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General information on organic trace gases

In addition to the main components nitrogen, oxygen and vaporized water a large number of trace gases can be found in the atmosphere. Most of these trace gases are organic compounds from a variety of sources. The organic gas most common and most simple is methane, with a mean mixing ratio of 1.8 ppm (1 molecule to 1 million air molecules = parts per million). In addition to methane, a nearly unlimited number of other organic trace gases exist.

Hundreds of different compounds are observed in urban areas or in the exhaust flags of forest fires. Their mixing ratios are typically by many orders of magnitude smaller than methane mixing ratios. Values are in the order from ppb (1 molecule in 1 billion air molecules) to ppt (1 molecule in 1 trillion air molecules).

Substances can be separated according to their volatility by gas chromatography. In the analytical process, the substances pass through a small capillary column and can be detected individually in a detector. Each ‘peak’ in the resulting chromatogram corresponds to a substance.

Peak

However, the variety of organic trace gases in the atmosphere cannot be fully characterized even with modern analysis methods as gas chromatography and PTRMS. Previous studies have identified hundreds of different compounds in the troposphere emitted from anthropogenic and biogenic sources into the atmosphere.

The different sources of organic compounds and their distribution, but also the various transformation processes of organic compounds in the troposphere reflects the diversity of organic compounds and the complex organic composition of the troposphere.

Hydrocarbons react with a few exceptions primarily with hydroxyl radicals. The rate of this reaction determines the lifetime of organic molecules and their residence time in the atmosphere. The other reaction pathways and degradation products are as versatile as the hydrocarbons themselves.

Organic compounds are oxidized and therefore the "fuel", keeping the atmospheric photochemistry in motion. Due to their high reactivity, they play an important role in the chemistry of the atmosphere.


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