Escape of H and He

As mentioned at the beginning of this chapter, diffusive separation of low atomic or molecular weight species into space causes them to be permanently lost from the Earth. Thus, the Earth is deficient in He and H2 relative to the best estimates of initial terrestrial composition. Some species might be accreted from space certainly, micrometeorites represent a small but identifiable flux. Published speculations exist regarding other substances, notably water. However, these appear to be relatively unimportant at present. 

Chapman, S. (1930). On ozone and atomic oxygen in the upper atmosphere. Phil Mag. Ser. 710 (64), 369-383. 

Charlson, R. J. and H. Rodhe (1982). Factors influencing the natural acidity of rainwater. Nature 295, 683. 

Charlson, R. J., W. L. Chameides, and D. Kley (1985). The transformations of sulfur and nitrogen in the remote atmosphere. In The Biogeochemical Cycling of Sulfur and Nitrogen in the Remote Atmosphere (J. N. Galloway, R. J. Charlson, and M. O. Andreae, eds.), pp. 67-80. Reidel, Dordrecht, The Netherlands. 

Crutzen, P. J. (1983). Atmospheric interactions Homogeneous gas reactions of C, N and S containing compounds. In The Major Biogeochemical Cycles and Their Interactions (B. Bolin and R. Cook, eds.), pp. 67-112. John Wiley, Chichester. 

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