Environmental Chemistry

Environmental Chemistry: The branch of chemistry which deals with the study of chemicals and other pollutants in the environment.

Scope: Covers adverse effects of chemicals on living and non-living things.

Atmosphere: Earth is covered with a blanket of air called atmosphere, made up of several layers of gases. Essential for life on Earth.

Composition of Atmosphere:

• Nitrogen ($N_2$): 78%
• Oxygen ($O_2$): 21%
• Argon (Ar): 0.934%
• Carbon dioxide ($CO_2$): 0.03%
• Noble gases: About 1%
• Water vapours: Variable (depends on humidity)

Air Pollutant: Any substance (solid, liquid or gas) in the air which has adverse effect on human health and quality of life.

Concentration Expression: Parts per million (ppm). 1 ppm = one part of pollutant per million parts of mixture.

Major Air Pollutants:

• Carbon dioxide ($CO_2$)
• Carbon monoxide (CO)
• Oxides of nitrogen ($NO$, $NO_2$ - collectively $NO_x$)
• Oxides of sulphur ($SO_2$, $SO_3$ - collectively $SO_x$)
• Hydrocarbons (Methane, ethane, etc.)
• Particulates (Dust, pollens, metallic compounds)
• Ozone ($O_3$)

Sources: Burning of fossil fuels, volcanic eruption, decomposition of vegetation, industrial activities, vehicle emissions, crop burning.

Carbon dioxide ($CO_2$): Higher levels lead to increased global warming, causing ice caps to melt, oceans to warm, sea levels to rise. Extreme weather changes (heat waves, heavy rains, wildfires).

Carbon monoxide (CO): Extremely poisonous gas causing suffocation and death. Stops red blood cells from carrying oxygen.

Oxides of nitrogen ($NO_x$): Damages lungs, irritates eyes, damages vegetation. Causes acid rain affecting buildings and statues made of limestone.

Oxides of sulphur ($SO_x$): Irritates eyes, causes breathing difficulties and acid rain.

Hydrocarbons: Cause pneumonia, coughing, breathing and lung diseases. Also cause global warming.

Particulate matter: Irritates eyes, causes severe breathing problems (especially asthma). Reduces visibility (produces haze). Makes clothes dirty.

Ozone ($O_3$): Causes chest pain, coughing, throat irritation and congestion.

Definition: When rain water has pH between 4.2 and 4.4, it is known as acid rain.

Formation: Burning fossil fuels releases $SO_2$ and $SO_3$ (due to sulphur in fuels). $SO_2$ converts to $SO_3$ in presence of nitrogen oxides. Nitrogen oxides produced by combustion and lightning.

Chemical Equations:

• $S + O_2 \to SO_2$
• $2SO_2 + O_2 \to 2SO_3$
• $N_2 + O_2 \to 2NO$
• $2NO + O_2 \to 2NO_2$
• $SO_2 + H_2O \to H_2SO_3$ (Sulphurous acid)
• $NO_2 + H_2O \to HNO_2$ (Nitrous acid)

Effects:

• Soil: Increases acidity, dissolves nutrients, releases toxic aluminum and mercury
• Plants: Damages vegetation, destroys tree roots, soil washed away
• Aquatic life: Makes water too acidic for animals
• Human health: Toxic substances pollute water supplies
• Agriculture: Less affected; farmers can neutralize with crushed lime (CaO)
• Structures: Damages buildings, statues, automobiles (e.g., Taj Mahal, Parthenon)

Definition: Progressive warming up of Earth's surface due to blanketing effect of man-made carbon dioxide, methane, water vapours and other gases in atmosphere.

Mechanism: Sun emits short-wave radiation that passes through greenhouse gases to heat Earth's surface. At night, hot Earth surface emits long-wave radiation that is absorbed by greenhouse gases. This prevents radiation from reaching space, reducing speed at which Earth cools, increasing temperature.

Sources of Greenhouse Gases:

• $CO_2$: Burning coal, oil, natural gas. Deforestation reduces capacity to remove $CO_2$
• Methane ($CH_4$): Increased decay of vegetation, digestion in animals, rice farming

Effects:

• Rise in sea levels: Water expansion, ice melting in Antarctic and Greenland
• Increase in rainfall: May cause worldwide floods
• Effects on agriculture: Changes in crop growth (wheat/rice better, maize/sugarcane worse)
• Hot summer and winter: Shorter, warmer winters; longer, hotter summers

Planting Trees: Photosynthesis removes air pollution by absorbing $CO_2$ and releasing $O_2$. Equation: $6CO_2 + 6H_2O \xrightarrow{\text{Chlorophyll, Sunlight}} C_6H_{12}O_6 + 6O_2$. Particulate matter deposits on leaves, branches, trunk surfaces.

Catalytic Converters: Used in automobile exhaust to reduce emissions. Three-way catalytic converter performs:

• Reduces nitrogen oxides: $2NO \to N_2 + O_2$
• Oxidizes CO: $2CO + O_2 \to 2CO_2$
• Oxidizes hydrocarbons: $C_xH_y + 2O_2 \to CO_2 + 2H_2O$

Low-Sulphur Fuels: Use fuels with less sulphur content.

Flue Gas Desulphurization: Removes $SO_2$ from exhaust gases using adsorbents like calcium oxide (removes up to 95%).

Renewable Energy: Sun, wind, water, geothermal, biomass. Solar and wind energy generate electricity without damaging environment.

Air Quality Index (AQI): A rating system showing how bad the atmosphere is. AQI under 50 = good quality (safe outdoors). AQI over 300 = hazardous.

High Risk Groups: Children under 18, adults over 65, people with chronic heart/lung disease, diabetics, outdoor workers.

Protection Measures:

• Reduce time outdoors when air quality is bad
• Wear masks (N95 masks have better filtration)
• Keep windows and doors closed; use air conditioner/air cleaner
• Install carbon monoxide detector to detect increased CO levels
• Consult doctor if symptoms appear

Effects of Polluted Air: Affects lungs, heart, brain. Air pollutants enter bloodstream, cause coughing, eye itching, poor quality of life, hospitalization, cancer, premature death.