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

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

3. 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.

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

5. 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.

6. 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

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

8. 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

9. 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

10. 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

11. 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

12. 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)

13. 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.