PURPOSE:  To measure the pH of acid precipitation in winter and describe the possible sources of this pollution.

MATERIALS: Field -- suitable winter clothing, tongue depressor or spoon, plastic bags with closures and masking tape labels, snow shovel, pencil. Lab -- pH meter, pH color comparators, or narrow-range pH paper; newspaper weather maps.

INTRODUCTION:  Acid precipitation has become a matter of increasing concern and debate.  In some areas, the average pH of rain and snow is as low as 4.2. The source of this acid is sulfur oxide and nitrogen oxide emissions from power plants, factories, and automobiles.  These oxides combine with the water vapor in clouds to make sulfuric and nitric acids.

Scientific studies have shown that acid precipitation, whether it is in the form of rain or snow, may damage living things in lakes, rivers and the soil.  Significant quantities of acid can accumulate in snow banks on land and frozen lakes.  Spring thaws may result in "acid shock", causing great harm to delicate ecosystems.

In this investigation, you will determine the pH of snow in various places, such as in open areas or under trees.  You will also determine the pH in the snow layers left by different snowstorms.

PREDICTION:

1.  Do you think the pH value of snow in your area will vary from place to place? Consider snow on a metal car roof, on the grass or on a tennis court. Explain your ideas.

2. Do you think the pH value of snow will vary in the different storm layers in the snowpack?  Explain your ideas.

SNOW SITE PROCEDURE:

A. As a class, make a list of possible snow collection sites, such as snow on tree branches, under a tree or on an asphalt driveway.  Divide up the sites among the class.

B.  Go to your site and collect two surface snow samples about 1 m apart from the top of the snowpack using a spoon or tongue depressor.  Keep the duplicate samples separate by placing them in different, labeled plastic bags. 

C. When you return to the lab, let the snow melt.  Determine the pH of the melted snow.  Record your data on the data sheet.  Share your data with the class.

SNOW LAYER PROCEDURE: 

D. Select an undisturbed site which is covered by 20 cm or more snow, accumulated from several storms. Dig a hole in the snow large enough to work in.

E.  Use a snow shovel to slice straight down, removing the snow to the ground.  Leave a straight, vertical wall of snow.  You may see distinct layers representing different snowstorms.

F.  IF SNOW LAYERS ARE DISTINCT:  Starting with the bottom layer, carefully scoop out a snow sample from each layer using the spoon or tongue depressor.  Keep these samples separate by placing them in different, labeled plastic bags.

IF SNOW LAYERS ARE NOT DISTINCT: Take snow samples from bottom, middle and top of the snowpack, using the spoon or tongue depressor.  Keep these samples separate by placing them in different, labeled plastic bags.

G. When you return to the lab, let the snow melt.  Determine the pH of the snow in each layer.  Record your data on the data sheet.

H.  Using weather maps, try to match the snow layers with data on snowstorms.  Try to pinpoint the origin of the snow in each layer.  Share your data with the class.

CONCLUSIONS:

3. Which site had the highest average pH value?  Which site had the lowest average pH value?  Give one possible reason for your results.

4. Did the duplicate surface snow samples from any one site differ in pH value?  Give one possible reason for your results.

5. Which snow layer was the most acidic?  Where did this storm originate?

DISCUSSION:

6. Where does the acid pollution in your area come from?  Are there local sources of acid pollution in your area?

7. Why is spring an especially vulnerable season for plants and animals in areas with acid precipitation? Consider the life cycle of aquatic organisms in your answer.

8. Do you expect the summer rain in your area to be more or less acidic than snow in winter?

ACID SNOW DATA SHEET

SNOW SITE DATA:

SNOW LAYER DATA: