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Name: Luka
Status:* student
Grade:* 6-8
Country:* USA
Date: Spring 2012


Question:
Does the acidity of rainwater increase as the water evaporates and its volume decreases? Simply put, does acid in acid rain water get left behind like salt during evaporation, then is concentrated into smaller volume? How is acid rain formed chemically? Does it bond or combine? Does it evaporate with the water or does it get left behind? No matter the answer, please explain why or why not.


Replies:
Luka,

Yes, the acidity of rain water will increase as water evaporates from the water and its volume decreases.

This is the opposite of dilution, which I guess you would call concentration.

The acidifying solvents, whether nitrate or sulfate are left behind as the water evaporates. These are the primary acidifying chemicals. Rainfall also scrubs out neutralizing agents such as soil - these tend to reduce the acidity of the rain water. Thus rain water acidity tends to be lessened when wind born soil or dust is significant. These chemicals dissolve in the rain water; they don't combine or bond to the water.

In nature the acidity of rain water is very much determined by the volume of rainfall. If a small amount of rain falls the rain water is more acidic than if a large amount falls (the latter is the result of dilution as the rain scrubs the atmosphere of acidifying chemicals).

David R. Cook Meteorologist Climate Research Section Environmental Science Division Argonne National Laboratory


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