Question: Types of fog and smog — formation mechanisms, causes, and environmental significance
Introduction
Fog and smog are atmospheric phenomena with distinct formation processes and pollution implications. Their accurate classification is critical for urban air-quality governance, public health policy, and climate-sensitive infrastructure planning.
Body
1. Radiation Fog: Formation and Conditions
Radiation fog develops on clear, calm nights when the Earth's surface loses heat rapidly through longwave radiation, cooling the overlying air to its dew point. Calm wind conditions are essential — strong winds would mix the air and prevent cooling. This type is common in inland valleys and plains during winter months.
2. Advection Fog: Mechanism
Advection fog forms when warm, moist air moves horizontally over a cooler surface, losing heat from below until it reaches saturation. It is prevalent along coastal regions and over cold ocean currents. Unlike radiation fog, it can persist even during daytime and under moderate winds.
3. Smog: Industrial and Anthropogenic Origins
Classical smog is a mixture of smoke and fog, historically associated with coal combustion in industrial cities — not exclusively natural forest fires. Attributing smog solely to natural causes is a misconception that obscures the dominant role of anthropogenic emissions in urban air degradation.
4. Photochemical Smog: Secondary Pollutant Formation
Photochemical smog results from the reaction of vehicular and industrial nitrogen oxides and volatile organic compounds with ultraviolet sunlight, producing ground-level ozone, peroxyacetyl nitrates, and particulate matter. It is a major public health concern in high-traffic urban centres and worsens under temperature inversions.
Conclusion
Distinguishing fog types and smog origins is not merely academic — it directly informs emission standards, urban planning, and early-warning systems. Effective air-quality governance requires precise attribution of causes rather than conflation of natural and anthropogenic processes.
Word count: 250
PYQ 2025
Consider the following statements:
Statement I: The amount of dust particles in the atmosphere is more in subtropical and temperate areas than in equatorial and polar regions.
Statement II: Subtropical and temperate areas have less dry winds.
Which one of the following is correct in respect of the above statements?
PYQ
Consider the following statements regarding the composition of the atmosphere:
Statement I: Nitrogen constitutes about 78% of the atmosphere by volume and plays an active role in combustion.
Statement II: Oxygen, though present in smaller proportion than nitrogen, is the most essential gas for sustaining life and combustion processes.
Which one of the following is correct in respect of the above statements?
PYQ
Consider the following statements about the ozone layer:
Statement I: The ozone layer is located in the stratosphere at approximately 15–35 km altitude and absorbs most of the Sun's ultraviolet-B (UV-B) radiation.
Statement II: Chlorofluorocarbons (CFCs) deplete ozone by releasing chlorine atoms that catalytically destroy ozone molecules.
Which one of the following is correct in respect of the above statements?
PYQ
Consider the following statements about the jet stream:
Statement I: Jet streams are fast-flowing, narrow air currents found in the upper troposphere and lower stratosphere.
Statement II: The subtropical jet stream flows at higher latitudes (around 50°–60°) compared to the polar jet stream which flows around 25°–30° latitude.
Which one of the following is correct in respect of the above statements?
PYQ
Consider the following statements about the Intertropical Convergence Zone (ITCZ):
1. The ITCZ is a region of low pressure formed by the convergence of northeast and southeast trade winds near the equator.
2. The ITCZ migrates northward in the Northern Hemisphere summer and southward in the Southern Hemisphere summer, following the thermal equator.
3. The ITCZ is associated with clear skies and dry conditions because of the descending air.
Which of the statements given above is/are correct?