What is the main environmental concern associated with sulfur dioxide emissions?

Analysis

The question asks for the primary environmental impact caused by the release of sulfur dioxide ($SO_2$) into the atmosphere. This is a common topic in environmental chemistry, specifically regarding air pollution.

Concept Explanation

Sulfur dioxide ($SO_2$) is a gas primarily produced by the combustion of fossil fuels (like coal and oil) that contain sulfur impurities, as well as from volcanic activity and industrial processes.

When $SO_2$ is released into the atmosphere, it reacts with water vapor, oxygen, and other chemicals to form sulfuric acid ($H_2SO_4$). This process is represented by the following chemical reactions:

1. $2SO_2 + O_2 \rightarrow 2SO_3$
2. $SO_3 + H_2O \rightarrow H_2SO_4$

When this sulfuric acid dissolves in rainwater, it lowers the pH of the rain, making it acidic. This phenomenon is known as acid rain. Acid rain has harmful effects on the environment, including the acidification of lakes and streams, damage to forests, and the corrosion of buildings and statues made of limestone or marble.

Step-by-Step Evaluation

• Option A (Formation of acid rain): This is the direct and well-documented result of sulfur dioxide emissions. As explained above, $SO_2$ reacts with atmospheric moisture to form acidic precipitation.
• Option B (Global warming potential): While some gases contribute to global warming (like $CO_2$ and $CH_4$), $SO_2$ is not a primary greenhouse gas. In fact, sulfate aerosols can have a slight cooling effect on the climate.
• Option C & D (Depletion of the ozone layer): Ozone depletion is primarily caused by chlorofluorocarbons (CFCs) and other ozone-depleting substances, not by sulfur dioxide.

Conclusion

Based on the chemical properties of sulfur dioxide and its interaction with the atmosphere, the correct environmental concern is the formation of acid rain.

Exam Tip: Whenever you see "Sulfur dioxide" or "Nitrogen oxides" in an environmental chemistry question, immediately associate them with acid rain. If you see "CFCs," associate them with ozone layer depletion.