Photochemical smog formation

• A. It occurs only at night
• B. NOx reacts with water to form ozone
• C. NOx and VOCs react with heat and sunlight to produce ozone
• D. It is unrelated to sunlight

Answer: (C)

Photochemical smog forms when sunlight energizes reactions between nitrogen oxides released from vehicles and industrial processes and volatile organic compounds in the air. The sun’s energy drives the photolysis of NO2, producing an oxygen atom that quickly combines with O2 to make ozone near the ground. VOCs supply reactive radicals that keep the reaction going, accelerating ozone formation. Heat makes these reactions happen faster, so sunny, hot days often have more smog. That’s why this is a daytime phenomenon tied to sunlight, and it isn’t simply NOx reacting with water. Humidity and other factors can influence amounts, but the heart of photochemical smog is the combination of NOx, VOCs, heat, and sunlight producing ozone.