Module 12 — The Atmosphere and the Role of Science in Its Sustainability

• Changes in the atmosphere cause climate changes that have long-term effects on our lives and our planet.
• In recent years a continuous rise in global temperatures — global warming — has been observed, and air pollution is considered the main cause.
• Scientists warn that if air quality continues to deteriorate at the same rate, future living organisms might need to live in closed environments (like bubbles) to protect themselves from pollution and radiation.
• Understanding what the atmosphere is made of and what it does helps us understand why it must be protected: if the proportions of its gases change, it becomes less effective in regulating temperature and in shielding Earth from harmful solar radiation.
• Understanding these changes and developing practical solutions is essential to ensure the sustainability of life for future generations.

The lesson has four parts:

1. Global warming and climate change: the greenhouse effect, its negative effects and strategies for reducing it.
2. Air pollution: carbon monoxide, sulfur and nitrogen oxides, acid rain and their effects.
3. Science and technology for protection and recovery: scrubbers, clean energy.
4. Monitoring and forecasting: satellites, weather stations, climate models and the value of forecasting.

Global warming is the continuous rise in the temperature of the air adjacent to the Earth's surface.

• It results mainly from the burning of fossil fuels (coal, oil, natural gas), which emits greenhouse gases that act like a blanket around the Earth, trapping heat in the atmosphere and raising its temperature.
• Climate change is the broader long-term change in climate patterns (temperature, rainfall, storms) that results.

The greenhouse gases that cause global warming (as listed in the book): carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), chlorofluorocarbon compounds (CFCs) and water vapour.

(The book's multiple-choice exercise treats ozone as not belonging to this list; ground-level ozone is also a weak greenhouse gas, but the book's list is the one to use in answers.)

The increase in the proportion of greenhouse gases in the atmosphere works in a manner similar to a glass greenhouse:

1. The atmosphere allows the short-wavelength solar radiation (visible light and some UV and near-infrared) to pass toward the Earth.
2. The Earth's surface absorbs this radiation and warms up.
3. The warm surface re-emits the energy as long-wavelength thermal (infrared) radiation.
4. The greenhouse gases absorb much of this infrared radiation and send part of it back toward the surface (instead of letting it escape into space). So the lower atmosphere and the surface become warmer.
5. As the concentration of greenhouse gases increases, more heat is trapped, so the Earth's surface temperature rises gradually year after year.

(In a glass greenhouse, the glass lets sunlight in but traps the warm air and reflects infrared; the atmosphere acts mainly by absorbing and re-emitting infrared.)

The natural greenhouse effect is necessary for life.

• Without any greenhouse gases the Earth's average surface temperature would be about −18 °C; the natural greenhouse effect warms it by about 33 °C to the present average of about +15 °C.
• The problem is the enhanced greenhouse effect caused by human emissions.

Problem. Estimate the Earth's average temperature if it had no greenhouse gases. Sunlight reaching the top of the atmosphere is 1361 W/m²; Earth reflects 30 % of it; the Earth intercepts sunlight over a circle (πR²) but radiates from the whole sphere (4πR²). Use σ = 5.67 × 10⁻⁸ W/m²·K⁴.

Solution. Average absorbed power per m² of surface = 1361 × 0.70 / 4 = 238 W/m². At balance, σT⁴ = 238 → T⁴ = 238/(5.67 × 10⁻⁸) = 4.20 × 10⁹ → T = 254.5 K ≈ −18.6 °C. The actual average is about +15 °C (288 K), so the greenhouse gases warm the Earth by about 33 °C.

• Problem. The concentration of CO₂ was about 280 ppm before the industrial revolution and about 420 ppm today.
• Find the percentage increase and the extra amount in 1 m³ of air.

Solution. Increase = 140 ppm; percentage = 140/280 × 100 = 50 %. In 1 m³ (1000 L) of air: 140 × 10⁻⁶ × 1000 L = 0.14 L more CO₂ than before. The global average temperature has risen by about 1.1–1.2 °C since the late 19th century.

• 1.
• Melting of ice. A large amount of fresh water is frozen in glaciers and the polar ice masses.
• As the Earth's temperature rises, ice blocks break off and melt.
• Together with the thermal expansion of the warming oceans, this causes sea-level rise and the threat of coastal flooding (a serious danger for low-lying areas such as the Nile Delta, where salt-water intrusion also damages farmland and groundwater), and creates an environmental disaster, including:

• A. Extinction of polar species because of the destruction of their natural habitat (polar bears lose sea ice for hunting; penguins and seals lose breeding grounds), which reduces biodiversity and disturbs the ecological balance.
• B. Severe climate changes: hurricanes, floods, droughts and others. A warmer atmosphere holds more water vapour and has more energy, so extreme weather events become stronger and more frequent; heat waves, wildfires and desertification increase.

