Question

Which of the following are essentially required for photochemical smog formation in ambient atmosphere?

• A. Smoke, water vapour and low temperature (> 25 degrees)
• B. NO_x, SO₂ and high temperature (> 25 degrees)
• C. NO_x, VOCs and high temperature (> 25 degrees)
• D. Smoke, NO_x and low temperature (< 25 degrees)

Answer 1

The Correct Option is C

The essential requirements for photochemical smog formation in ambient atmosphere are NOx, VOCs and high temperature (>25°C).

Additional Context:

• Key components:
  • NOx (Nitrogen Oxides): From vehicle emissions and combustion processes
  • VOCs (Volatile Organic Compounds): From fuels, solvents, and industrial emissions
  • Sunlight (UV radiation): Drives photochemical reactions
  • High temperature: Accelerates reaction kinetics (>25°C ideal)
• Formation process:
  • NOx + VOCs + sunlight → Ozone (O₃) + PAN (Peroxyacyl nitrates)
  • Secondary pollutants cause eye irritation and respiratory problems
• Other options analysis:
  • Smoke + water vapor + low temp: Describes London-type smog (industrial smog)
  • NOx + SO₂: SO₂ contributes to acid rain, not photochemical smog
  • Smoke + NOx + low temp: Incomplete combination missing VOCs and sunlight
• Characteristic features:
  • Brownish haze (unlike gray industrial smog)
  • Peaks in afternoon due to sunlight intensity
  • Common in cities like Los Angeles, Mexico City
• Control measures:
  • Catalytic converters in vehicles (reduces NOx)
  • VOC emission controls in industries
  • Use of alternative fuels

Correct Answer: (3) NOx, VOCs and high temperature (>25°C).