Acid rain itself doesn't have a distinctive smell. It can resemble a regular downpour, and the difference is only visible after a while, in the surrounding environment. However, acid rain can react with chemicals on the ground, such as spilled gasoline, and create scents. For example, hydrochloric acid (HCl) has a kind of acrid smell. Additionally, rain hitting the earth can throw dust and other particles from various sources into the air, which can also contribute to a smell.
The smell we associate with rain, often described as earthy or fresh, is actually called petrichor. This scent comes from a chemical released by bacteria called geosmin, which is present in soil. When rain falls, it releases the geosmin, creating the characteristic earthy smell.
Furthermore, acid rain can interact with volcanic gases, which are often acidic. Some of these gases, like hydrogen sulfide (H2S), have a distinct smell. This can contribute to a noticeable odor in areas affected by volcanic activity and acid rain.
