The Chemistry of Smog in Big Cities

Smog is a mix of smoke and fog, but in modern cities it mostly means polluted air.
It forms when sunlight triggers reactions between nitrogen oxides (NOₓ) and volatile organic compounds (VOCs).
These pollutants often come from car exhaust, power plants, and factories.
The reactions produce ground-level ozone, a major ingredient in photochemical smog.
Smog can cause coughing, asthma attacks, and long-term lung damage.
Temperature inversions trap polluted air near the ground, making smog worse.
Tiny particles in smog scatter light, creating the brownish haze over cities.
Chemistry explains why smog is worse on hot, sunny days with little wind.
Regulations on fuel standards and emissions have reduced smog in many countries.
Smog chemistry shows how urban life, industry, and atmosphere collide in the air we breathe.