Air and Water Quality

Overview

Air and Water Quality is a core environmental science topic for WB TET Paper II, bridging chemistry, biology and environmental awareness. Questions typically test your knowledge of atmospheric composition, types and sources of pollution, water treatment basics and conservation strategies. This topic connects directly to the broader Environmental Studies and Science pedagogy themes in the syllabus.

For the exam, you must know the exact percentage composition of atmospheric gases, distinguish between primary and secondary pollutants, understand the water cycle and its disruption by human activity, and recall specific conservation measures. Expect 2–4 questions combining factual recall with application-based scenarios about pollution control or purification methods.

Mastering this topic also prepares you for pedagogy questions on teaching environmental concepts through experiments, field visits and real-life examples—a key NCF emphasis for upper-primary science.

Key Concepts

• **Composition of air**: Air is a mixture of gases—nitrogen (78%), oxygen (21%), argon (0.93%), carbon dioxide (0.04%) and traces of water vapour, neon, helium and ozone.

• **Air pollution defined**: Introduction of harmful substances (particulates, gases, biological molecules) into the atmosphere that cause disease, damage to living organisms or climate change.

• **Primary vs secondary pollutants**: Primary pollutants are emitted directly (CO, SO₂, NOₓ, particulate matter). Secondary pollutants form by reactions in air (ozone at ground level, PAN—peroxyacetyl nitrate).

• **Water distribution on Earth**: About 97% is saline (oceans); only 3% is freshwater, of which nearly 69% is locked in glaciers and ice caps, 30% is groundwater and less than 1% is surface freshwater.

• **Water pollution defined**: Contamination of water bodies (rivers, lakes, groundwater, oceans) by substances that make water harmful for humans, animals, plants or ecosystems.

• **Potable water criteria**: Safe drinking water must be colourless, odourless, free from pathogens and harmful chemicals, with acceptable pH (6.5–8.5) and dissolved solids (< 500 mg/L TDS recommended).

• **Water cycle disruption**: Deforestation, urbanisation and pollution alter evaporation, infiltration and runoff patterns, reducing groundwater recharge and freshwater availability.

• **Conservation principle**: Reduce consumption, reuse where possible, recycle wastewater and protect natural water bodies and air sheds from contamination.

Formulas / Key Facts

| Fact | Detail | |------|--------| | Nitrogen in air | 78.09% by volume | | Oxygen in air | 20.95% by volume | | Carbon dioxide | 0.04% (≈ 420 ppm currently) | | Safe drinking water pH | 6.5 – 8.5 | | BOD (Biochemical Oxygen Demand) | Measures organic pollution; higher BOD = more polluted water | | SPM & PM₂.₅ / PM₁₀ | Suspended Particulate Matter; PM₂.₅ particles < 2.5 micrometres cause respiratory issues | | Ozone layer location | Stratosphere (15–35 km altitude) | | Ground-level ozone | Secondary pollutant; harmful to lungs and crops | | CFC full form | Chlorofluorocarbons—deplete stratospheric ozone | | Rainwater harvesting | Captures runoff for recharge or direct use |