Basics of Environment and Pollution Control - CBT 2
What the domain tests
This section tests environment literacy as required for railway works: ecosystem structure and function, food chains, biodiversity and conservation, natural resources, and the causes, effects and control of air, water, soil and noise pollution, plus waste management and environmental law.
Core concepts
- Ecosystem components: producers, consumers, decomposers, and abiotic factors; energy flows one way through a food chain while nutrients cycle.
- The 10% law: only about 10% of energy passes to the next trophic level, so food chains rarely exceed four or five links.
- Air pollutants: primary (CO, SO₂, NOₓ, particulates) versus secondary (ozone, PAN, photochemical smog).
- Greenhouse gases: CO₂, CH₄, N₂O, water vapour, CFCs; CO₂ dominates by volume of emissions, methane is far more potent per molecule.
- Ozone layer depletion is caused mainly by CFCs and halons; the Montreal Protocol (1987) phases them out.
- Water quality: BOD measures oxygen demanded by microbes to break down organic matter - high BOD means heavy organic pollution. COD is a broader chemical measure.
Worked example
Explain how photochemical smog forms over a city. Vehicle exhaust releases NO and unburnt hydrocarbons in sunlight; UV radiation splits NO₂ into NO and free oxygen atoms; these atoms combine with O₂ to form ozone; ozone then reacts with hydrocarbons to give peroxyacetyl nitrate (PAN). Because every step needs sunlight, the smog peaks in the afternoon, which explains why it is called photochemical.
Traps that cost marks
Calling CO₂ an air pollutant that directly depletes ozone - it is a greenhouse gas, not an ozone-depleting substance. Confusing BOD (organic load) with COD (total chemically oxidisable matter). Forgetting that noise is measured in decibels on a logarithmic scale.