Not all rain is created equal. Imagine rain that doesn’t just water the plants, but can actually damage them. That’s the reality of acid rain.

Acid rain refers to any form of precipitation, rain, snow, sleet, or even fog, that contains elevated levels of sulfuric and nitric acids. It forms when sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) are released into the atmosphere, primarily from the burning of fossil fuels like coal, oil, and natural gas. These gases react with water vapor, oxygen, and other chemicals in the atmosphere to create acidic compounds, which then fall to the ground with precipitation.

Acid rain can have serious environmental impacts. When it reaches the ground, it can lower the pH of soil and water, making lakes and streams too acidic for many fish, insects, and aquatic plants to survive. In forests, acid rain can weaken trees by damaging leaves and bark, leaving them more vulnerable to disease, extreme weather, and pests.

It also affects human-made structures. Buildings, statues, and monuments, especially those made of limestone or marble, can slowly erode when exposed to acid rain over time. In urban areas, it can contribute to the degradation of infrastructure and increase maintenance costs.

Regulations like the Clean Air Act in the United States, emissions of SO₂ and NOₓ have been significantly reduced over the past few decades, leading to a decrease in acid rain in many regions. However, it remains a concern in areas with high industrial activity or limited pollution controls.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.