In this activity

One sample t-test of Acid Rain Data

In this activity, you will be performing a one sample t-test analysis on the pH levels of rain collected by the Environmental Protection Agency to measure the degree of acid rain. The data was collected at a rain collection station similar to the one pictured on the left in Shenandoah National Park. The Big Meadows station is part of the National Atmospheric Deposition Program's National Trends Network. The pH scale falls between 0 and 14 where 0-6.9 is acidic, and 7.1-14 is basic. Pure water has a pH level of 7.0 which is neutral on the scale, but rain water is slightly acidic usually around 5.6 on the scale. Acid rain is defined as having a pH level of 5.6 or lower.

Acid rain has a major effect on the environment. It damages plants in ecosystems. It makes streams and lakes acidic killing fish. Acid rain can damage surface paint on cars and deface buildings and statues. Because of these problems, it is important to document areas where acid rain occurs, and identify the sources contributing to its formation. One of the main factors causing acid rain is the burning of fossil fuels to produce power. This process contributes two of the major compounds that create acid rain: sulfur dioxide (SO₂) and nitrogen oxides (NO_x). The EPA states that 2/3 of the nation's sulfur dioxide and 1/4 of all nitrogen oxides come from electric power generation that relies on burning fossil fuels like coal. By collecting rain data, the EPA can determine the causes of acid rain in a particular area and measure the safety of the region's environment.

Using the java applet for a t-test developed by STATPOINT.COM, or the TI-83 calculator, perform a one sample t-test comparing the mean pH of the acid rain data to the acid rain standard PH of 5.6. The statistical hypotheses are:

Null Hypothesis
H_O: μ_{rainfall pH} = μ_{standard
pH (5.6)}

Alternate Hypothesis
H_A: μ_{rainfall pH} < μ_{standard pH (5.6)}

The acid rain pH data collected by the Environmental Protection Agency exists in three files types; one is in Excel format, one is in Text format and one is in the TI-83 Group file format. Note that it is not possible to do a one sample t-test using Excel.

Is there a significant difference between the mean pH of the acid rain data and the acid rain standard of 5.6? Why? Does the area where the data was collected have an acid rain problem?

Original work on this document was done by Central Virginia Governor's School students
Irene Tsuei, Adam Stanley, and Maury Hiller. (Class of '03)