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Airborne Chemicals, Decrease Rain pH
Name: Mitch
Status: Student
Grade: 9-12
Location: MA
Country: United States
Date: September 2008
Question:
What are some chemicals pumped into the atmosphere that
decrease the pH of rain?
Replies:
Two main chemicals that contribute to acid rain are called NOx and SOx --
NOx is made of one nitrogen and one or more oxygen atoms (N O subscript x,
hence "NOx") and SOx is made of one sulfur and one or more oxygen atoms (S O
subscript x, hence "SOx"). For example, when SO3 combines with water, it
forms H2SO4, which is sulfuric acid. Sulfuric acid is a major component of
acid rain. Likewise, NOx combines with water to form HNO3, which is nitric
acid.
Hope this helps,
Burr Zimmerman
The major contributors to "acid rain", that is a lowering of the pH, are the
"acid forming gases". These include
CO2 (from the combustion of hydrocarbons), SO2 (from the combustion of sulfur
in coal) -- (which oxidizes to SO3 and reacts with water to form sulfuric acid
H2SO4), nitrogen oxides (especially NO2), and HCl. These are not necessarily
the chemicals pumped into the atmosphere directly, but can be the products of
the decomposition of other substances. So any compound containing those elements
are candidates for sources that can lower the pH of rain. Not all of the sources
are the result of human activity. Pine trees and other conifers, for example,
are "natural" sources of terpenes, a type of hydrocarbon that can oxidize in
the atmosphere to form acidic products.
Vince Calder
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Update: June 2012
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