Conservation: Environmental Pollution and Climate Change
Pollutants
Air pollutants: sulphur dioxide, nitrogen oxides, carbon monoxide, ozone and particulates. PM2.5 is the deadliest because it reaches the alveoli; the AQI reports the worst sub-index. In water, BOD measures biodegradable organic load and COD the total oxidisable matter; high BOD means oxygen depletion and eutrophication downstream. Noise is measured in dB(A). Soil and solid waste problems include leachate and persistent plastics.
Climate change
Greenhouse gases: carbon dioxide from fossil fuel and land-use change, methane (GWP about 28), nitrous oxide (about 265) and fluorinated gases. The Keeling curve tracks the rise. The IPCC assesses; the UNFCCC is the treaty; Kyoto (1997) set Annex I targets; Paris (2015) uses NDCs to hold warming well below 2°C and pursue 1.5°C. India's NDC includes an emissions-intensity cut and a non-fossil capacity share by 2030, with net zero pledged for 2070. The National Action Plan on Climate Change (2008) has eight missions. Ozone depletion is separate - CFCs under the Montreal Protocol (1987).
Worked example
A river has dissolved oxygen 8 mg/L upstream and 3 mg/L below a sewage outfall. The 5 mg/L drop signals organic pollution; DO below 4 mg/L stresses fish. Reasoning: BOD measures oxygen consumption, not the concentration of sewage itself.
Traps
Do not equate the ozone hole with global warming. Do not name carbon dioxide as the only greenhouse gas. PM2.5 is finer, not coarser, than PM10.