Other effects (consistent with the book and your earlier lessons): coral bleaching and loss of reefs (warmer sea water — Module 3 — and acidification — Module 7); changes in rainfall that affect agriculture and water supply (Module 1); shifts in the ranges of animals and plants; spread of diseases; lower dissolved oxygen in warmer water (Module 7); and risks to human health from heat.

• Problem. If 1000 km³ of land ice melts and flows into the oceans (ocean area 3.6 × 10⁸ km²), what is the rise in sea level?
• (Ice density 917 kg/m³, water density 1000 kg/m³.)

Solution. Volume of water = 1000 km³ × 0.917 = 917 km³. Rise = volume/area = 917/3.6 × 10⁸ = 2.55 × 10⁻⁶ km = 2.5 mm. The melting of the whole Greenland ice sheet (about 2.9 million km³ of ice) would raise the sea level by roughly 7 m. (Floating sea ice, such as in the Arctic Ocean, does not raise sea level when it melts, since it already displaces its weight of water, but it reduces the reflectivity of the Arctic and so accelerates warming.)

1. Use public transportation to reduce vehicle exhaust. Vehicles emit large amounts of greenhouse gases (and other pollutants that deplete the ozone layer or form smog), so the use of private vehicles should be minimised as much as possible. Walking, cycling, shared transport, electric vehicles and metro systems help.
2. Improve energy efficiency using energy-efficient technologies in homes and factories (high-efficiency electrical appliances, LED lamps), and switch to clean, renewable energy sources such as solar energy, wind energy and hydropower. Egypt has large solar and wind potential (for example the Benban solar park near Aswan, and wind farms in the Gulf of Suez and Zafarana).
3. Increase green spaces (afforestation). Vegetation increases the amount of photosynthesis that plants perform, which has a fundamental role in absorbing carbon dioxide, the main cause of global warming; so afforestation is one of the most important methods to reduce global warming. (Trees also cool the air by transpiration and shade and reduce dust.)

Further measures: reducing food and material waste; capturing methane from landfills; sustainable agriculture; recycling; carbon capture and storage; international agreements such as the 2015 Paris Agreement (limit the global temperature rise to well below 2 °C and develop renewable energy).

Problem. (a) A car burns 1 litre of petrol (assume pure octane C₈H₁₈, density 0.74 kg/L, M = 114). How much CO₂ is produced? (b) A household replaces five 60 W incandescent lamps by five 9 W LED lamps, each used 5 hours per day. How much electricity and CO₂ is saved in a year if generating 1 kWh emits 0.5 kg CO₂? (c) A tree absorbs about 22 kg CO₂ per year. How many trees are needed to absorb the CO₂ from (a) per 1000 litres?

Solution. (a) 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O. Mass = 0.74 kg = 740 g → 6.49 mol octane → 8 × 6.49 = 51.9 mol CO₂ → 51.9 × 44 = 2285 g ≈ 2.3 kg CO₂ per litre. (b) Power saved = 5 × (60 − 9) = 255 W = 0.255 kW; energy per day = 0.255 × 5 = 1.275 kWh; per year = 1.275 × 365 = 465 kWh; CO₂ saved = 465 × 0.5 = 233 kg. (c) 1000 litres produce 2285 kg of CO₂; one tree absorbs 22 kg per year → 2285/22 = 104 trees for one year (or 104 trees needed to absorb the CO₂ of 1000 litres of petrol every year).

• Air pollution is one of the greatest dangers to the atmosphere and to the health of living organisms.
• The most prominent pollutants are: sulfur oxides (SO₂, SO₃), carbon monoxide (CO) and nitrogen oxides (NO, NO₂).

