Transcript Abating Global Ozone Pollution with Methane Emission Controls EMEP Second Meeting of the Task Force on Hemispheric Transport of Air Pollution Moscow, Russia Arlene M.

Abating Global Ozone Pollution
with
Methane Emission Controls
EMEP Second Meeting of the Task Force on
Hemispheric Transport of Air Pollution
Moscow, Russia
Arlene M. Fiore
J. Jason West
Larry W. Horowitz
June 7, 2006
Radiative Forcing of Climate, 1750-Present:
Important Contributions from Methane and Ozone
IPCC [2001]
Level of scientific understanding
Air quality-Climate Linkage:
CH4, O3 are important greenhouse gases
CH4 contributes to background O3
Free Troposphere
hn
O3
NO2
NO
OH
HO2
Global Background O3
Direct Intercontinental Transport
Boundary layer
(0-3 km)
VOC, CH4, CO
NOx
NMVOCs
CONTINENT 1
air pollution (smog)
O3
air pollution (smog)
OCEAN
NOx
NMVOCs
CONTINENT 2
O3
Observations indicate historical increase in background
ozone; IPCC scenarios project future growth
Ozone at European mountain sites
1870-1990 [Marenco et al., 1994]
Change in 10-model mean July
surface O3 [Prather et al., 2003]
2100 SRES A2 - 2000
Attributed mainly to increases in methane and NOx
[Wang et al., 1998; Prather et al., 2003]
Rising background O3 has implications
for attaining air quality standards
Pre-industrial
background
20
new CA
standard
8-hr avg
Europe
seasonal
40
Current background
60
WHO/Europe
8-hr average
80
U.S. 8-hr
average
100
O3 (ppbv)
Analyses of surface O3 from North American and European
monitoring sites indicate increasing background in recent years
[Lin et al., 2000; Jaffe et al., 2003, 2005; Vingarzan, 2004;
EMEP/CCC-Report 1/2005 ]
Impacts of O3 precursor reductions on global surface O3
Steady-state change in 8-hr daily maximum surface O3
averaged over 3-month “O3 season”
from 20% reductions in global anthropogenic emissions
NOx
NMVOC
ppbv
CO
CH4
MOZART-2 model (2.8° x 2.8°)
ppbv
West et
al., submitted
Double dividend of methane controls:
Improved air quality and reduced greenhouse warming
AIR QUALITY:
Change in population-weighted
mean 8-hr daily max surface O3
in 3-month “O3 season” (ppbv)
CLIMATE:
Radiative Forcing (W m-2)
NOx
 OH 
CH4
20% 20% 20%
anth. anth. anth.
NMVOC CO
CH4
20%
anth.
NOx
20% 20% 20% 20%
anth. anth. anth. anth.
NMVOC CO
CH4 NOx
Steady-state results from MOZART-2
 Abating O3 with CH4 controls yields largest climate benefit
West et al., submitted
Impacts of O3 Precursor Reductions on
U.S. Summer Afternoon Surface O3 Frequency Distributions
GEOS-Chem Model Simulations (4°x5°)
West & Fiore, ES&T, 2005
Contributions from precursor emissions to the
tropospheric O3 burden also add linearly
Decrease in global tropospheric O3 inventory (Tg)
in GEOS-Chem model (4°x5°)
from 50% global reductions in anthropogenic emissions
CO VOC
NOx
CH4
NOx
+
VOC
ALL
 Anthropogenic emissions of NOx and methane have the largest
impact on tropospheric O3
Fiore et al., GRL, 2002
Global observations of atmospheric CH4
NOAA/GMD cooperative
network of background
sampling sites (1983-present)
e.g. Dlugokencky et al., 2005
Column-averaged CH4
volume mixing ratio
(Aug-Nov 2003)
Frankenberg et al., Science, 2005
SCIAMACHY
 Space-based observations may provide new constraints on the CH4 budget
Estimates of current CH4 emissions
Total CH4 source ~600 Tg yr-1, ~60% anthropogenic [IPCC TAR]
