The essential conditions for photochemical smog formation in the ambient atmosphere are _____.

Correct option is D

Photochemical smog is formed when primary pollutants such as nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) react under the influence of sunlight and high temperatures (T > 25°C). This type of smog is also referred to as "oxidant smog" and is characterized by the presence of ozone (O₃), peroxyacetyl nitrate (PAN), and other oxidants.
Key Factors for Photochemical Smog Formation: 1. Nitrogen Oxides (NOₓ): Emitted from vehicles, industries, and combustion processes. They act as precursors for ozone formation.
2. Volatile Organic Compounds (VOCs): Released from industrial solvents, paints, and vehicular emissions, VOCs react with NOₓ in sunlight to form photochemical oxidants.
3. High Temperature (> 25°C): Promotes the chemical reactions required for smog formation.
4. Sunlight: Acts as the catalyst, driving the photochemical reactions.
Incorrect Options: · (a) SO₂, water vapor, T > 25°C: These are conditions for acid rain formation, not photochemical smog.
· (b) Smoke, water vapor, T > 25°C: Smoke is a particulate matter and contributes to traditional smog, not photochemical smog.
· (c) VOC, SO₂, T > 25°C: SO₂ is not a major precursor for photochemical smog; it is relevant for acid deposition.
Information Booster: 1. Primary Pollutants in Photochemical Smog:
· NOₓ: Released from fossil fuel combustion.
· VOCs: Released from paints, solvents, and vehicle emissions.
2. Secondary Pollutants:
· Ozone (O₃): Harmful at ground level, formed by NOₓ and VOCs.
· Peroxyacetyl Nitrate (PAN): A toxic compound causing eye irritation.
3. Health and Environmental Impacts:
· Respiratory issues, eye irritation, and reduced lung function.
· Damage to crops and vegetation due to ozone exposure.
4. Geographic Occurrence:
· Photochemical smog is common in urban areas with heavy traffic and industrial emissions, particularly in sunny and warm climates.
Key Points: 1. Photochemical smog requires NOₓ, VOCs, sunlight, and high temperatures to form.
2. Ozone is a key component, harmful to human health and the environment.
3. Reducing vehicle emissions and controlling industrial VOC releases are essential for mitigation.