• A colourless, odourless gas (so people cannot detect it — "silent killer"), commonly produced by the incomplete combustion of fossil fuels (petrol, coal, natural gas) when there is not enough oxygen: 2C + O₂ → 2CO, 2CH₄ + 3O₂ → 2CO + 4H₂O (compared with complete combustion CH₄ + 2O₂ → CO₂ + 2H₂O). Sources: car exhaust, faulty gas heaters and water heaters (closed bathrooms), generators, burning of waste, cigarettes.
• Its small molecule penetrates rapidly from the lungs to the blood, where it competes with oxygen (O₂) to bind with the haemoglobin in the red blood cells. CO binds to haemoglobin about 200 to 250 times more strongly than oxygen, forming carboxyhaemoglobin (HbCO), a fairly stable compound that prevents the oxygen from binding to haemoglobin.
• The reduced oxygen supply to tissues causes hypoxia (cells do not get enough oxygen for cellular respiration). The cells shift to anaerobic respiration, producing and accumulating lactic acid, which causes fatigue and headache.
• With higher HbCO concentration in the blood the symptoms become serious: dizziness, loss of consciousness, brain damage and death.

First aid: move the person into fresh air immediately, call for emergency medical care, give oxygen.

Problem. The affinity of haemoglobin for CO is 220 times that for O₂. Assume that the ratio HbCO/HbO₂ at equilibrium = 220 × (partial pressure of CO / partial pressure of O₂). Estimate the percentage of haemoglobin bound to CO when the air contains 100 ppm CO (0.01 %) and 21 % O₂ (use fractions in place of partial pressures).

Solution. Ratio = 220 × (0.0001/0.21) = 220 × 4.76 × 10⁻⁴ = 0.105. Fraction HbCO = 0.105/(1 + 0.105) = 9.5 %. So even 100 ppm of CO (only 0.01 % of the air) can disable about a tenth of the blood's oxygen-carrying capacity; at 1000 ppm the ratio becomes 1.05 and HbCO is about half, which causes unconsciousness. (This is a simplified model — it ignores the gradual approach to equilibrium — but it explains the extreme danger of CO.)

• Sulfur oxides (SOₓ), especially sulfur dioxide (SO₂): emitted mainly from the combustion of coal and oil in power plants and factories (coal and heavy fuel oil contain sulfur) and from industrial processes such as oil refining and metal smelting (metal sulfide ores such as zinc blende: 2ZnS + 3O₂ → 2ZnO + 2SO₂). Volcanoes are a natural source.
• Nitrogen oxides (NOₓ), including nitric oxide (NO) and nitrogen dioxide (NO₂): produced in large quantities during high-temperature combustion — in car engines, power stations and industrial furnaces — when nitrogen and oxygen of the air combine (N₂ + O₂ → 2NO at about 1500 °C or in lightning; 2NO + O₂ → 2NO₂ afterwards). Natural source: lightning.

In the atmosphere a series of reactions makes rain acidic. (Normal rain is already slightly acidic, pH ≈ 5.6, because of dissolved CO₂; acid rain has pH below 5.6, commonly 4–4.5.)

A. Formation of sulfuric acid

1. • Sulfur dioxide, emitted from burning sulfur-containing fossil fuels, reacts with oxygen to give sulfur trioxide (the reaction occurs in the presence of catalysts, e.g.
   • sunlight/dust particles, or via other oxidants):

   2SO₂(g) + O₂(g) → 2SO₃(g)

2. Sulfur trioxide reacts with water droplets in clouds to form sulfuric acid, a very strong acid:

   SO₃(g) + H₂O(l) → H₂SO₄(aq)

B. Formation of nitric acid

Nitrogen oxides (NOₓ), formed naturally by lightning or by combustion at high temperature, react with water:

2NO₂(g) + H₂O(l) → HNO₂(aq) + HNO₃(aq) (nitrous acid + nitric acid)

and, with additional oxygen, the overall reaction is:

4NO₂(g) + O₂(g) + 2H₂O(l) → 4HNO₃(aq)

Check balances: (i) 2SO₂ + O₂ → 2SO₃: S 2 = 2; O 4 + 2 = 6 = 6 ✔. (ii) SO₃ + H₂O → H₂SO₄: S 1; O 3 + 1 = 4; H 2 ✔. (iii) 2NO₂ + H₂O → HNO₂ + HNO₃: N 2 = 2; O 4 + 1 = 5 = 2 + 3; H 2 = 2 ✔. (iv) 4NO₂ + O₂ + 2H₂O → 4HNO₃: N 4; O 8 + 2 + 2 = 12 = 4 × 3; H 4 = 4 ✔.

Problem. A coal power plant emits 6.4 tonnes of SO₂ per hour (S = 32, O = 16, H = 1). If all of it ended up as sulfuric acid, what mass of H₂SO₄ is formed per hour? How much limestone (CaCO₃) would this acid destroy?

