Environmental Science

Choose the Correct Answer

Correct Answer : Option c

Explanation
Statement 1 is correct: When sunlight falls on stagnant air under low humid conditions in the presence of pollutants such as SO2 soot, nitrogen oxides and hydrocarbons, photochemical smog is formed (photochemical: chemical reactions in the presence of light). Smog stays close to the ground and reduces visibility and causes irritation. Photochemical smog is also called PAN smog due to the formation of peroxyacetyl nitrate or PAN and ozone which are formed from hydrocarbons and nitrogen oxides in the presence of solar radiation. PAN and ozone are called photochemical oxidants. Both of these are toxic irritants to human lungs.

Statement 2 is correct: Carbon monoxide (CO) and hydrocarbons (HC) contribute to the formation of photochemical smog by reacting with nitrogen oxides (NO2) under sunlight to produce secondary pollutants like ozone and PAN.

Statement 3 is correct: Temperature inversion occurs when air temperature increases with height instead of decreasing. This typically happens in the early evening and lasts until morning as the Earth's surface cools rapidly after sunset, while the air above remains warmer. Calm winds and clear skies enhance this effect, trapping cold air near the ground, especially in valleys. This stable atmospheric condition prevents air mixing, causing pollutants and smoke to accumulate, leading to smog formation. The inversion persists overnight but dissipates after sunrise as the ground warms, allowing normal air circulation to resume. This phenomenon impacts weather, air quality, and agriculture.