Snowpack photochemistry - focused on the PAN(Peroxyacetyl Nitrate) in Summit Greenland 19 April 2004 Saewung Kim

Is (Ant)Arctic region photochemically DEAD? Synthetic image (Apr. 7 10am EST) Probably YES - too remote - low solar intensity

It seems still alive! Species Predicted by gas phase chemistry Actual Measurement HCHO 70 pptv 200 pptv CH3CHO 40 pptv 80 pptv NOx 1 pptv 25 pptv HONO 20 pptv HOx 0.9 pptv 3.7 pptv (Domine and Shepson, 2002) Summit, Greenland region -Measurement data could not be explained by gas phase only prediction -The difference of each species seems non-linear  the difference is not just come from the numerical calculation. We can assume some other chemical mechanism would be going on the snowpack region.

What is the invisible hand? HETEROGENEOUS chemistry inside of the snowpack! (Domine and Shepson, 2002)

Snowpack photochemistry -Nitrate photo dissociation NO3-+h  NO2- + O (3P) h  NO2- + O- O- Channel O- + H+  OH NO2- + H+  HONO NO2- + h   NO + O- O(3P) Channel O(3P) + O2  O3 O(3P),OH,O3 + DOM  Carbonyl Compound (Domine and Shepson, 2002) Red arrow : Inside of snowpack Green arrow : Gas phase Chem.

Is this mechanism really big deal?? I Sure!! in two aspects First nearly 50% of N Hem. is covered by snow (Robinson et al., 1993) The global budget of photochemically active species would be significantly affected

Ice core research homepage Is this mechanism really big deal?? II Ice core research homepage http://www.secretsoftheice.org/icecore/ If ion species is perturbed by the heterogeneous mechanism, what we understand of the paleo-environment reconstructed by icecore interpretation would be wrong.

Importance of PAN in arctic environment I PAN in the snowpack environment will be studied ◉ PAN is the product of peroxy radical came from VOC and NOx CH3CH(O)OO + NO2+M CH3CH(O)OONO2+M Long-range transport at low T PAN PAN Thermal Decompo. CH3CHO + OH -> CH3CO + H2O CH3CO + O2 + M -> CH3C(O)OO + M CH3C(O)OO+NO2+M -> PAN + M PAN -> CH3C(O)OO + NO2 CxHy NOx HNO3 NOx HNO3 Deposition NOx Source Region Remote Region

Importance of PAN in arctic environment II Source of nitrate ion in the snowapck HNO3 : Easily soluble. But concentration is too low to explain the high concentration of nitrate ion in the snowpack. Then what is the most abundant reactive nitrogen species (NOy) in arctic environment - PAN PAN is most abundant species in the Arctic region, so the mechanism for dissolution to snow of PAN have been studied but the processes are not clearly understood (Ford et al, 2002) Simple box-model for PAN in the Summit Greenland region Understand of PAN budget in the Arctic region How much of PAN could contribute for nitrate in the snow

Box model-step I No icepack chemistry Long range transport (T) Wang et al(1998) - global Chem-Transport model Boundary layer Thermal decomposition (lifetime 76day at 255K) PAN(133pptv) July August 133ppt 132ppt Adsorption to snow (lifetime 1.3 day at 255k) Snowpack  Steady-State Assumption d[PAN]/dt = (Long range transport) – (Thermal decomp.) – ( Ads. to snow) = 0 (Long range transport) = 1.1910-3 ppt/sec

Production from snowpack Box model-step II With icepack chemistry Long range transport (T) Ford et al(2002) -Measured PAN: 74pptv -Production from snowpack : 2.0X10-2 ppt/sec Boundary layer Production from snowpack 2.0 10-2ppt/sec PAN(75pptv) TD ADS Missing Sink Snowpack d[PAN]/dt = (Long range transport) – (Thermal decomp.) – ( Ads. to snow) +(Production from snowpack) -(Missing sink) = 0 (Deposition) = 1.1910-3 ppt/sec

Deposition velocity of PAN based on box-model calculation Boundary layer = 100m(Helmig et al,2002) Snowpack Deposition velocity : how fast molecules will be deposited at given flux and concentration. (column height) = (boundary layer height)=100 m Calculated result = 3 cm/sec Huge value compared with HNO3 deposition velocity 0.5 cm/sec (Seinfeld and Pandis, 1997)

Summary and conclusion Snow covered region in high latitude could be important role in global perspective photochemistry PAN is the most abundant species in Summit Greenland region, and also important NOy species in other (Ant) Arctic environment. PAN could be role of the dominate nitrate source in Greenland region from the box model. More study is needed specific physical-chemical mechanism of PAN dissolution on ice.