Solution. SO₂ → SO₃ → H₂SO₄: 1 mol SO₂ (64 g) gives 1 mol H₂SO₄ (98 g). 6.4 t × 98/64 = 9.8 tonnes of H₂SO₄ per hour. H₂SO₄ + CaCO₃ → CaSO₄ + CO₂ + H₂O (1 : 1 mole ratio): 98 g acid destroys 100 g limestone, so 9.8 t of acid destroys 10 tonnes of limestone per hour. This shows how a single plant can damage large amounts of stone, soil and buildings.

A. On human health

• Direct inhalation of NO₂ and SO₃/SO₂ (and acid aerosols) irritates the respiratory tract and increases the likelihood of asthma attacks, bronchitis and pneumonia.
• Ground-level ozone (O₃) is formed secondarily from the reaction of nitrogen oxides and volatile organic compounds in the presence of sunlight (Module 10). It harms the lungs and reduces respiratory capacity.
• Fine particles formed from SO₂ and NOₓ (sulfates, nitrates) penetrate deep into the lungs and bloodstream and cause heart and lung diseases.

B. On plants

• Direct damage to leaves. Gases such as SO₂ and NO₂ enter through the stomata, causing oxidation reactions that directly damage leaf tissue and deform the stomata.
• Reduced photosynthesis. Damaged chlorophyll and clogged stomata decrease the absorption of CO₂ and so reduce the production of glucose.
• Nutrient depletion. Acid rain leaches essential salts (such as calcium and magnesium) from the soil, lowering its fertility, and releases toxic aluminium ions, so plants lack the essential elements for growth.
• (Also acid rain acidifies lakes and rivers, killing fish eggs and sensitive species.)

C. On buildings and infrastructure

• Acids react with limestone (CaCO₃) and marble, causing corrosion that damages monuments and historic buildings:

  H₂SO₄ + CaCO₃ → CaSO₄ + CO₂ + H₂O

  (Check: Ca 1; S 1; C 1; O 4 + 3 = 7 = 4 + 2 + 1; H 2 = 2 ✔.) The calcium sulfate formed is slightly soluble and flakes off, so stone surfaces crumble. Metals (iron, bronze statues) also corrode faster; Egypt's limestone monuments are especially vulnerable.

Why does this threaten the sustainability of ecosystems and of humans? Biological productivity (forests, water bodies, wild plants) declines, affecting food and resources; there is a loss of biodiversity from the death of sensitive species or the disruption of their functions; the quality of air and water falls; and societies bear health and economic burdens (health care, building repairs, loss of resources).

• Gas scrubbers installed in the chimneys of factories and power plants remove sulfur and nitrogen oxides before they are released. For example, in wet limestone scrubbers the flue gas is sprayed with a slurry of limestone/lime: SO₂ + CaCO₃ + ½O₂ → CaSO₄ + CO₂ (producing gypsum, which is used in construction), while SO₂ + Ca(OH)₂ → CaSO₃ + H₂O. Over 90 % of the SO₂ can be removed.
• Catalytic converters in car exhausts convert harmful gases: 2CO + O₂ → 2CO₂; 2NO + 2CO → N₂ + 2CO₂; and unburnt hydrocarbons to CO₂ and H₂O.
• Cleaner energy sources such as solar, wind and hydropower, which do not produce these harmful oxides; also cleaner fuels (natural gas instead of coal, low-sulfur fuels) and energy efficiency.
• Alternative technologies: electric vehicles, public transport, capture of methane, carbon capture.

The role of science goes beyond understanding the components of the atmosphere and the challenges it faces; it includes accurate monitoring of weather and climate change using advanced tools, which helps in developing preventive solutions.

(1) Satellites and remote sensing.

• Satellites perform many tasks to monitor the atmosphere.
• Remote-sensing instruments on board measure the concentrations of gases such as carbon dioxide and methane (the main global-warming gases), continuously monitor the state of the ozone layer — detecting any depletion and tracking its recovery — and give data on cloud movement and wind patterns, helping scientists understand how weather and climate patterns are changing.
• They also track sea-surface temperature, ice cover, forest loss and fires, dust storms and pollution plumes.

(2) Meteorological monitoring stations.

• Weather stations distributed around the world measure temperature, air pressure, humidity, wind speed and pollutant concentrations (Module 11).
• They help in the early detection of air pollution or dangerous weather (dust storms, heat waves).
• Historic example: in 1985 a monitoring station in Antarctica, run by the British Meteorological Office, discovered a large hole in the ozone layer.
• This discovery led to the Montreal Protocol in 1987, an international agreement that limited the use of ozone-depleting substances such as CFCs, and the ozone layer began to recover (Module 10).

