1. Sulfur dioxide (SO2): This gas is released primarily from burning fossil fuels, especially coal. It reacts with water in the atmosphere to form sulfuric acid (H2SO4), which is a strong acid.

2. Nitrogen oxides (NOx): These gases are also produced by burning fossil fuels, particularly from vehicle emissions. They react with water and oxygen in the atmosphere to form nitric acid (HNO3), another strong acid.

These acids then dissolve in rainwater, making it more acidic than it would naturally be. This is the main cause of acid rain.