Which of the following is a main precursor of acid rain?

Acid rain primarily stems from the presence of sulfur dioxide in the atmosphere. When sulfur dioxide is emitted, often from burning fossil fuels such as coal or oil, it interacts with water vapor, oxygen, and other trace chemicals in the atmosphere. Through a series of complex chemical reactions, sulfur dioxide transforms into sulfuric acid, which contributes to the acidity of rainwater. This process significantly impacts environmental health, leading to ecosystem damage, soil degradation, and harm to aquatic life when these acids fall to the ground.

While nitrogen oxides can also contribute to acid rain by forming nitric acid, sulfur dioxide is considered the main precursor due to its larger role and the volume produced from industrial activities. Carbon dioxide, in contrast, is associated with climate change and does not have a direct effect on rain acidity. Ozone, while a significant pollutant, does not contribute to acid rain formation. Thus, sulfur dioxide is the key compound responsible for the initiation of the acid rain phenomenon, making it the correct choice.