Transcript O 3

What will control future
tropospheric ozone?
David Stevenson
+ thanks to many others, acknowledged along the way
Tropospheric Ozone (O3)
• Not to be confused with stratospheric ozone
(same gas, different place)
About ¼ of
CO2 forcing
Ozone the air pollutant: Los Angeles smog
1950s
Ozone linked
to respiratory
diseases,
e.g., asthma
US EPA (1999)
Ozone damages
crops
Ozone impact
Chamber impact
O3 injury to wheat, Pakistan (courtesy of A. Wahid)
Ozone impact on vine leafs
Soja et al. (2004)
OTC experiments
30 km Vienna, Austria
4 treatments, CF, NF, +25 ppb, +50 ppb
Exposed for 3 years
Non-filtered (NF) air i.e. ambient
Courtesy Lisa Emberson, Stockholm Environment Institute, University of York
Ozone is a secondary pollutant
• i.e., unlike CO2, CH4, etc., it is not directly
emitted
• It is generated in the atmosphere from its
precursors by photochemical reactions
• In addition there are important physical and
biological processes that control its
distribution
• A brief summary of the main chemical and
physical processes…
Tropospheric Ozone Chemistry
Stratospheric O3
Stratosphere
ΔClimate
10-15km
Troposphere
O3 + NO → NO2 + O2
O3 + hn → O(3P) + O2
OH
O3 + hn → O(1D) + O2
NO2O(1D) + M →NO
O(3P)
O(3P) + O2HO
+M
→ O3
2
NOy
losses
O3
‘Odd
oxygen’
O(3P) O(1D)
+H2O
NO2 + hn → O(3P) + NO
ΔClimate
O3
losses
CO CH4 VOC
Dry deposition
Surface
Anthropogenic
& Natural emissions
ΔClimate
Relevant timescales for O3
• Chemical lifetime of O3:
– weeks-months in upper troposphere
– days-weeks in lower troposphere
• Tropospheric transport and mixing:
–
–
–
–
vertical convection: minutes-hours
synoptic meteorology: days
intercontinental transport: days-weeks
interhemispheric transport: ~1 year
• Chemical and transport timescales overlap:
both processes are important
Tropospheric O3 essentials
• Its not stratospheric ozone
• Greenhouse gas (¼ forcing of CO2 since 1850)
– Concentrations +50 to +100% since 1850
– (but its not in the Kyoto Protocol)
• Secondary air pollutant:
–
–
–
–
Precursors: NOx, CO, CH4, VOCs (+sunlight)
Linked to respiratory diseases, e.g. asthma
Damages crops (One estimate: £3bn/yr in Europe)
Also harms forests, natural ecosystems
• Lifetime ~weeks → regional distribution
• Ozone is not only a climate issue, but also
affects the wider environment & economy
ACCENT model intercomparison for
IPCC-AR4
• 25 different models perform same experiments
– 15 Europe:
•
•
•
•
•
•
•
•
4 UK (Edinburgh, Cambridge x2, Met. Office)
3 Germany (Hamburg x2, Mainz)
2 France (Paris x2)
2 Italy (Ispra, L’Aquila)
1 Switzerland (Lausanne)
1 Norway (Oslo)
1 Netherlands (KNMI)
1 Belgium (Brussels)
– 7 US
– 3 Japan
• Large ensemble reduces uncertainties, and
allows them to be quantified
Future tropospheric O3
• Consider 2030 – ‘the next generation’ –
of direct interest for policymakers
• 3 Emissions scenarios
– ‘Likely’: IIASA CLE (‘Current Legislation’)
– ‘High’: IPCC SRES A2
– ‘Low’: IIASA MFR (‘Maximum technically
Feasible Reductions’)
• Also assess climate feedbacks
– expected surface warming of ~0.7K by 2030
People & Organisation
• Co-ordination; N+S-deposition, Tropospheric O3
– F. Dentener, D. Stevenson
• Surface O3 - impacts on health/vegetation; web-site
– K. Ellingsen
• NO2 columns – comparison of models and satellite data
– T. van Noije, H. Eskes
• Emissions
– M. Amann, J. Cofala, L. Bouwman, B. Eickhout
• Data handling and storage (SRB; ~1 TB of model output)
– J. Sundet
• Other modellers and contributors:
– C.S. Atherton, N. Bell, D.J. Bergmann, I. Bey, T. Butler, W.J. Collins,
R.G. Derwent, R.M. Doherty, J. Drevet, A. Fiore, M. Gauss, D.
