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Atmospheric chemistry Lecture 5: Polar Ozone Holes & Arctic Haze Dr. David Glowacki University of Bristol,UK

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Presentation on theme: "Atmospheric chemistry Lecture 5: Polar Ozone Holes & Arctic Haze Dr. David Glowacki University of Bristol,UK"— Presentation transcript:

1 Atmospheric chemistry Lecture 5: Polar Ozone Holes & Arctic Haze Dr. David Glowacki University of Bristol,UK

2 Over the last 4 days… Weve discussed: –Atmospheric structure & transport –Chemical kinetics –Tropospheric oxidation chemistry –Stratospheric O 3 chemistry Today were going to put the pieces together to understand… Stratospheric Polar Ozone holes (1995 Chemistry Nobel Prize) Arctic Haze (particularly bad in the Northern Hemisphere)

3 Polar O 3 holes

4

5 Polar Ozone Holes- Why do we care?

6 Polar Ozone Holes: Why do we Care? The EPA estimates that 60 million Americans born by the year 2075 will get skin cancer because of Ozone depletion UV exposure also harms plants & animals

7 October 2000 For the Second time in less than a week dangerous levels of UV rays bombard Chile and Argentina, The public should avoid going outside during the peak hours of 11:00 a.m. and 3:00 p.m. to avoid exposure to the UV rays Ushaia, Argentina The most southerly city in the world

8 Ozone loss does appear in the Arctic, but not as dramatic Some years see significant depletion, some years not, and always much less than over Antarctica Arctic O 3 measurements above Spitzbergen

9 Catalytic ozone destruction The loss of odd oxygen can be accelerated through catalytic cycles whose net result is the same as the (slow) 4 th step in the Chapman cycle Uncatalysed:O + O 3 O 2 + O 2 k 4 Catalysed:X + O 3 XO + O 2 k 5 XO + O X + O 2 k 6 Net rxn: O + O 3 O 2 + O 2 X is a catalyst and is reformed X = OH, Cl, NO, Br (and H at higher altitudes) Yesterday, we discussed OH & NO catalyzed loss What about Br & Cl catalyzed loss?

10 Catalytic O 3 loss via Cl

11 Catalytic O 3 loss at high [ClO]

12 Br + O 3 BrO + O 2 Cl + O 3 ClO + O 2 ALSOBrO + ClO Br + ClOO ClOO Cl + O 2 Net 2O 3 3 O 2 Br and Cl are regenerated, and cycle does not require O atoms, so can occur at lower altitude Sources of bromine: CH 3 Br (natural emissions from soil and used as a soil fumigant) Halons (fire retardants) Catalytic cycles are more efficient as HBr and BrONO 2 (reservoirs for active Br) are more easily photolysed than HCl or ClNO 3 But, there is less bromine than chlorine Catalytic O 3 loss via Br Br BrO Br

13 Cl in the stratosphere: Chloroflorocarbons (CFCs or Freons)

14 CFC measurements Niwot Ridge Pt Barrow Mauna Loa Am Samoa Cape Grim South Pole

15 Data from NOAA CMDL Ozone depleting gases measured using a gas chromatograph with an electron capture detector (invented by Jim Lovelock) Values in the N hemisphere slightly higher Global CFC Emissions These are ground-based measurements. The maximum in the stratosphere is reached about 5 years later

16 CFCs are not destroyed in the troposphere. They are only removed by photolysis once they reach the stratosphere. CFC transport

17 Simultaneous measurements of ClO and O 3 on the ER-2 Late August 1987September 16 th 1987 Still dark over AntarcticaDaylight returns Gas phase chemistry alone cannot explain these observations

18 Polar Stratospheric Clouds PSCs catalyze the conversion of ClNO 3 (a Cl reservoir) to Cl 2 (and eventually Cl) PSC solid phases: Formation is more likely in the Antarctic because of Lower T

19 O 3 depletion within the Antarctic vortex ClO+BrO Cl+Br+O 2 In the southern hemisphere, strong westerly winds arise from Coriolis forces because there is little land to induce turbulent mixing This results in a south polar cell (vortex) which is more isolated from southern mid- latitudes than the northern polar cell, and extreme temperature gradients – especially in winter

20 Arctic Haze

21 Possible exam trick question: Identify Los Angeles

22 Observations of Arctic Haze First observed in the 1950s during US military weather observation flights from bases in Alaska to the high Arctic G.E. Shaw, The Arctic Haze Phenomenon, Bull. Am. Met. Soc., 1995, 76(12), p

23 Arctic Haze: Pollutant Transport & buildup Pollutants from lower latitudes are transported to the Arctic are oxidized during arctic summer During polar winter, OH oxidation ceases Cold temperatures make the arctic boundary layer very stable during winter, dramatically slowing mixing

24 Arctic Haze: Pollutant Transport & buildup Peroxyacetylnitrate can transport NO 2 long distances from source Typical VOC profiles will look something like this

25 Arctic Haze: In the polar spring the sun returns… The boundary layer temperatures increase OH production begins NO 2 is released from its reservoirs [O 3 ] and [RO 2 ], and [RO] increase rapidly The chemical reactor turns ON, making a mixture of reactive chemicals and sticky peroxy radicals that can react with gas phase and aerosol species

26 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product VOC

27 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O2O2

28 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product VOC

29 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O2O2 sunlight VOC

30 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O2O2 VOC

31 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 VOC

32 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 sunlight O2O2 VOC

33 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O2O2 O3O3 O3O3

34 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 VOC

35 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O2O2 sunlight O3O3 O3O3 VOC

36 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O2O2 O3O3 O3O3 VOC

37 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 O3O3 VOC

38 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 sunlight O2O2 O3O3 O3O3 VOC

39 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O2O2 O3O3 O3O3 O3O3 O3O3

40 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 O3O3 O3O3 VOC

41 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O2O2 sunlight O3O3 O3O3 O3O3 O3O3 O3O3 VOC

42 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O2O2 O3O3 O3O3 O3O3 O3O3 O3O3 VOC

43 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 O3O3 O3O3 O3O3 O3O3 VOC

44 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 sunlight O2O2 O3O3 O3O3 O3O3 O3O3 O3O3 VOC

45 OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 O3O3 O3O3 O3O3 O3O3 O2O2 VOC

46 ARCTIC HAZE!!!!!!!!! VOC OHHO 2 RO 2 RO NONO 2 NONO 2 oxidation product O3O3 O3O3 O3O3 O3O3 O3O3 O3O3

47 Conclusions The change in light conditions from polar winter and polar summer makes for some crazy polar pollution Atmospheric transport, kinetics, and sunlight influence both stratospheric ozone loss and arctic haze The different properties of the arctic and antarctic make for different chemistry


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