Acid rain is primarily caused by atmospheric pollution due to which combination of gaseous oxides released from industrial, vehicular and power plant emissions?

Introduction / Context:
Acid rain is an important environmental issue discussed in atmospheric chemistry and environmental science. It involves rainfall with a pH significantly lower than 7 due to the presence of strong acids dissolved in raindrops. This question focuses on identifying which gaseous pollutants in the atmosphere are mainly responsible for the formation of acid rain, particularly in industrial and urban regions.

Given Data / Assumptions:

• Acid rain results from acids formed in the atmosphere and then dissolved in rainwater.
• Common air pollutants include oxides of sulphur, oxides of nitrogen, carbon dioxide, and others.
• We assume typical industrial and vehicular emission scenarios.
• The main acids in acid rain are sulphuric acid and nitric acid.

Concept / Approach:
The key concept is that sulphur dioxide (SO2), sulphur trioxide (SO3), and various nitrogen oxides (NO and NO2, collectively called NOx) are emitted from fossil fuel burning, power stations and vehicle exhausts. In the atmosphere, these oxides react with oxygen and water to form sulphuric acid (H2SO4) and nitric acid (HNO3). These strong acids dissolve in raindrops and lower the pH, producing acid rain. Oxides of carbon such as CO2 mainly cause mild acidity and contribute to acidification of oceans but are not the primary cause of strong acid rain in the classical sense.

Step-by-Step Solution:

Verification / Alternative check:
An alternative way to verify the answer is to remember specific chemical reactions. For example, in the atmosphere, SO2 can be oxidised to SO3, which then reacts with water to form H2SO4. Nitrogen dioxide can react with water to form HNO3 and nitrous acid. These reactions explain why regions with high SO2 and NOx emissions experience more severe acid rain. Environmental reports also list sulphur and nitrogen oxides as the main precursors of acid rain, confirming the choice of oxides of nitrogen and sulphur.

Why Other Options Are Wrong:

• Oxides of carbon and nitrogen: Carbon dioxide contributes some acidity but is not the major cause of strong acid rain. The key combination must explicitly include sulphur oxides too.
• Oxides of nitrogen and phosphorous: Phosphorus oxides are not generally major atmospheric pollutants causing acid rain.
• Oxides of nitrogen and methane: Methane is a greenhouse gas and contributes to climate change but is not a direct major source of strong mineral acids in rain.
• Oxides of carbon and sulphur: This combination leaves out nitrogen oxides, which are essential contributors to nitric acid in acid rain.

Common Pitfalls:
Students sometimes think that carbon dioxide alone is responsible for acid rain because it can form carbonic acid in water. However, typical acid rain associated with industrial pollution is due mainly to strong acids from sulphur and nitrogen oxides, not weak carbonic acid. Another pitfall is to focus only on one type of oxide, forgetting that both sulphur and nitrogen compounds are important. Remembering the formation of sulphuric and nitric acids helps avoid this error.

Final Answer:
Acid rain is mainly caused by atmospheric pollution due to oxides of nitrogen and sulphur.