1. Linking Ozone Pollution and Climate Change:
The Case for Controlling Methane
Arlene M. Fiore
Hemispheric Air Pollution Workshop
Bad Breisig, Germany
October 8, 2002
Fiore, A.M., D.J. Jacob, B.D. Field, D.G. Streets, S.D. Fernandes, C. Jang in press, Geophysical Research Letters

2. Tropospheric ozone links air pollution & climate change (1) primary constituent of smog in surface air [NRC, 1991] (2) 3rd most important greenhouse gas [IPCC, 2001] O3
Free Troposphere hn
NO2 NO
Global Background O3 OH
HO2
Intercontinental Transport
Boundary layer
(0-2.5 km)
VOC, CH4, CO
Chemical loss
Deposition
NOx
NMVOCs
NOx
NMVOCs O3 O3
CONTINENT 1
CONTINENT 2
OCEAN

3. U.S. ozone abatement strategies evolve as our understanding of the surface O3 problem improves
O3 smog recognized
as an URBAN problem: Los Angeles,
Haagen-Smit identifies
chemical mechanism
Smog considered
REGIONAL problem;
role of biogenic
VOCs discovered
A GLOBAL perspective:
role of intercontinental
transport, background
1980s
Present
1950s
Abatement Strategy:
NMVOCs
+ NOx
+ CH4??

4. TOOL: GEOS-CHEM 3D Tropospheric Chemistry Model [Bey et al., 2001]
QUESTION: Can we simultaneously mitigate air pollution and greenhouse warming?
TOOL: GEOS-CHEM 3D Tropospheric Chemistry Model [Bey et al., 2001]
(uses assimilated meteorology; 20 s; 4ºx5º or 2ºx2.5º horiz. resn.)
MODEL EVALUATION:
Mean July p.m. O3 (ppbv) in U.S. surface air
Model Bias: 2 ppbv, r2 = 0.7
GEOS-CHEM captures: regional high-O3 episodes, observed O3 vs. (NOy-NOx),
observed tightening of O3 distribution from 1980 to 1995
[Fiore et al., JGR, August, 2002]

5. What is the anthrop. contribution to global emissions?
METHOD: Use GEOS-CHEM to conduct a series of sensitivity simulations with perturbed emissions
1. Reduce various combinations of anthrop. emissions by 50% globally relative to 1995 base year
CH4 fixed at steady-state global uniform concentration
(1700 ppbv for 1995)
What is the anthrop. contribution to global emissions?
NOx ~ 65% %
CO ~ 50% %
VOCs ~ 12% %
CH4 ~ 60% %
Perturbations to
total emissions
when anthropogenic
are halved (
1000 ppbv)

6. GLOBAL increase USA decrease
METHOD (continued):
2. Implement IPCC A1/B1 future emission scenarios for 2030
A1 2030
Percent change in anthrop.
emis. from 1995 base case to 2030 simulations:
GLOBAL increase
USA decrease
NOx CO
VOCs
CH4
B1 2030

7. Change in radiative forcing
Change in radiative forcing* (W m-2) from O3 and CH4 relative to 1995 base case
NOx  OH 
CH4
50%
anthr.
NMVOC
50%
anthr.
CH4
50%
anthr.
NOx
2030 A1
2030 B1
*calculated from changes in global CH4 concentrations [IPCC, 2001]
and changes in the mean tropospheric O3 column [Mickley et al., 1999]

8. Change in summer afternoon O3 in surface air over the U.S.
Relative to 1995 base year (mean 51 ppbv, background 23 ppbv)
Mean O3
Background O3*
Degradation of U.S.
air quality from rise
in global emissions
despite domestic
reductions
Change in O3 (ppbv)
50%
anthr.
NMVOC
50%
anthr.
CH4
50%
anthr.
NOx
2030 A1
2030 B1
*produced outside the North American boundary layer (surface-760 hPa)

9. Impacts of Emissions Perturbations on U.S. Air Quality
Number of summer grid-square days
with O3 > 80 ppbv
Increase in U.S.
pollution events
despite domestic
decline in anthrop.
emissions
50%
anthr.
VOC
50%
anthr.
CH4
50%
anthr.
NOx
2030 A1
2030 B1
1995
(base)

10. Rising emissions from developing countries lengthen the O3 pollution season in the United States
1995 Base Case
2030 A1

11. Methane emissions reductions lower global O3 background and improve air quality everywhere
Free Troposphere
CH4 emissions
global impact:
Lower background O3
Negative radiative forcing
CH4
Intercontinental transport,
global O3 background
increases in
2030 A1 simulation O3
Boundary layer
(0-2.5 km)
NOx emissions local impact;
little effect on climate
Chemical loss
Deposition
NOx
NMVOCs
NOx
NMVOCs O3 O3
CONTINENT 1
CONTINENT 2
OCEAN

12. IPCC Projections of Future Methane Emissions to 2050
900
Scenarios
A1B
A1T
A1F1 A2 B1 B2
IS92a
800
CH4 emissions (Tg CH4)
700
600
2000
2040
2020
Year
Can we aim to decrease CH4 emissions?

13. WHAT ARE TAGGED OZONE TRACERS?
Standard Model: NOx + hydrocarbons  POx (archive 24-hr avg rates)
Tagged Tracer Model: O3(total) = O3(FT) + O3(NABL)+ O3(PacBL) + …
Tropopause
POx
O3(FT)
Free Troposphere
~3 km
POx
O3(PacBL)
O3(NABL)
POx
Boundary Layer
Boundary Layer
Pacific Ocean
North America
Background = O3(FT) + O3(PacBL) + … = O3(total) - O3(NABL)
(Ox = O3 + O + NO2 + 2NO3 + PANs + HNO4 + 3N2O5 + HNO3)

14. Number of summer grid-square days
with O3 > 70 ppbv
500
400
Increase in U.S.
pollution events
despite domestic
decline in anthrop.
emissions
300
200
100
1995
(base)
50%
anthr.
NMVOC
50%
anthr.
CH4
50%
anthr.
NOx
2030 A1
2030 B1