Hauglustaine, L. Horowitz, I. Isaksen, M. Krol, J.-F. Lamarque, M.
Lawrence, V. Montanaro, J.-F. Müller, G. Pitari, M.J. Prather, J. Pyle, S.
Rast, J. Rodriguez, M. Sanderson, N. Savage, M. Schultz, D. Shindell,
S. Strahan, K. Sudo, S. Szopa, O. Wild, G. Zeng
Year 2000 Anthropogenic NOx Emissions
Plot: Martin Schultz, MPI
EDGAR database: Jos Olivier et al., RIVM
Year 2000 tropospheric NO2
columns
Model
(ensemble mean)
Observed (GOME)
(mean of 3 methods)
(10:30am local sampling in both cases)
Courtesy Twan van Noije, Henke Eskes
Global NOx emission scenarios
200.0
SRES A2
160.0
120.0
CLE
80.0
40.0
MFR
0.0
1990
2000
Europe
Asia + Oceania
Africa + Middle East
SRES A2 - World Total
2010
2020
2030
North America
Latin America
Maximum Feasible Reduction (MFR)
SRES B2 - World Total
Figure 1. Projected development of IIASA anthropogenic NOx emissions by SRES world region (Tg NO2 yr-1).
Regional NOx emissions
Ships/aircraft:
Europe:
falling
Asia:
rising
1990
2000
2030 CLE
2030 MFR
USA:
~flat
unregulated;
may become
larger than any
regional source
by 2030
Figure 4. Regional emissions separated
for sources
categories
in 1990, 2000, 2030-CLE and 2030-MFR for NOx [Tg NO2 yr-1]
Biomass
burning
important
source for Africa / S. America
Emission Changes 2030 CLE - 2000
Plots: Martin Schultz, MPI
IIASA RAINS model: Markus Amann et al.
Year 2000 Annual Zonal Mean Ozone (24 models)
Year 2000
Ensemble mean
of 25 models
Annual
Zonal
Mean
Annual
Tropospheric
Column
Year 2000
Inter-model
standard deviation (%)
Annual
Zonal
Mean
Annual
Tropospheric
Column
Comparison of ensemble mean model
with O3 sonde measurements
UT
250
hPa
Model ±1SD
Observed ±1SD
JFMAMJJASOND
MT
500
hPa
LT
750
hPa
90-30°S
30°S-Eq
30°N-Eq
90-30°N
2030 CLE - 2000
+5 ppbv
2030 MRF - 2000
-5 ppbv
2030 A2 - 2000
+10 ppbv
Tropospheric O3 scales ~linearly with NOx emissions
Change in O3 burden / Tg-O3
70
60
50
40
30
20
10
0
-10
-20
-30
-20
-10
0
10
20
Change in NOx emissions / Tg-N/yr
30
Radiative forcing implications
Forcings (mW m-2) 2000-2030 for the 3 scenarios:
-23%
+37%
CLE
MRF
A2
CO2
795
795
1035
CH4
116
0
141
63
-43
155
mW / m2
1500
1000
CO2
500
0
-500
O3
CH4
O3
Impact of Climate Change on Ozone by 2030
(ensemble of 9 models)
Positive
stratospheric
influx
feedback
Negative water
vapour feedback
Mean - 1SD
Mean
Mean + 1SD
Positive and negative feedbacks – no clear consensus
Impact-based ozone
indices: AOT40
Accumulated over crop growing season (e.g. 3 months for wheat)
Courtesy Lisa Emberson
AOT40, May-June-July, mean model, ppb*hours
3000 ppb.h !!!
Change in AOT40 (CLE)
Change in AOT40 (MFR)
Change in AOT40 (A2)
Conclusions
• Tropospheric O3 will increase over most parts of the
world by 2030, following a ‘Current Legislation’ scenario
(some view this as relatively optimistic)
• O3 could be reduced if current emissions reduction
technologies were applied worldwide (wildly optimistic)
• O3 could rapidly rise under a high growth scenario with
lax emissions controls, reminding us of the
consequences of not implementing current policies
(pessimistic)
• Reductions would have clear (and quantifiable) benefits
for climate and air quality; increases have clear
detrimental impacts.
• Climate change is likely to have both positive and
negative feedbacks on ozone – model predictions are
rather uncertain as to which feedbacks dominate.
• There a clear synergies between climate and air
pollution control policies that should be exploited.