Given the data presented below for total SO₂ emission reductions in the United States, calculate the total percentage reduction and the annual percentage reduction of SO₂ emissions.

23.5 million metric tons − 10.3 million metric tons = 13.2 million metric tons total reduction

Divide the reduction by the original amount and multiply by 100 to obtain a percent reduction:

13.2 million metric tons ÷ 23.5 million metric tons × 100 = 56%

The total reduction was 56 percent.

To calculate the reduction per year, divide 56 percent by the number of years from beginning to end:

2008 − 1982 = 26 years

56% ÷ 26 years = 2.2%⁄ year

Your Turn In the United States, nitrogen oxide emissions decreased from 22.6 million metric tons (25 million U.S. tons) in 1990 to 17.2 million metric tons (19 million U.S. tons) in 2005. Calculate the total percentage reduction and the annual percentage reduction for nitrogen oxides.