Transcript O 3 - University of Edinburgh

Modelling global
Tropospheric Ozone:
Implications for Future
Air Quality and Climate
David Stevenson
Institute for Meteorology
University of Edinburgh
Thanks to:
Colin Johnson, Dick Derwent, Bill Collins (Met. Office)
Talk Structure
• Some background about tropospheric
ozone
• Describe the chemistry-climate model
• Model comparisons with observations
• Model predictions
• The future
Tropospheric Ozone (O3)
• Air Pollutant
– City and regional-scale photochemical
smogs
– Damage to Vegetation
– Human health – attacks tissue
• Greenhouse gas
– Third most potent after CO2 and CH4
– Strong spatial variation in forcing
Photochemical Smog
Ozone Damage to Vegetation
Human health effects of
ozone
Healthy
lung
Damaged
lung
It makes you cry
Observed Ozone trends
European mountain sites
1970-1997 ozone sonde data
NH mid-latitude
free troposphere
IPCC, 2001
Radiative forcing 1750-2000
CO2
1.5 W m-2
CH4
0.5 W m-2
Trop O3 0.35 W m-2
(IPCC, 2001)
Trop. Ozone radiative forcing
1750-2000
W m-2
This is a model result
IPCC, 2001
IPCC models DO3 2000-2100
Large range,
particularly in
tropical UT
IPCC models
STOCHEM
•
•
•
•
•
•
Lagrangian chemistry-transport model
50,000 air parcels
Coupled 3 hourly to HadAM3/HadCM3
AGCM grid: 3.75° x 2.5° x 58/19 levels
CTM output: 5° x 5° x 22 levels
70 chemical species
– CH4-CO-NOx-Hydrocarbons
– Isoprene, PAN, Acetone, CH3CHO, etc.
– 5-minute chemical timestep
STOCHEM Global Chemistry Model Framework
Air parcel centres
Eulerian grid
from GCM
provides
meteorology
Interpolate met. data for each
air parcel
For each air parcel
• Advection
– 4th order Runge-Kutta Dt=1 hr
– Plus small random component (=diffusion)
• Emission & deposition fluxes
• Integrate chemistry
– Photochemistry
– Gas phase chemistry
– Aqueous phase chemistry
• Mixing
– with surrounding parcels
– convective mixing
– boundary layer mixing
Stratospheric O3
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)
NO2 + hn → O(3P) + NO
O3
losses
CO CH4 VOC
Dry deposition
Anthropogenic
& Natural emissions
Use STOCHEM to look at some of the
important factors for future European O3
•
•
•
•
•
European emissions
Northern hemisphere emissions
Mix & location of emissions
Rising levels of methane
Climate change
• Changing stratospheric ozone
• Land use change / changing ‘natural’ emissions
Modelling approach
 Repeat experiments changing only
emissions


1990 (base year)
2030 variants
 Experiments changing both emissions
and climate
 First, comparison with some
observations for the 1990s
Anthropogenic NOx emissions 1990
Global total: 24 Tg(N)
(NB excluding biomass burning)
GOME NO2: March 1997
NO2 Column Density March 1997 (1015 molecules per cm2)
P. Veefkind, KNMI
EMEP O3 monitoring sites
AOT4
0
(ppbh)
April–
Septe
mber
1999
(daylig
ht
hours)
EMEP/TOR-2
data from NILU (A-G Hjellbrekke & S Solberg)
.
Harwell monthly mean Ozone
Model – observation comparison
Surface ozone Switzerland
Good
agreement at
a rural site
Poor at a
nearby
urban site
Model – observation
comparison
Surface ozone
Scandinavia
Good agreement at 60°N
Poor in the Arctic
Observed July
daytime
mean O3 1990-99
STOCHEM 1800h
July mean O3
Modelling approach