>25% uncertainty in present-day CH4 sources
anthropogenic
c/o Michael Raupach, CSIRO, Australia; studies cited in IPCC TAR, AR-4
Methane sink (OH) also ~30% uncertain [Stevenson et al., 2006]
Emission estimates for the past decade are fairly
consistent with surface CH4 observations
Transient, full-chemistry simulations with MOZART-2 (1.9° x 1.9°)
driven by 1990-2004 NCEP
1790
Methane (ppb)
1780
1770
1760
1750
1740
OBS[NOAA/GMD]
BASE
VARY
1730
1720
1710
1990
1995
2000
BASE (constant emissions):
captures observed rise,
then flattening
meteorologically-driven
(OH & T)
2005
VARY (increasing EDGARYear
3.2 + time-varying wetland emissions) improves:
 Global mean surface concentration
 Interhemispheric gradient
 High N latitude seasonal cycle
Fiore et al., GRL, in press
Atmosphere gradually responds to decreases in CH4 emissions
following the CH4 perturbation lifetime (~12 years)
0
0
-50
Model approaches new steady-state
after 30 years of simulation
-100
-2
-4
-150
-200
-6
-250
-8
-300
-10
-350
-400
-12
1
6
11
16
21
26
Does the spatial pattern of the O3 decrease
depend on CH4 source location?
31
Tropospheric Ozone Burden (Tg)
Surface Methane Concentration
(ppb)
Change in methane and ozone in MOZART-2 model (1.9° x 1.9°)
Surface Methane
Tropospheric
burden by 30%
when global anthrop.
CH4 emissions
are O3
reduced
Change in global July surface O3
mainly independent of CH4 source location
Results from 11th year of transient simulation beginning in 1990 (met. year 2000)
Zero anth. CH4 emis. from Asia
30% decrease in global anth. CH4 emis.
ppbv
Zero Asia – global 30%
 Slightly larger response in
source region
 Stronger response in high-NOx
and downwelling regions
ppbv
MOZART-2 model (1.9° x 1.9°)
Tropospheric O3 responds approximately linearly to
anthropogenic CH4 emission changes across models
MOZART-2 (this work)
TM3 [Dentener et al., ACP, 2005]
GISS [Shindell et al., GRL, 2005]
X GEOS-CHEM [Fiore et al., GRL, 2002]
IPCC TAR [Prather et al., 2001]
Anthropogenic CH4 contributes:
 ~50 Tg (~15%) to tropospheric O3 burden
 ~5 ppbv to surface O3
Will methane continue to increase in the future?
Anthropogenic CH4 emissions (Tg yr-1)
Dentener et al., ACP, 2005
Future CH4 controls complement reductions in other O3 precursors
Change in mean 2020-2030 surface O3 in TM3 model (7.5° x 10°)
CH4 controls only
CO,NOx,NMVOC controls only
+
O3 change from controls on all precursors
≈
 O3 changes from all precursor reductions add
approximately linearly
Dentener et al., ACP, 2005
Conclusions: Abating O3 pollution with CH4 controls
• Anthropogenic CH4 contributes ~5 ppb to surface O3;
~50 Tg to tropospheric burden
• O3 responds approximately linearly to CH4 reductions, and to
combined changes in CH4 and other precursors
 CH4 controls complement NOx and NMVOC controls
• CH4 source location has little influence on O3 production;
heterogeneities arise from NOx distribution and transport
 Target cheapest CH4 controls worldwide
• Reducing CH4 emissions decreases surface O3 everywhere and
lowers radiative forcing (decadal time scale)
 CH4 controls could offset positive forcing from NOx controls
Remaining challenges:
• Better constraints on emissions, anthropogenic vs. natural
• Role of global change on future atmospheric CH4
Unpublished work funded by NOAA, NASA and Luce Foundation (with CATF)