1. Influence of future climate change on air quality – global model results
David Stevenson
Institute of Atmospheric and Environmental Science School of GeoSciences The University of Edinburgh
Thanks to:
Ruth Doherty (Univ. Edinburgh)
Mike Sanderson, Colin Johnson, Bill Collins (Met. Office)
Dick Derwent (rdscientific / Imperial College)
Frank Dentener, Peter Bergamaschi, Frank Raes (JRC Ispra)
Markus Amann, Janusz Cofala, Reinhard Mechler (IIASA)
Martin Schultz, Guang Zeng, Kengo Sudo, Nadine Bell, Sophie Szopa, Veronica Montenaro, Jean-Francois Lamarque + All the other IPCC ACCENT modellers
NERC and the Environment Agency for funding

2. Modelling Approach
Global chemistry-climate model: STOCHEM-HadAM3 (also some results from others)
Two transient runs: 1990 → 2030, following same emissions, but different climate scenarios:
1. Current Legislation (CLE)
Assumes full implementation of all current legislation
2. CLE + climate change
For 1, climate is unforced, and doesn’t change.
For 2, climate is forced by the is92a scenario, and shows a global surface warming of ~1K between 1990 and 2030.

3. STOCHEM-HadAM3 Global Lagrangian chemistry-climate model
Meteorology: HadAM3 + prescribed SSTs
GCM grid: 3.75° x 2.5° x 19 levels
CTM: 50,000 air parcels, 1 hour timestep
CTM output: 5° x 5° x 9 levels
Detailed tropospheric chemistry
CH4-CO-NOx-hydrocarbons (70 species)
includes S chemistry
Interactive lightning NOx, C5H8 from veg.
these respond to changing climate
~3 years/day on 36 processors (SGI Altix)

4. Surface O3 (ppbv) 1990s

5. BAU Change in surface O3, CLE 2020s-1990s CLE +2 to 4 ppbv over
>+10 ppbv India
+2 to 4 ppbv over
N. Atlantic/Pacific
A large fraction is
due to ship NOx
Change in surface O3, CLE 2020s-1990s
BAU

6. destruction over the oceans vegetation & changes in
ΔO3 from climate change
Warmer temperatures &
higher humidities
increase O3
destruction over the oceans
But in polluted regions, more H2O promotes O3 production; also a role from increases
in isoprene
emissions from
vegetation & changes in
lightning NOx
2020s CLEcc- 2020s CLE

7. Zonal mean ΔT (2020s-1990s)

8. Zonal mean H2O increase 2020s-1990s

9. Zonal mean change in convective updraught flux 2020s-1990s

10. C5H8 change 2020s (climate change – fixed climate)

11. Lightning NOx change 2020s (climate change – fixed climate)
HadCM3 Amazon
drying
More lightning in N mid-lats
Less, but higher, tropical convection
No overall trend in Lightning NOx
emissions

12. Zonal mean PAN decrease 2020s (climate change – fixed climate)
Colder LS
Increased
PAN
thermal
decomposition,
due to
increased T

13. Zonal mean NOx change 2020s (climate change – fixed climate)
Less
tropical
convection
and
lightning
Increased
N mid-lat
convection
and lightning
Increased
PAN
decomposition

14. Zonal mean O3 budget changes 2020s (climate change – fixed climate)

15. Zonal mean O3 decrease 2020s (climate change – fixed climate)

16. Zonal mean OH change 2020s (climate change – fixed climate)
Complex
function:
F(H2O,
NOx,
O3,
T,…)

17. Influence of climate change on O3 – 9 IPCC ACCENT models
Others dominated
by increased
stratospheric O3 influx
Influence of climate change on O3 – 9 IPCC ACCENT models
Some models dominated
By the water vapour
feedback – less O3

18. Summary
Climate change will introduce feedbacks that modify air quality
These include:
More O3 destruction from H2O (background air)
More O3 production from H2O (polluted air)
More stratospheric input of ozone
More isoprene emissions from vegetation
Changes in convection: mixing & lightning NOx
Increases in sulphate from OH and H2O2
Changes in circulation
Wetland CH4 emissions (not studied here)
Changes in stomatal uptake? (``)
These are quite poorly constrained – different models show quite a wide range of response: large uncertainties