of 1952 resulted from a mix of fog and smoke from coal-burning factories and vehicles, leading to severe air pollution and significant health impacts.

Ozone Layer Depletion

Causes

Ozone depletion is primarily caused by industrial chemicals, especially halocarbon refrigerants, solvents, propellants, and blowing agents (CFCs, HCFCs, halons). These are transported to the stratosphere, where they release halogen atoms that break down ozone.

Reactions

CFCs react with the ozone layer in the presence of UV radiation, breaking it down into oxygen molecules. This was observed in the 1970s and led to the Montreal Protocol in 1973.

Antarctic Ozone Hole

An annual phenomenon from September to early December, where frigid temperatures and CFCs/HCFCs trigger ozone depletion. The Montreal Protocol, signed in 1987, aimed to phase out ozone-depleting substances.

Effects of Ozone Layer Depletion

Human Beings

• Increased risk of skin cancers, rashes, and aging.
• Breathing difficulties, chest pain, and throat irritation.
• Suppressed immune system leading to severe infectious diseases.
• Eye problems like cataracts and photokeratitis.
• DNA mutation.

Plants

• Altered physiological and developmental processes, inhibiting photosynthesis.
• Mutation.
• Altered biodiversity.
• Affected plant competitive balance, pathogens, and biogeochemical cycles.

Aquatic Ecosystem

• Affected productivity of marine/freshwater organisms.
• Affected distribution of phytoplankton.
• Damaged early development stages of fish, shrimp, crabs, amphibians, and other animals.
• Affected reproductive capacity and impaired larval development.

Bio-Geochemical Cycles

• Altered sources and sinks of greenhouse gases.
• Changes in plant matter production and decomposition.
• Reduction of primary production and plankton growth.
• Increased degradation of aquatic dissolved organic matter.

Non-Living Materials

• Accelerated photodegradation of synthetic polymers and biopolymers.
• Affected material quality, leading to discoloration and loss of mechanical integrity.

Control Measures for Ozone Layer Depletion

1. International Agreements
   • Montreal Protocol: Aims to phase out ODS.
2. Regulations and Policies
   • National Legislation: Regulate ODS use.
   • Import/Export Controls: Monitor and restrict ODS trade.
3. Alternatives and Substitutes
   • Adoption of Safer Chemicals: Encourage non-ozone-depleting substances.
4. Public Awareness and Education
   • Outreach Campaigns: Inform about ozone layer protection.
5. Research and Monitoring
   • Ongoing Research: Monitor ozone levels.
   • Satellite Monitoring: Track ozone layer changes.
6. Support for Developing Countries
   • Financial and Technical Assistance: Help comply with ozone protection measures.

Smog

Smog is a combination of smoke and fog caused by burning coal, vehicular emissions, and industrial fumes. There are two types:

Sulfurous Smog

Also called “London smog,” it results from a high concentration of sulfur oxides, particularly from coal burning. Aggravated by dampness and high particulate matter.

Photochemical Smog

Also known as “Los Angeles smog,” it occurs in urban areas with many automobiles. Nitrogen oxides and organic compounds react in sunlight to form ozone.

Effects of Smog

• Increased atmospheric pollution levels.
• Highly toxic to humans, causing sickness, shortened life, or death.
• Contains soot, ozone, CO, SO2, which are carcinogens.
• Accentuated temperature inversions and reduced precipitation.
• Smog-related haze lowers visibility.

Control Measures for Smog

• Avoid exercising outdoors; use indoor gyms or exercise machines.
• Stay away from high-traffic areas; wear Masks N95 and N99 if necessary.
• Maintain tobacco-free indoors.
• Use green plants like aloe vera and snake plants to purify indoor air.
• Stop burning wood or trash.

Water Pollution

Water pollution is the contamination of water bodies, usually due to human activities. It involves changes in the physical, chemical, or biological properties of water, harming living organisms.

Properties of Water

Water is a simple molecule with one oxygen atom bonded to two hydrogen atoms. It is a universal solvent, exists in solid, liquid, and gas forms, and has a lower density as ice than as liquid water.

Earth’s oceans contain 97% of the planet’s water; 3% is freshwater. Most freshwater is trapped in glaciers and ice sheets. Drinking water, or potable water, is safe for human and animal consumption.

Water Pollution Sources

Water can be contaminated by agricultural activities, industrial operations, landfills, animal operations, and sewage treatment processes. Point source pollution comes from a single origin, while nonpoint source pollution comes from multiple dispersed sources.

Types of Water Pollutants

Chemical Pollutants

• Organic Pollutants: Herbicides, pesticides, pharmaceuticals, fuel, industrial solvents, and synthetic hormones.
• Inorganic Pollutants: Nitrate, phosphate, heavy metals, chloride, and radioactive isotopes.

Biological Pollutants

Pathogens from human and animal fecal waste due to inadequate sewage treatment.

Physical Sources of Pollution

Trash, sediments, and thermal pollution from mining, deforestation, and agriculture.

Water Treatment and Purification Technologies

1. Preliminary Treatment: Reduce velocity, remove heavy materials and foreign objects.
2. Primary Treatment: Settle solid particles and skim fats, oil, and grease.
3. Secondary Treatment: Biological process using bacteria to metabolize organic matter.
4. Tertiary or Advanced Treatment: Remove suspended solids, BOD, plant nutrients, dissolved solids, and toxic substances.
5. Final Treatment: Disinfect to kill microorganisms using UV, ozonation, or chlorination.
6. Solids Processing: Digest solids to reduce pathogens and produce biosolids.

Treatment with Chlorine and/or Chloramine: Used by most communities for disinfection.

Ozone Disinfection: Effective against most pathogens, including protozoa.

Ultraviolet Disinfection: Chemical-free process effective against parasites like Cryptosporidium and Giardia.

Fluoridation: Adding fluoride to water to prevent tooth decay.