Substances in the climate system

All kinetic data given in the following chapters are from the lUPAC subcommittee for gas kinetic data evaluation if not otherwise cited (also Atkinson et al. 2004, 

The troposphere has an estimated 155 Tg of hydrogen gas (H2), with approximately a two-year lifetime (Chapter 2.8.2.10). Many sources of hydrogen gas and a few major sinks account for this relatively short lifetime. The main pathway in the production of hydrogen atoms in the air is the methane (CH4) conversion by the OH radical and subsequent photolysis of formaldehyde (HCHO) see reactions (5.42) to (5.48). This process accounts for about 26 Tg H yr (Novelli et al. 1999). 

Once H is formed in the troposphere H combines with O2 to produce the important 

Hugh Taylor first proposed the formation of HO2 (in the photochemical H2 + O2 reaction) in 1925 and it was detected by mass spectroscopy in 1953 (Foner and Hudson 1953). The relatively fast reaction with the HO2 radical, producing OH, can be of interest only in the stratosphere ks2 = 7.2 10 cm molecule s (298 K)  

This reaction splits in two further product pathways of minor importance  

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