Acid rain is caused by emissions of sulfur dioxide and nitrogen oxides from fossil fuel combustion. When these gases mix with water vapor and rain, they produce acid rain that falls to Earth. Acid rain damages trees, aquatic life in lakes and streams, buildings, and can harm human health. It harms trees by causing leaves and needles to turn brown and fall off, and damages fish by raising acid levels in lakes and killing eggs and fish. Acid rain also dissolves stonework on buildings. To mitigate acid rain, power plants can install emissions scrubbers, people can reduce electricity usage, and vehicles can install catalytic converters.