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1 Purdue University, West Lafayette IN, USA

Implications of Photochemistry Involving Organic Compounds in Sunlit Snowpacks. Paul B. Shepson 1 , Amanda M. Grannas 1 , Terra M. Dassau 1 , Ann Louise Sumner 1 Jan W. Bottenheim 2 , Leonard A. Barrie 3 , Florent Domin é 4 , and Eric W. Wolff 5. 1 Purdue University, West Lafayette IN, USA

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1 Purdue University, West Lafayette IN, USA

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  1. Implications of Photochemistry Involving Organic Compounds in Sunlit Snowpacks Paul B. Shepson1, Amanda M. Grannas1, Terra M. Dassau1, Ann Louise Sumner1 Jan W. Bottenheim2, Leonard A. Barrie3, Florent Dominé4, and Eric W. Wolff5 1 Purdue University, West Lafayette IN, USA 2 Meteorological Service of Canada, Toronto, Ontario Canada 3 World Meteorological Organization, Geneva, SW 4 LGGE, Grenoble, FR 5 British Antarctic Survey, Cambridge, UK

  2. Importance of HCHO in the Troposphere Radical source: HCHO + h  CO + H2  H• + •CHO H• + O2 HO2• •CHO + O2 HO2• + CO 2HO2• + 2NO• 2•OH + 2NO2• HCHO + h + 2O2 + 2NO• 2 •OH+ 2NO2• + 2CO + H2 Net: This is relatively more important at the Poles, where absolute humidities are low, so that O3 photolysis is ineffective.

  3. Role of Aldehydes in Ozone Destruction Radical Source HCHO + h  •H + HO2• HO2• + BrO• HOBr + O2 HOBr(aq) + Br - + H+ Br2(aq)  Br2(g) + h 2 •Br Bromine Radical Sink •Br + O3 BrO• + O2 BrO• + BrO• 2 •Br + O2 •Br + HCHO  HBr + HCO• •Br + CH3CHO  HBr + CH3CO•

  4. Sumner and Shepson, Nature, 398, 230-233, 1999. The HCHO lifetime changes from ~3 months in the dark, to 0.5 days in sunlight

  5. Snowpack Interstitial Air Measurements probe support Snowpack Measurements: 30 m heated inlet line to GC/MS Air Snow Stainless Steel Open Tube ¼ PFA tubing Teflon Probe with Filter

  6. A. L. Sumner and P. B. Shepson, Nature, 398, 230-233, 1999. Gradient implies a flux out of the snowpack

  7. But Physical processes (metamorphism, T-dependent adsorption/desorption) may also be very important! Hutterli et al., GRL, 26, 1691-1694, 1999. Hutterli et al. have discussed that firn air HCHO can be explained as a result of temperature-dependent adsorption/desorption from snow grains.

  8. Lamp on

  9. ALERT2000 Grannas et al., Atmos. Environ. 36, 2733-2742, 2002. Large diel cycles observed for carbonyl compounds; not well correlated with snowpack Temperature

  10. PSE2000 Guimbaud et al., Atmos. Environ., 36, 2743-2752, 2002.

  11. But, our previous measurements all focused on observations of the gas phase, in equilibrium (or not) with the snow. Are these species really produced in snow?

  12. Laboratory Experiments In –10°F Freezer DNPH cartridge 1 mm sieve Zero Air LN2 0.25 mm sieve Water (+ nitrate, DOM) ٭ ٭ ٭ ٭ ٭ ٭ ٭ ٭ ٭ ٭ ٭ ٭ h Detect carbonyls generated in snow via DNPH derivitization and UV-vis detection Coolant Recirculating Pump snow

  13. So, what is happening? Marine Boundary Layer carbonyls hv SNOW hv O + Br- Br2 NO3- NO2 + O- [O] = OH, 1O2, HO2, O3, RO2, etc O- + H2O OH- + OH hv NO3- NO2- + O hv BIOTA NO2- + H+ carbonyls HONO hv hv [O] HONO NO + OH Mopper & Stahovec, 1986 Mopper et al, 1991 Kieber et al, 1990 Matsuda et al, 1992 Sumner & Shepson, 1999 Honrath et al, 2000 hv, [O] Uncharacterized Cleavage Products Humic and fulvic substances hv, [O] Refractory DOM Labile DOM

  14. What could generate carbonyl compounds in snow? hv NOx shown to be produced in snow via nitrate photolysis (Honrath et al., 1999, 2000) NO3- NO2 + O- O- + H+ OH (aq) Could OH reaction with organic matter produce carbonyl compounds?

  15. Possible Mechanism??? Organic material derived from plant matter (lignin) CH3O CH3O RO CH – CH2OH CH HO R •OH •OH CH3O •CH2O RO CH – CH2O• CH + H2O HO R CH3O + HCHO RO CH • CH • + HCHO HO R

  16. Photo-oxidation mechanism h Norrish type II Photofragmentation h h Carbonyl -cleavage (Norrish type I) Riemer et al, Marine Chemistry, 2000, 71, 177-198. Note: Ethene and propene production observed in snow at Summit, Greenland!!! Carbonyl compound production observed in snow at Alert, Canada!!!

  17. Implications for snow/ice core composition? If indeed carbonyl compounds within snow/ice can be produced from DOM oxidation, the snow/ice core composition would to some extent reflect not atmospheric radical (i.e. OH) and VOC (e.g. CH4) concentrations, but variability in transport and production/mobilization of biogenic organic matter (e.g. forest fires), and deposition of other reactants/precursors, such as HNO3. The extent to which NOx is remobilized may depend on snowpack acidity, as there may be competition between: NO3- + h  NO2- + O(3P) NO2- + H+  HONO (followed by volatilization) NO2- + h  NO + O(3P) NO2- + oxidants  NO3-

  18. Conclusions • No, seriously, I really think that carbonyl compounds can be • photochemically produced in sunlit snowpacks! • There are significant consequences for the snow-covered boundary • layer, and likely for ice cores, for photochemically rective species. • We need to: • better understand the DOM content of snow! • be able to quantitatively understand snow (surface?) phase • photochemistry and kinetics

  19. Acknowledgments • NSF • CFS Alert and Environment Canada, Jan Bottenheim, Len Barrie, Al Gallant, John Deary • Jack Dibb, Richard Honrath, Aaron Swanson • Purdue’s Amy Instrumentation Facility

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