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 that has detrimental impacts on both the health of organisms and climate.

An example of one of the effects of non-renewable energy use is acid rain. Nitrogen oxides and sulfur oxides are pollutants emitted from the combustion of 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)

NO₂ + H₂O → HNO₃ + HNO₂ (nitric and nitrous acids).

When these acidic compounds fall to the ground, they can 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). The SO₂ and NO₂ emitted from coal-burning power plants are hydrated and come down in the form of rain with pH values as low as 4. As a conseqence, the area has seen weakened trees due to soil acidification, wildlife deaths from lower lake pH levels, and the release of aluminum from the soil, which is toxic to both plant and animal life.

To address this issue, under the US Clean Air Act Amendments of 1990, lawmakers introduced a cap-and-trade program called the Acid Rain Program for sulfur dioxide emissions. The program sets a permanent cap on tht total SO₂ emissions that can be emitted by power plants across the US. This was the first national cap and trade program in the US and introduced a system of market-based incentives to decrease SO₂ pollution. Because this pollutant is short-lived, its consequences are regionally confined and emissions can be contained through a cap and trade program. Since this program began in 1995, acid rain has become less of an environmental issue.

This chapter will further explore acid-base chemistry with an emphasis on the equilibrium aspects of this important reaction class. You will calculate pH and analyze the interaction of acids and bases . After this chapter, you will understand how acid rain interacts with bases in the environment.