Smog
Also called: Photochemical smog, Urban smog · Topic: Geographical Issues: Pollution, Urban Waste, Slums and Land Degradation · NCERT: Class 11, Ch 10 "Water in the Atmosphere"; Class 12, Ch 9 "Geographical Perspective on Selected Issues and Problems"
Meaning
Smog is a smoky fog over cities. The word joins "smoke" and "fog". It forms when smoke and pollutants from vehicles, factories and burning mix with fog. In sunlight, gases from vehicle exhaust can also react to form photochemical smog. Smog makes it hard to see far, and it is very harmful to health. It hurts the lungs, heart and blood system.
Example
Every winter, Delhi is covered in smog. Pollution from vehicles, dust and burning gets trapped near the ground by temperature inversion. Smoke from crop fires in Punjab and Haryana adds to it.
Don't confuse with
- Fog: fog is only tiny water droplets in the air near the ground, and it is natural. Smog contains pollutants.
- Acid rain: this is rain with a pH below about 5.6, formed when sulphur and nitrogen oxides turn into acids. It falls to the ground, while smog hangs in the air.