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 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 Dominé 4, and Eric W. Wolff 5

Importance of HCHO in the Troposphere Radical source: HCHO+h  CO+H 2  H + CHO H +O 2  HO 2 CHO+O 2  HO 2 +CO 2HO 2 +2NO  2 OH+2NO 2 HCHO + h + 2O 2 + 2NO  2 OH + 2NO 2 + 2CO + H 2 Net: This is relatively more important at the Poles, where absolute humidities are low, so that O 3 photolysis is ineffective.

Role of Aldehydes in Ozone Destruction Radical Source HCHO+h  H+ HO 2 HO 2 +BrO  HOBr+O 2 HOBr(aq) + Br - + H +  Br 2 (aq)  Br 2 (g) + h  2 Br Bromine Radical Sink Br+O 3  BrO +O 2 BrO +BrO  2 Br+O 2 Br+ HCHO  HBr+HCO Br+ CH 3 CHO  HBr+CH 3 CO

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

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

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

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

Lamp on

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

PSE2000 Guimbaud et al., Atmos. Environ., 36, , 2002.

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?

Laboratory Experiments LN 2 Zero Air 1 mm sieve 0.25 mm sieve Water (+ nitrate, DOM) ٭ ٭ ٭٭ ٭ ٭ ٭٭ ٭ ٭٭٭ DNPH cartridge In –10°F Freezer snow Coolant Recirculating Pump h Detect carbonyls generated in snow via DNPH derivitization and UV-vis detection

Uncharacterized Cleavage Products Refractory DOM Humic and fulvic substances Labile DOM carbonyls BIOTA hv, [O] hv [O] carbonyls Marine Boundary Layer SNOW hv NO 3 - hv NO 2 + O - O - + H 2 O OH - + OH NO 3 - hv NO O NO H + HONO NO + OH hv hv, [O] [O] = OH, 1 O 2, HO 2, O 3, RO 2, etc Mopper & Stahovec, 1986 Mopper et al, 1991 Kieber et al, 1990 Matsuda et al, 1992 Sumner & Shepson, 1999 Honrath et al, 2000 So, what is happening? O + Br -  Br 2

What could generate carbonyl compounds in snow? NO 3 - NO 2 + O - OH (aq) O - + H + hvNO x shown to be produced in snow via nitrate photolysis (Honrath et al., 1999, 2000) Could OH reaction with organic matter produce carbonyl compounds?

Possible Mechanism??? RO CH 3 O CH CH – CH 2 OH OH RO CH 3 O CH CH – CH 2 O RO CH CH 3 O + HCHO + H 2 O R HO CH 3 O OH R HO CH 2 O R HO + HCHO Organic material derived from plant matter (lignin)

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

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. CH 4 ) concentrations, but variability in transport and production/mobilization of biogenic organic matter (e.g. forest fires), and deposition of other reactants/precursors, such as HNO 3. The extent to which NO x is remobilized may depend on snowpack acidity, as there may be competition between: NO 3 - +h NO 2 - +O( 3 P) NO 2 - +H +  HONO (followed by volatilization) NO h NO+O( 3 P) NO 2 - +oxidants  NO 3 -

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

AcknowledgmentsAcknowledgments 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 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