(3) Climate models.

• Climate models are computer programs based on physical, chemical and biological equations describing the movements and interactions of the atmosphere.
• They allow prediction of the long-term effects of human activities, such as the effect of burning fossil fuels on the accumulation of CO₂, and the effect of deforestation on the carbon cycle and the balance of gases.
• Data collected by satellites and stations are fed in; models simulate the Earth's climate system with present and future inputs (such as emission levels) and predict possible changes, such as:

• rising temperatures;
• changes in rainfall patterns;
• increased frequency of extreme weather conditions.

• Scientists used models to predict that continued increase in atmospheric CO₂ would raise the average Earth temperature by about 1.5 to 2 °C over the coming decades.
• Enrichment (the 2015 Paris Agreement): aims to limit the rise in global temperature to less than 2 °C and urges countries to develop renewable energy (solar, wind) and reduce reliance on fossil fuels.

(4) The biological importance of forecasting

• Public health: predicting pollution levels or increases in UV radiation helps protect people from respiratory disease and skin cancer (UV index alerts, air-quality warnings).
• Agriculture: forecasting temperature and rainfall lets farmers choose the right planting and harvesting times, irrigation schedules, and protect crops from frost, heat or floods.
• Ecosystems: predicting changes helps protect sensitive organisms and plan conservation.

• Problem. A forecast says that for the next week the temperature will be 5 °C above normal and humidity 80 %.
• A farmer, a hospital and a conservation centre each receive the forecast.
• State a sensible action for each.

• Solution. Farmer: irrigate in the early morning/evening to reduce evaporation, check for fungal diseases favoured by humidity, delay planting of heat-sensitive crops.
• Hospital: prepare for heat stress cases among the elderly and children; advise people to drink water and avoid the midday sun (high humidity prevents sweat from cooling the body — Module 11).
• Conservation centre: monitor water bodies for low oxygen (warm water holds less — Module 7) and for coral/fish stress, and protect nesting birds.

Objective. Apply scientific knowledge to design a practical solution to an atmosphere-related environmental problem such as air pollution.

Tools. Recycled materials, small models, design software.

• Steps and example. (1) Choose a problem (for instance exhaust smoke or dust from a factory).
• (2) Design a model — for example a mini gas scrubber: a transparent bottle in which smoke (from a burning incense stick) is passed through a tube into a bottle containing limewater or water with a few drops of universal indicator, to show that acidic gases dissolve and the indicator turns red.
• Or a model of a green roof/afforestation plot, a low-cost air-quality sensor, or a solar-powered ventilator.
• (3) Present the model, explain scientifically how it works (which gases it removes, which reactions occur) and what its potential impact and limitations are.

Objective. Understand real applications of techniques to reduce air pollution and mitigate climate change.

• Steps. Select a case (for example the recovery of the ozone layer after the Montreal Protocol, smog control in a big city, the acid-rain programme in Europe and North America that cut SO₂ emissions by installing scrubbers, or the Great Barrier Reef bleaching forecast).
• Read the study, extract the key points (problem, causes, actions, results, costs), then discuss in a group how the solutions were applied and how they could be improved or applied in Egypt (for example, controlling the autumn "black cloud" of agricultural-waste burning; improving brick kilns; renewable energy).

• Visit a meteorological station or an environmental research centre to see how atmospheric changes are measured: instruments (thermometer screens, barometer, hygrometer, anemometer, rain gauge, radiosonde balloons, pollution analysers), data logging, and how forecasts are issued.
• Prepare questions beforehand and write a short report.

• Technology: how modern technologies (sensors, satellites, scrubbers, catalytic converters, renewable energy, smart grids, electric vehicles) reduce air pollution and improve quality of life.
• Environmental science: how to assess the environmental impact of human activities on the atmosphere (measure pollutant concentrations, compare with standards, estimate emissions) and propose sustainable solutions.

• Mixing up the greenhouse effect (heat trapping, warming) with ozone depletion (more UV). They are different problems, although both involve human emissions.
• Saying that greenhouse gases prevent the sunlight from entering. They allow short-wave radiation in and trap the long-wave infrared leaving.
• Forgetting that CO is toxic because it binds to haemoglobin much more strongly than O₂ (not because it is acidic).
• Writing 2NO₂ + H₂O → 2HNO₃ (unbalanced). The correct reactions are given above.
• Believing that acid rain is caused by CO₂ only. The strong acids come from SOₓ and NOₓ.