Answer: photochemical oxidising smog.
- A classical reducing smog
- B acid rain droplets
- C the stratospheric ozone layer
- D photochemical oxidising smog
Correct answer: D. photochemical oxidising smog
Explanation: PAN, along with ozone and aldehydes, is formed by the action of sunlight on nitrogen oxides and hydrocarbons, and is a marker of photochemical (oxidising) smog.
Sunlight passes through the atmosphere and warms the surface; the surface re-radiates this energy as infrared heat, which greenhouse gases (CO₂, CH₄, water vapour) absorb and trap - a naturally beneficial process that intensifies into global warming as gas concentrations rise from human activity.
Concept context
Pollution, global warming, ozone depletion, deforestation, and sustainability. Important for NEET and general awareness.