Environmental Chemistry

Chemistry plays a crucial role in both causing and solving environmental problems. As Nepal rapidly urbanizes, understanding environmental chemistry helps us make informed decisions about pollution, climate change, and sustainable development.

Air Pollution

Major air pollutants include:

• CO (carbon monoxide): From incomplete combustion of fuels. Toxic because it binds to haemoglobin more strongly than O₂.
• SO₂ and NO₂: From burning fossil fuels. Cause acid rain (H₂SO₄ and HNO₃ in rain).
• Particulate matter (PM2.5): Tiny particles that penetrate deep into lungs. Kathmandu Valley frequently has high PM2.5 levels.
• CO₂: Greenhouse gas from combustion. Major contributor to global warming.

Acid rain: SO₂ + H₂O --> H₂SO₃ (sulfurous acid); 2SO₂ + O₂ + 2H₂O --> 2H₂SO₄

The Greenhouse Effect

Greenhouse gases (CO₂, CH₄, N₂O, CFCs) trap infrared radiation from the Earth, warming the atmosphere. This is the greenhouse effect.

While a natural greenhouse effect keeps Earth warm enough for life, enhanced greenhouse effect from human activities causes global warming, leading to:

• Melting of glaciers (critical for Nepal -- Himalayan glaciers feed major rivers)
• Rising sea levels
• Extreme weather events
• Changes in rainfall patterns affecting agriculture

Ozone Depletion

The ozone layer (O₃) in the stratosphere protects Earth from harmful UV radiation.

CFCs (chlorofluorocarbons) from refrigerants and aerosols destroy ozone:

• CF₂Cl₂ --> CF₂Cl + Cl (UV light breaks the C-Cl bond)
• Cl + O₃ --> ClO + O₂ (one Cl atom can destroy thousands of O₃ molecules)

The Montreal Protocol (1987) successfully reduced CFC production worldwide.

Water Pollution

Common water pollutants:

• Industrial waste (heavy metals like Pb, Hg, Cd)
• Agricultural runoff (pesticides, fertilizers causing eutrophication)
• Sewage (pathogens, organic matter)

The Bagmati River in Kathmandu is a well-known example of water pollution that community efforts are working to clean.

Green Chemistry (Introduction)

Green chemistry aims to design chemical processes that reduce or eliminate hazardous substances. Key principles include:

• Prevention: Preventing waste is better than cleaning it up
• Atom economy: Maximize the incorporation of starting materials into the final product
• Safer solvents: Use water or non-toxic solvents when possible
• Renewable feedstocks: Use plant-based raw materials instead of petroleum

Nepal Connection

Nepal faces unique environmental challenges: glacier melting threatens water supplies, Kathmandu's air quality frequently exceeds WHO guidelines, and rivers face pollution. Understanding environmental chemistry empowers students to be part of the solution.

Key Takeaways

• Major pollutants: CO, SO₂, NO₂, PM2.5, CO₂
• Greenhouse effect: CO₂ and CH₄ trap heat, causing global warming
• CFCs deplete the ozone layer; the Montreal Protocol addresses this
• Green chemistry focuses on pollution prevention at the source