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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