Organics in the Atmosphere from Natural Sources

The quantities of organic chemicals emitted into the atmosphere from natural sources exceed those emitted as pollutants from the anthrosphere. This ratio is primarily the result of the huge quantities of methane produced by anoxic bacteria in the decomposition of organic matter (represented as 

Flatulent emissions from domesticated animals, arising from bacterial decomposition of food in their digestive tracts, add about 85 million metric tons of methane to the atmosphere each year. Anoxic conditions in intensively cultivated rice fields produce large amounts of methane, perhaps as much as 100 million metric tons per year. Methane is a natural constituent of the atmosphere and is present at a level of about 1.8 ppm in the troposphere. 

Methane in the troposphere contributes to the photochanical production of carbon monoxide and ozone. The photochemical oxidation of methane is a major source of water vapor in the stratosphere. 

FIGURE 7.7 Some of the more important terpenes emitted by plants and an oxidation product of a-pinene. 

Many different ester compounds are released to the atmosphere by plants as shown by the following example of citronellyl formate. Although the quantities of esters released are small, they are largely responsible for the fragrances of plants and their flowers and fruits. 

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