Characteristics of the Environment - Field Sampling: Principles and Practices in Environmental Analysis - page 25

terminology the atmosphere has three layers—the troposphere, stratosphere, and
ionosphere. Newer terminology divides it into five layers—the troposphere, stratosphere,
mesosphere, thermosphere, and exosphere. This terminology stems from space
exploration and extends the atmosphere much further than 80 km out into space. If one
looks at the atmosphere from space when it is backlit by the sun, there is a reddish layer
near the Earth's surface, a lighter layer above that, and a blue layer above that.
What could the atmosphere possible have to do with field sampling? There are really
three possible answers to this question. One has to do with the occurrence and movement
of sand, silt, clay, contaminants, and particulate matter in the troposphere. The second has
to do with the amount of sunlight, particularly ultraviolet light, reaching the Earth's
surface, because some components in the soil may evaporate or vaporize into the
atmosphere or be chemically changed by light. The third is that since the atmosphere is
part of the environment it may need to be part of the field environment that is sampled [1,
2].
Air has a limited carrying capacity for most soil components. Sand cannot be picked up
by wind and moved long distances. Silt and clay can, however. Wind can carry
atmospheric contaminants long distances from their origin (e.g., the acidification of lakes
in the northeastern United States by sulfate released into the atmosphere in the Midwest).
During the dust bowl era in the United States some of the dust from the western United
States was eventually deposited in the eastern United States and Caribbean. Another
well-known example is ash from volcanoes. It can travel great distances around the Earth
if it is ejected high enough into the atmosphere. Wind can thus carry contaminants from
various sources, and these can be deposited in a field and should be of concern in any
field sampling [1, 3, 4].
Field samples exposed to sunlight for extended periods of time after being obtained
from the field can have dramatic changes in their composition. In addition, solar
radiation, rain, and wind can also affect the level of contaminant in surface soil through
evaporation or vaporization [5, 6]. Zimbabwe in south-central Africa is at an average
altitude of approximately 1.4 km. It has relatively low rainfall, usually occurring from
December through March. During the remainder of the year the sun intensity is quite high
and can affect the chemical form of contaminants found in air, water, or soil. Even during
the rainy season daytime radiation levels are frequently high. People in Zimbabwe
complain about the rapid decomposition of plastics, which is caused by the intense
sunlight. Intense solar radiation and its effects on samples are not limited to Africa and
Zimbabwe, but can be present anyplace.
The atmosphere will also have indirect effects on field sampling and the resulting
samples. These are caused by the composition of the atmosphere and can be both highly
variable and dramatic. The atmosphere is composed of nitrogen, oxygen, carbon dioxide,
argon, and water vapor plus other gases in low concentration. The nitrogen and argon
content of air is constant and inert. The water vapor, carbon dioxide, and oxygen content
varies however, and they are reactive. Changes in carbon dioxide will change the pH of
associated media, which will change the chemical form and reactivity of contaminants. In
the hydrosphere and lithosphere water vapor is less variable, while carbon dioxide and
oxygen concentrations are more variable.
On the Earth's surface the composition of atmospheric air may seem unimportant.