1. How will changes in emissions and climate affect tropospheric composition in 2050?
David Stevenson
University of Edinburgh
Markus Amann, Peter Rafaj, Jim Corbett, Veronika Eyring, Peter Braesicke, Veronica Montenaro, John Pyle, Mike Sanderson, Twan van Noije, Oliver Wild, Guang Zeng
Thanks to all the ACCENT Photocomp & Royal Society modellers

2. What controls tropospheric O3?
Chemistry (global precursor emissions, year 2000): ?
Anthropogenic
Biomass burning
Natural
NOx
62%
16%
11% Soils
11% Lightning
CH4
57% 6%
37% (mostly wetlands)
VOCs 4%
80% Veg. C5H8 CO
44%
47%
9% (Veg/ocean)
Main human controls
Likely to be affected by climate change

3. What controls tropospheric O3?
Physical climate variables/processes
Temperature and humidity (chemical fluxes)
Stratosphere-troposphere exchange
Clouds & precipitation (UV fluxes, wet removal)
General circulation (long range transport)
ENSO, NAO, blocking frequency, storm tracks, BL ventilation
Biological processes
Vegetation amount, distribution, speciation
Stomatal functioning
Many will/may change as climate changes

4. Anthropogenic NOx emission scenarios 2000-2100
SRES B2
SRES A2
IIASA CLE
IIASA CLE 2050
(+Climate Change)
IIASA ‘current legislation’
IIASA MFR
ACCENT Photocomp runs
Royal Society runs
Courtesy Markus Amann, IIASA

5. Ship and aircraft emissions
Both have essentially no legislation to regulate them
Likely to keep increasing if nothing is done
Ships a particularly large NOx source
In the 2050 scenario used here, we optimistically assumed that ship emissions will be controlled…

6. Future projections of ship NOx emissions
4 lines for each colour are different economic growth scenarios.
SRES B2 (=CLE basis) is 2nd line down
I chose to use TS2 (green) This gives a 50% reduction in ship NOx 2000 to 2050.
Upper scenario is more consistent with ‘current
legislation’
Eyring et al 2005

7. NOx emissions
Ships x 0.5
W. Europe x 0.41
N. America x 0.23
China x 1.03
Reduce almost everywhere – global total down ~40%

8. Anthropogenic NOx emission scenarios 2000-2100
SRES B2
SRES A2
IIASA CLE
IIASA CLE 2050
(+Climate Change)
IIASA ‘current legislation’
IIASA MFR
ACCENT Photocomp runs
Royal Society runs
Courtesy Markus Amann, IIASA

9. ACCENT models ensemble mean JJA surface O3 changes
under
three scenarios:
IIASA CLE
IIASA MFR SRES A2
IIASA CLE
IIASA MFR
SRES A2

10. Anthropogenic NOx emissions scenarios 2000-2100
SRES B2
SRES A2
IIASA CLE
IIASA CLE 2050
(+Climate Change)
IIASA ‘current legislation’
IIASA MFR
ACCENT Photocomp runs
Royal Society runs
Courtesy Markus Amann, IIASA

11. Peak surface O3 season changes
Impact of IIASA CLE 2050
emissions changes only
(relative to 2000)
Impact of climate change from only (HadGEM SRES A1B)

12. Impact of climate change (via increased water vapour) is NOx dependent
High NOx
Low NOx
More water vapour in high NOx environments increases O3
More water vapour in low NOx environments reduces O3

13. Compare responses to climate change in 3 models
Strong increases in lightning NOx in mid-latitudes (up to +50%).
Smaller increases/ little change/ decreases in tropics.
Global increase of +1 to +10%

14. Upward mass fluxes through ~70 hPa level in the tropics
Strengthening Brewer-Dobson circulation is a robust feature of transient climate runs
Upward mass fluxes through ~70 hPa level in the tropics
(Butchart et al., 2006)
The stratospheric source of tropospheric ozone will increase

15. Conclusions
Anthropogenic emissions will be the main control on near-future tropospheric ozone
Stringent controls would bring major benefits for AQ and climate
Ships (and aircraft) not currently regulated
Climate change influence is complex and uncertain
More water vapour will reduce O3 in remote regions, but increase O3 in polluted regions
STE will increase
Lightning will increase in mid-lats (decrease in tropics?)
Changes in the biosphere (biomass burning, land-use change) only just starting to be modelled