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Unformatted text preview: power plants with
ones that utilize solar energy and nuclear energy.
Methane, nitrous oxide, and CFCs are also strong absorbers of IR. These gases are present in only trace
amounts, but enhance the greenhouse effect significantly because they absorb IR at wavelengths that water and
CO2 cannot absorb. In a sense they close an open window that would allow some IR to escape the greenhouse. Acid Rain. The term "acid rain" was coined in 1872 by an English chemist who used it to describe the
increasingly acid precipitation that fell on the industrial city of Manchester. In the century since then, acid rain Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website Chemistry in the Atmosphere 3 61
has grown to be an environmental problem of global proportions. Acid rain is rainwater with a pH of less than
5.5. Precipitation in the northeastern part of the U.S. has an average pH of 4.3 and in some specific storms the
pH has been as low as 2.8.
The text points out that "normal" rain is slightly acid because it contains carbonic acid. As rain passes
through air containing carbon dioxide, the CO2 dissolves and forms carbonic acid. Carbon dioxide is an acid
CO2 (g) + H 2 O(l) → H2 CO3 (aq)
Because carbonic acid is a weak acid, the pH of rain normally will not go below 5.5. The presence of several
stronger acids accounts for the lower pH values of acid rain. Acid rain usually contains sulfuric acid (H2 SO4 )
and nitric acid (HNO3 ). We will discuss only sulfuric acid.
These acids do not start out in the atmosphere as oxoacids. The text points out that the precursors of the
oxoacids are the acidic oxides, SO2 and SO3 . Sulfur dioxide is produced by the combustion of fossil fuels such
as coal and from the processing of sulfide ores at smelters.
2ZnS(s) + 3O 2 (g) → 2ZnO(s) + 2SO2 (g) smelting an ore
Coal and petroleum contain between 1% and 5% S. Combustion of sulfur in fossil fuels yields SO2 .
S(s) + O2 (g) → S O 2 (g) combustion of sulfur Once in the atmosphere some of the sulfur dioxide is oxidized...
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This note was uploaded on 09/15/2009 for the course CHEM 102 taught by Professor Bastos during the Spring '08 term at Adelphi.
- Spring '08