Summary

Table 16 summarizes our discussion of atmospheric trace gases. In this table, besides source strengths and burdens, the relative rates of biological and anthropogenic production expressed as a percentage of global source intensities is also given. Concerning the tabulated values we have to mention that the fraction of hydrogen and carbon monoxide from methane is considered biological. The same is true for the total ozone formed from 02 released by the biosphere (see Chapter 2). Furthermore, the global NOz source is taken as the sum of NO produced by the biosphere and N02 emitted by man. The biological portion of S02 is provided by the oxidation of H2S. The question-marks denote that the possible anthropogenic fraction is uncertain or low.

One can clearly see from the data tabulated that the preponderance of trace gases is of biological origin. They are mostly produced by microbiological processes (for further details see Schlegel, 1974). This means that the biosphere plays an important role not only in cycling the main atmospheric constituents, but also in the production of different trace gases. It is interesting to note that, while the production rate of the highly variable gases (e.g. NH3, N02, S02) is comparable to that of some variable components (N20, H2), their atmospheric burden is much smaller. This fact is due to the very short residence time caused by aerosol formation and wet deposition.

Finally, it can also be seen that the inventory of certain trace constituents is considerably modified by human activity (H2, CO, N02, S02). The anthropogenic proportion is particularly high in the case of sulfur dioxide, which yields an essential fraction of tropospheric aerosol particles (see Chapter 4). This inadvertent effect can be very dangerous from the point of view of climatic variation (see Chapter 6).

Table 16

Production rate (F) and atmospheric burden (M) of trace constituents on the basis of data of different authors (see text). Figures expressed as percentage of F give the relative source strengths due to biological and anthropogenic (in paren theses) sources

Production rate (F) and atmospheric burden (M) of trace constituents on the basis of data of different authors (see text). Figures expressed as percentage of F give the relative source strengths due to biological and anthropogenic (in paren theses) sources

H 2 20-25 40- 50 (50-60) CH4 500-1000 95-98 (2- 5) CO 1000 -501-50)

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