Repeat experiments changing only emissions








1990 (base year)
2030 (IPCC SRES A2 scenario)
2030, 1990 Europe
2030, 1990 N. America
2030, 1990 Asia
CH4 in 1990: 1745 ppbv (used for all above)
Further 2030 run with CH4 at 2080 ppbv
Biomass burning & natural emissions fixed
Change in Anthropogenic NOx emissions 1990 to 2030
+0.3
+2.4
+14.3
Rest of World +13.1
Global increase: +30.1 Tg(N)
Based on
IPCC SRES
A2 scenario
IPCC
SRES
A2 scenario
Changes in other emissions 1990 to 2030
DGlobal
DEurope DN. Amer
DAsia
DROW
NOx
+30.1 +0.3 +2.4 +14.3 +13.1
CO
+287 -32
-15 +148 +186
+26
-0.3 +2.4 +23
NMVOC
+1
NOx in Tg(N) CO in Tg(CO)
NMVOC in Tg(C)
Surface Ozone changes 1990 to 2030 (no CH4 increase)
European
spring/summer
0 ppbv in North
up to +8 in S
JAN
APR
JUL
OCT
Surface DO3 1990 to 2030 – component due to European emissions
European
emissions cause
-3 to +6 ppbv
JAN
APR
JUL
OCT
Surface Ozone changes 1990 to 2030 – N. American component
N. American
emissions cause
0 to +2 ppbv
JAN
APR
JUL
OCT
Surface Ozone changes 1990 to 2030 – Asian component
JAN
APR
JUL
OCT
Vertical section
40-45°N
Asian emissions
cause
0 to +2 ppbv
Extra O3 due to regional emissions changes
Surface Ozone changes 1990 to 2030 (including CH4 increase)
European
spring/summer
~ +10 ppbv
JAN
APR
JUL
OCT
Surface Ozone changes 1990 to 2030 (excluding CH4 increase)
JAN
APR
JUL
OCT
Climate change effects
• Two mammoth 110-yr coupled
chemistry-climate runs (1990-2100)
1. Control climate; SRES A2 emissions
2. SRES A2 climate forcing & emissions
• Johnson et al. (2001 , GRL)
Climate Change effects
Surface Temperature
+3.5 K
SRES A2 climate
+3.5K
Control climate
Control climate
SRES A2 climate
Methane / ppbv
Control climate
SRES A2 climate
CH4 lifetime
Johnson et al. 2001 GRL
N. Mid-latitude surface O3 / ppbv
Control climate
SRES A2 climate
Johnson et al. 2001 GRL
Large negative
feedback due to
increases in water
vapour and O3
destruction
Ozone chemical production (July)
200 hPa
Surface
Ozone chemical loss (July)
200 hPa
Surface
O3 net chemical production (July)
200 hPa
Surface
Ozone lifetime (July)
200 hPa
Surface
Days
5
10
20
50
100
Conclusions & remaining questions
• UK spring/summer surface O3 up 6 to 10 ppbv by 2030
• European emissions:
-2 to -4 ppbv
– UK appears to benefit from emissions reductions in E. Europe
• N. American emissions:
0 to +2 ppbv
• Asian emissions:
0 to +2 ppbv
– Other N. Hem emissions counteract European reductions
• Global methane increase: +8 ppbv
– Methane increases appear very important – these are mainly
driven by developing world emissions
• Climate change may reduce surface O3
– More water vapour, more O3 destruction
• What about:
– Other emissions scenarios ?
– Changes in stratospheric ozone ?
– Changes in land-use / “natural” emissions ?
Future chemistry-climate
modelling
• Higher resolution / nested models
– Plume processing
– Boundary layer effects – surface & tropopause
– Resolved cloud processes – lightning,
convective mixing, aqueous chemistry,
washout
• More coupled processes
– Biosphere
– ENSO – biomass burning, oceanic emissions
– Emissions from and deposition to vegetation
Stratospheric O3
OH
NO2
HO2
NOy
losses
O3
NO
O(3P) O(1D)
O3
losses
CO CH4 VOC
Dry deposition
Anthropogenic
& Natural emissions