The Earth's Electrical Environment (1986)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

THE ROLE OF LIGHTNING IN THE CHEMISTRY OF THE ATMOSPHERE 75 at a combined rate of about 30 tg of N/yr (Crutzen, 1983). It is for this reason that NO x levels in urban areas are some 104 to 105 times higher than in remote regions of the marine atmosphere (McFarland et al., 1979) and in conjunction with the anthropogenic release of non-methane hydrocarbons is the cause of photochemical smog and related air pollution problems. Nevertheless, it is interesting to note that even the extremely low levels of NO x that are characteristic of the remote troposphere are believed to have a significant effect on the chemistry of the atmosphere, catalyzing the photochemical production of tropospheric O3 and enhancing OH levels (Logan et al., 1981; Davis and Chameides, 1984). To the extent that lightning is responsible for the NO x levels in the remote troposphere, it would appear that lightning plays an important role in the photochemistry of the atmosphere. OTHER TRACE GASES PRODUCED BY LIGHTNING While NO has received the bulk of the attention with regard to production by lightning because of its importance in the photochemistry of the atmosphere, research has revealed that a myriad of other trace gases in addition to NO can be generated by lightning in a variety of interesting environments. These gases and their yields in electrical discharges as determined by both theoretical calculations and laboratory experiments are listed in Table 6.3. The comparison between experimentally and theoretically derived yields is quite good over a wide range of gases and atmospheric compositions. The production of HCN in a reducing, prebiological terrestrial atmosphere is of particular interest because it has been proposed that lightning-produced HCN was an TABLE 6.3 Calculated and Experimentally Derived Yields of Trace Gases in Various Atmospheres a Species Calculated Yield (molecules/J) Experimental Yield (molecules/J) Reference A. Present-Day Terrestrial Atmosphere NO 9 × 1016 (2-6) × 1016 1,2,3,4 CO (0.1-5) × 1014 1 × 1014 5,6 N2O (3-13) × 1012 4 × 1012 6 B. Reducing Prebiological Terrestrial Atmosphere (95% N2, 5% CH4) HCN (6-17) × 1016 ~ 1017 7,8,9,10 C. Cytherian Atmosphere (95% CO2, 5% N2) CO (1-1.4) × 1017 3 × 1016 6,11,12 NO (5-6) × 1015 4 × 1015 11,12,13 (O2 + O) (6-9) × 1016 — 11 D. Jovian Atmosphere (99.95% H2, 0.05% CH4) CO 5 × 1015 — 14,15 N2 5 × 1014 — 14,15 HCN 9 × 1013 — 14,15 C2H2 3 × 1013 — 14,15 C2H4 2 × 1012 — 14,15 HCHO 8 × 1011 — 14,15 CO2 3 × 1011 — 14,15 C2H6 4 × 1011 — 14,15 E. Titan atmosphere (97% N2, 3% CH4) HCN 1.2 × 1017 — 16 C2N2 2.5 × 1014 — 16 C2H2 7.5 × 1015 — 16 C2H4 5 × 1011 — 16 a References: 1. Borucki and Chameides (1984) 2. Chameides et al. (1977) 3. Levine et al. (1981) 4. Peyrous and Lapeyre (1982) 5. Chameides (1979) 6. Levine et al. (1979) 7. Chameides and Walker (1981) 8. Sanchez et al. (1967) 9. Bar Nun and Shaviv (1975) 10. Bar Nun et al. (1980) 11. Chameides et al. (1979) 12. Bar Nun (1980) 13. Levine et al. (1982) 14. Lewis (1980) 15. Bar Nun (1975) 16. Borucki et al. (1984)