Nitrogen atmospheric burden

It has been suggested (Delwiche, 1981 Soderlund and Svensson, 1976) that in order to account for the estimated burden and residence time for atmospheric N2O, the global rate of nitrogen fixation, and consequently nitrification and denitrification, would have to be about an order of magnitude greater than current estimates. Numerous measurements have found that the ocean, at certain times and places, is supersaturated with respect to N2O (Hahn, 1981), suggesting a flux of nitrogen out of the ocean to balance the overall... 

On the basis of data obtained in the atmosphere Soderlund and Svensson (1976) propose that the atmospheric ammonia burden is 0.9 x 1061 expressed in nitrogen. For the calculation of this figure the authors mentioned assumed characteristic mixing heights for different climatic regions. This height varied between 1 and 2 km. 

A significant fraction of NH3 is converted into ammonium containing aerosol particles in the atmosphere. These particles are generally composed of ammonium sulfate, the formation of which will be discussed later (Subsection 3.5.3). We only note here that the concentration of NH4 in the lower troposphere is comparable to that of NH3 gas. Even, in the upper troposphere the particulate concentration may be greater than the level of gaseous NH3. For this reason Soderlund and Svensson (1976) speculate that the atmospheric NH4 burden is twice the global mass of NH3 (both expressed as nitrogen). 

On the right-hand side of Fig. IS the atmospheric pathways of NH3 are plotted. Values of different terms are based on the references mentioned. In the figure, NH3 and NH4 burdens are also given. All numbers are expressed in nitrogen equivalents. In the total deposition value, a dry deposition of 10 x 10b t yr-1 is postulated. It should be noted that the accuracy of the values is not better than a factor of 2 or 3. It follows from these data that the residence time of NH3 in the atmosphere is around 5 days. 

On the basis of the results of nitrate measurements in the atmosphere Robinson and Robbins (1970) calculated that the total atmospheric nitrate mass is 0.9 x 1061, which is comparable to the nitrate-nitrogen burden (C.5 x 1061) given by Soderlund and Svensson (1976). 

TABLE I Mixing Ratios and Burdens of Atmospheric Nitrogen Compounds... 

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