1. NOx Production by Laboratory Simulated TLEs Harold Peterson NASA-Marshall Space Flight Center Matthew Bailey, John Hallett Desert Research Institute William Beasley University of Oklahoma

2. Outline Purpose of research TLEs NO x produced by discharges Experimental setup Simulations Results Conclusions

3. Why does it matter? High concentration of nitric oxide (NO) in mesosphere Mesospheric NO transported downward to stratosphere in the polar winter Stratospheric nitrogen oxides (NO x ) contributes to ozone depletion (Callis 2002) Understanding the sources of middle atmosphere NO x is prerequisite to fully understanding the causes of the ozone hole

4. Transient Luminous Events (TLEs) Several types of discharges, all occurring above thunderstorm tops Blue jets –Propagate up to 40 km –Some reach the ionosphere (gigantic jets) (Pasko et al 2002) Red sprites –Extend downward from the ionosphere to around 40 km (Lyons 2003) –Gigantic jets have sprite-like characteristics in the mesosphere

5. Summary of TLEs from Physics Today article

6. Nitrogen oxide (NO x ) production in thunderstorms Energy of lightning dissociates oxygen molecules, initiating the reaction –O 2 -> 2O Single replacement turns a nitrogen molecule and an oxygen atom into nitric oxide and a nitrogen atom –N 2 + O -> NO + N

7. Nitrogen oxide (NO x ) production in thunderstorms Single replacement turns an oxygen molecule and a nitrogen atom into nitric oxide and an oxygen atom –O 2 + N -> NO + O Reaction ends when nitrogen atoms and oxygen atoms have recombined into nitrogen molecules and oxygen molecules (Goldenbaum 1993) –2O -> O 2 –2N -> N 2

8. NO x production in TLEs Energy of TLEs is likely insufficient to thermally dissociate oxygen molecules Blue jets dissociate oxygen using accelerated electrons NO x production then follows the same reaction steps as in tropospheric discharges (Hiraki 2004)

9. NO x production in TLEs Ionized species and excited state molecules likely play a role in sprites For example, O 2 + + N 2 -> NO + NO + (Chamberlain 1978) Details of sprite reaction mechanisms are still unknown

10. Experimental setup Vacuum chamber –Maximum vacuum is 0.3 mb (30 Pa) with current setup –Allows simulation of discharges in the upper troposphere, all of the stratosphere, and the lower mesosphere Tunable pulsed power unit –Maximum DC voltage: 35 kV Power supply allows 50 kV, but safety considerations (arcing) limit the maximum to 35 kV –Maximum current: around 250 A –Switch allows user the choice of discharging voltage all at once, or slowly increasing field to breakdown strength Chemiluminescence NOx detector

11. Experimental setup

13. Simulations

14. Simulation vs. blue jet

15. Production as a function of pressure

16. Mixing ratio of NO to NO 2

17. Correction for energy dissipated in the circuit -CMAQ says NO x /J as a function of pressure is linear

18. Three production mechanisms As mentioned before, reaction mechanisms differ for tropospheric lightning vs. blue jets vs. sprites Going from higher to lower pressure, production per unit energy is: –lowest for 100 and 500 mb discharges –highest for 10 and 50 mb discharges –drops again for 1 mb discharges

19. Global sprite NO x estimate Energy method: –NO x /J from experiments, times J/sprites, times sprite frequency Geometric method: –NO x /volume from experiments, times volume/sprite based on effective streamer diameter, times sprite frequency –not as precise as energy method –details outlined in paper

20. Global sprite NO x estimate Energy method NO x /year: –Low end: 5.88*10 28 molecules/yr –High end: 1.35*10 31 molecules/yr Geometric method NO x /year: –Low end: 2.6*10 30 molecules/yr –High end: 1.7*10 33 molecules/yr Next step is to estimate ozone destroyed/created by this quantity of NO x

21. Conclusions Middle atmosphere NO x contributes to ozone hole depletion TLEs are studied in this experiment as a possible source of middle atmosphere NO x NO x production per discharge is lower for TLEs than for lightning

22. Conclusions NO x production per ampere of current is equal for TLEs and for lightning NO x production per joule of energy is greater for TLEs than for lightning Three different production efficiencies correspond to three different reaction mechanisms, each favored in their own pressure range

23. Conclusions Energy method, geometric method used to calculate sprite NO x –Overlap between ranges of values indicates most likely production amount Quantity of ozone destroyed not yet known

24. Acknowledgements Drs. Matthew Bailey (DRI) and William Beasley (OU) for their support of my research Dr. Mike Poellot (UND) for suggesting lightning-produced NO x as a possible research topic

25. Acknowledgements NSF-EPSCoR grant EPS-0082725 NSF ATM grant 0224865 NSF SGER grant 6340-663-9070 Also supported by an appointment to the NASA Postdoctoral Program at the Marshall Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA

26. References Callis, L. B., M. Natarajan, and J. D. Lambeth, Observed and Calculated Mesospheric NO, 1992-1997, Geophysical Research Letters, 29, 2, 2002. Chamberlain, Joseph W., Theory of Planetary Atmospheres: An Introduction to their Physics and Chemistry, Academic Press, New York, 330 pp, 1978.

27. References Goldenbaum, G. C. and R. R. Dickerson, Nitric oxide production by lightning discharges, Journal of Geophysical Research, 98, 18333-18338, 1993. Heavner, M.J. et al, Sprites, Blue Jets and Elves: Optical Evidence of Energy Transport Across the Stratopause, AGU Monograph 123,”Atmosphere Science Across the Stratopause”, 69-82, 2000. Hiraki, Y. et al, Generation of Metastable Oxygen Atoms (O(1D)) in Sprite Halos, J. Geophys. Res., 31, L14105, doi: 10.1029/2004GL020048, 2004.

28. References Ignccolo, M. et al, The Planetary Rate of Sprite Events, Geophys. Res. Lett., 33, L11808, doi: 10/1029/2005GL025502, 2006. Inan, U. S., Lightning Effects at High Altitudes: Sprites, Elves, and Terrestrial Gamma Ray Flashes, C. R. Physique 3, 1411-1421, 2002. Lyons, W. A., CCM, T. E. Nelson, R. A. Armstrong, V. P. Pasko, and M.A. Stanley, Upward Electrical Discharges from Thunderstorm Tops, Bull. Am. Met. Soc., 445- 454, 2003.

29. References Pasko, V. P. et al, Electrical Discharge from a Thundercloud Top to the Lower Ionosphere, Nature, 146, 152-154, 2002. Rakov, V. A. and M. A. Uman, Lightning: Physics and Effects. Cambridge University Press, Cambridge, U.K., 687 pp., 2003. Yair, Y. et al, New Observations of Sprites from the Space Shuttle, Journal of Geophysical Research, 109, D15021, doi:10.1029/2003JD004497, 2004.