H2 Light but problematic

Surface emissions include technological sources (industry, transportation and other fossil fuel combustion processes), biomass burning, nitrogen fixation in soils and oceanic activity and totals 39 Tg yr F The photochemical production (31 Tg yr ) from HCHO photolysis accounts for about 45% of the total source of H2. 

Soil uptake (55 Tg yr i) represents a major loss process for H2 and contributes 80% of the total destruction. H2 oxidation by OH in the troposphere contributes the remainder. The global burden of H2 in the atmosphere is 136 Tg. Its overall lifetime in the atmosphere is 1.9 years (Hauglustaine and Ehhalt 2002). H2 is rather well mixed in the free troposphere. However, its distribution shows a significant seasonal variation (Fig. 2.90) in the lower troposphere where soil uptake dominates. This loss process shows a strong temporal variability and is maximal during summer. 

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