Page 199 - Fundamentals of Air Pollution 3E

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Atmospheric Chemistry

Atmospheric chemistry encompasses all of the chemical transformations
occurring in the various atmospheric layers from the troposphere to beyond
the stratosphere. Air pollution chemistry represents the subset of these
atmospheric chemical processes which have a direct impact on human
beings, vegetation, and surface water bodies. Classification of atmospheric
chemical processes as either human-made (anthropogenic) or natural is
useful but not precise. For example, the trace gases nitric oxide (NO) and
sulfur dioxide (SO 2) have both anthropogenic and natural sources, and
their atmospheric behavior is independent of their source. A vivid example
was the 1980 Mt. St. Helen's volcanic eruption in Washington, a gigantic
point source for SO 2 and particulate matter in the atmosphere. This natural
source was of such magnitude as to become first a regional air pollution
problem and subsequently a global atmospheric chemical problem.

I. TYPES OF ATMOSPHERIC CHEMICAL TRANSFORMATIONS

The chemical transformations occurring in the atmosphere are best char-
acterized as oxidation processes. Reactions involving compounds of carbon
(C), nitrogen (N), and sulfur (S) are of most interest. The chemical processes
in the troposphere involve oxidation of hydrocarbons, NO, and SO 2 to