1. Effects of 2000-2050 global change on U.S. ozone air quality
Shiliang Wu (Harvard)
Loretta J. Mickley (Harvard)
Daniel J. Jacob (Harvard)
David Rind (NASA/GISS)
David G. Streets (ANL)
AGU Fall meeting, 2006
work supported by the EPA-STAR program

2. Background - We are facing rapid global change
1. Anthropogenic emissions of ozone precursors
2. Climate change
IPCC [2001]
Probability of max 8-h O3 > 84 ppbv
Ozone air quality correlates strongly with temperature
Lin, et al. [Atm. Env ]
IPCC [2001]

3. Models and future scenarios
Chemistry, transport, deposition, etc
GHG
Air pollutants & their precursors
Climate Change
GISS GCM III
23 vertical layers extending to 85 km
Horizontal resolution of 4º x 5º
GEOS-Chem
detailed ozone-NOx-VOC-aerosol chemistry
Anthropogenic emissions (IPCC A1B scenario)
Natural emissions
Radiative forcing
Simulated changes in global annual mean surface temperature = + 1.7oC

4. A1B 2000-2050 changes in NOx emissions
Global
U.S.
Present
Future
Change
NOx (fossil fuel), Tg N/yr
24.6
47.3
92%
5.9
3.6
- 39%
NOx (biomass burning), Tg N/yr
6.5
8.1
25%
0.03
0.06
100%
NOx (lightning), Tg N/yr
4.9
5.8
18%
0.14
0.17
21%
NOx (soil), Tg N/yr
6.1
6.6 8%
0.35
0.39
11%
fossil fuel
Growth factors for NOx emissions (future / present)
Biomass burning
4 groups of simulations
Anthropogenic emissions
Climate
Present
Future

5. Effects of 2000-2050 global change on U.S. ozone air quality
Daily max 8h-avg ozone averaged over JJA (ppb)
Present-day conditions
Effects from climate change
Effects from emission change
Combined effects
Increase of summer max-8h-avg ozone by 2-5 ppb in large areas of U.S. due to climate change.
Less effects in western U.S. because (1) anthro. emissions there are low (2) increase of ozone from inter-continental transport.

6. Factors causing worse O3 AQ with the future climate
Higher temperature
More soil NOx emissions (+21%)
Lower mixing depth
More lightning NOx emissions (+11%)
Less convection
More isoprene emissions (some areas)
Change of surface Temp. (future – present)
Change of convective mass flux at 850 hPa (future/present)
Change of afternoon PBL
(future / present)

7. Cumulative probability distributions of max 8-hr ozone (JJA)
global change has more effect on the pollution events than on the means
Cumulative probability (%)
Cumulative probability (%)
Max. 8-hr-avg ozone
Max. 8-hr-avg ozone
Present
Future climate
Future emissions
Future climate & emis
Midwest
Northeast
Cumulative probability (%)
Midwest
Southeast
Northeast
Cumulative probability (%)
Max. 8-hr-avg ozone
No effects from climate change?
Southeast

8. Why is SE U.S. ozone insensitive to climate change?
Competing effects of isoprene on ozone
Isoprene + OH RO2 (OH sink)
RO + NO2 (O3 formation) O3
RO2 + NO
RONO (sink for NOx) O3
Isoprene + O M (O3 sink)
Isoprene emissions
Isoprene emis +30%  Δ(O3)
present
future / present

9. Mitigation of climate penalty by emission reductions in ozone precursors
“climate penalty” for ozone air quality = Δ[O3] from climate change
(ppb)
Present emissions
Future emissions
Change of summer average max-8h ozone due to climate change
Reductions of anthropogenic emissions significantly mitigate the “climate penalty” and can even turn it into a “climate benefit” in southeast and northwest U.S.

10. Mitigation of climate penalty by emission reductions - continued
Regional average summer max-8h ozone (ppb)
Climate penalty is turned into climate benefit by emission reductions
“climate penalty”
Climate penalty is mitigated by emission reductions
Q: Is climate change bad for O3 AQ?
A: That depends.
With present-day anthropogenic emissions – BAD for most places.
With the reduced anthropogenic emissions – Not that bad; or even GOOD for some regions (e.g. southeast and northwest)!

11. Effects of 2000-2050 global change on Policy Relevant Background (PRB) ozone
PRB ozone = Ozone levels that would exist in the absence of anthropogenic emissions from U.S., Canada and Mexico
Decrease of background ozone in response to climate change except in the middle U.S. where NOx emissions from soil increases.
Present-day
Effects from climate change
Effects from emission change
Combined effects
Fossil fuel and biofuel emissions over North America are turned off.
Increase of bkgd ozone, especially in western U.S., mainly due to increased inter-continental transport from Asia; increase of biomass burning over NA also contributes.

12. Conclusions
Climate change could worsen ozone air quality in U.S.; the summer average daily max-8-hr ozone is projected to increase by 2-5 ppb over large areas of U.S. due to the climate change with the IPCC A1B scenario.
Factors causing worse ozone air quality associated with the future climate include: higher temperature, less convection and lower mixing depth as well as higher natural emissions.
Reductions of anthropogenic emissions can significantly mitigate the “climate penalty” for ozone air quality, and even turn it into a “climate benefit”.
The climate change would reduce the PRB ozone in U.S. by 1-3 ppb for most areas while the changes in global anthropogenic emissions would increase the PRB ozone in U.S. by 2-5 ppb.

13. Backup – some extra slides

14. Changes in emissions of ozone precursors
Global
U.S.
Present
Future
Change
NOx from fossil fuel, Tg N/yr
24.6
47.3
92%
5.9
3.6
-39%
NOx from biofuel, Tg N/yr
2.2
2.1
-5%
0.01 0%
NOx from biomass burning
6.5
8.1
25%
0.03
0.06
100%
NOx from fertilizer, Tg N/yr
0.46
0.87
89%
0.05
CO from fossil fuel, Tg /yr
381
363 81 35
-57%
176
169
-4% 3
2.6
-13%
459
750
63%
3.4
8.4
147%
Ethane from fossil fuel, Tg C/yr
6.0 17
183% 1
0.3
-70%
Propane from fossil fuel , Tg C/yr
10.1
31.6
213%
1.5
0.7
-53%
NOx from lightning, Tg N/yr
4.9
5.8
18%
0.14
0.17
21%
NOx from soil, Tg N/yr
6.1
6.6 8%
0.35
0.39
11%
Isoprene from vegetation, Tg C/yr
430
537 28
Acetone from vegetation , Tg C/yr 43 51
19%
2.7
23%
Methane abundance, ppb
1760
2400
36%

15. Effects of climate change on global ozone
Increase of ozone in the upper tropical troposphere due to increase of lightning
Present-day
Future climate
Future emissions
Future climate and emissions
Burden, Tg
309
317 (+3%)
363 (+17%)
371 (+20%)
Lifetime, days
22.4
21.0 (- 6%)
20.6 (- 8%)
19.5 (- 13%)
Annual zonal mean ozone
Surface afternoon ozone (JJA)

16. Changes of OH Surface - summer Global – zonal - annual Present-day
Future climate
Future emissions
1.10
1.19 (+8%)
1.10 (--0%)
Global – zonal - annual

17. Changes of CO
Surface - July
Global – zonal - annual