Chemistry in the Atmosphere

Under Constuction

This is a brief discussion of topics having to do with atmospheric chemistry. The atmosphere is divided into several categories having to do with height. These are the troposphere, stratosphere, mesosphere and the thermosphere. There are many chemical reactions occuring in the atmosphere and its characteristics are complex. Two of the features of the atmosphere are its temperature as a function of altitude and its pressure as a function of altitude.

As one goes up in altitude the temperature generally drops, but at some height there is a temperature inversion. This kind of functionality also occurs at lower elevations, for example, above a city. The temperature inversion has the characteristic that it traps atmospheric chemicals (and pollutants) in a volume characterized by this height and other geometrical factors.

The pressure generally decreases with altitude according to the barometric equation

.

P is the pressure at height x
P_o is the pressure at the origin 
x is the altitude in cm
M the average molecular mass
g = 980 cm/sec^2 = the acceleration due to gravity
k_B = Boltzmann's constant
T = absolute temperature

Using this equation we obtain the following results.

height       pressure
10 Km        0.30 P_o = 228 torr

20 Km        0.092P_o = 69.9 torr

50 Km        0.0026P_o = 1.95 torr

Troposphere

  • Where the people are.
    Human activity results in the production of many chemicals into the environment. The automobile, for example, is the cause for emissions due to combustion of hydrocarbons, oxides of nitrogen, carbon monoxide, carbon dioxide and, of course, water. Medical research has determined health based limits for many of these pollutants. None of this is a simple matter. Carbon monoxide, for example is a component in the physiological chemistry in humans. On the other hand, too great a concentration can lead to death and smaller concentrations may lead to adverse health effects. Thus the necessity for scientific understanding. There is a rich chemistry in the troposphere and a lot of research has been done. A list of some common tropospheric pollutants follows.
    1. Ozone from chemistry in the troposphere due to sun light, hydrocarbons and a rich chemistry.
    2. Sulfur dioxide and sulfates from the combustion of "high" sulfur fuel.
    3. Carbon monoxide from incomplete combustion largely from automobiles.
    4. Hydrocarbons from incomplete combustion largely from automobiles.
    5. Oxides of nitrogen from the high temperature "fixing" of nitrogen. That is, the reaction N_2 + O_2 ---> 2NO occuring to a significant extent at the temperatures in power plants, internal combustion engines, etc.
    6. Carbon dioxide is one of the green house gases along with methane, ozone, water vapor, etc. Carbon dioxide exists in the atmosphere in great quantities, but humans are beginning to compete. The question: is the 10% of the atmospheric amount enough to upset the quasi-equilibrium (steady state) between the complexity of naturally occuring green house gases and the heat radiation balance of the earth?
    For information the National Air Standards are shown in the table below.

    Examples of Atmospheric Chemistry

    Acid Rain

    Tropospheric Ozone

    Stratosphere 10-50Km

    Of the

    Mesosphere 50-80Km

    Of the

    Thermosphere 80Km -

    Of the

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