Energy fuels our world. We know from Chapter 5 that energy use is necessary for the functions of innovative development, economic success, and human lifestyle. But what is the cost of energy use? Why do air pollutants from energy matter? Non-renewable energy sources such as coal burning, oil, and gas emit chemical compounds into the atmosphere that are leading causes of pollution and climate change.

An example of one of the effects of non-renewable energy use is acid rain. Nitrogen oxides and sulfur oxides are pollutants from energy sources such as coal and oil. These air pollutants mix with water vapor (H2O) and oxygen in the atmosphere to create acidic compounds that fall to the ground in the form of rain. See chemical reactions below.

SO₂ + H₂O → H₂SO₃ (sulfurous acid), SO₃ + H₂O → H₂SO₄ (sulfuric acid) and NO₂ + H₂O → HNO₃ + HNO₂ (nitric and nitrous acids).

When these acidic compounds fall to the ground, they react with the environment and harm aquatic life in rivers, lakes, oceans, and ponds, damage forest nutrient content, and corrode limestone, metal, and marble infrastructure.

An example of this is the Adirondack Mountains in New York State, USA, a region that has been significantly affected by acid rain (Figure 14.1). This region supports many residents who rely on the area for their livelihood. The cause of acid rain is SO2 and NO2 from coal-burning power plants. Once reacted in the atmosphere, these chemicals fell in the form of rain with pH values as low as 4. The results of this were weakened trees due to soil acidification, wildlife deaths due to lower lake pH, and the release of aluminum from the soil, which is toxic to plant and animal life.

As a result of this example and many others across the US, the Clean Air Act Amendments of 1990 and other amendments introduced a cap-and-trade program (Acid Rain Program) for sulfur dioxide emissions. Acid rain has become less of an environmental issue due to this.

Chapter 14 will delve into the chemistry of acids and bases, including their structures and characteristics, as well as the calculation of pH and the interaction of acid and base titrations. After this chapter, you will understand how acid rain interacts with bases in the environment.