Q.Expand

Air pollution is any human- or naturally-caused alteration in the composition of the earth's atmosphere, which normally acts as a thermal insulator by selectively absorbing incoming UV radiation. Its major sources are grouped as transport (cars, buses, planes, trains), stationary (power plants, refineries, factories), area (agricultural burning) and natural (volcanoes, wildfires, lightning), and its main pollutants include particulate matter (PM2.5/PM10), sulphur dioxide, nitrogen oxides, and carbon monoxide -- the last especially dangerous because haemoglobin binds it more readily than oxygen, causing headache and blurred vision at low doses and coma or death at high doses. Effects include respiratory irritation, aggravated asthma/emphysema, weakened immunity and raised cardiovascular disease risk, tracked via the Air Quality Index (AQI, bands from 'Good' 0-50 to 'Hazardous' 301+) and apps like Sameer. Distinct named phenomena arising from air pollution include photochemical smog (sunlight + NOx + VOCs -> ground-level ozone and PAN, a secondary eye-irritant pollutant), global warming (via greenhouse-gas build-up), ozone depletion (via CFCs), and acid rain (via SO2/NOx) -- …