2020 vision modelling the near future tropospheric composition
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2020 vision: Modelling the near future tropospheric composition. David Stevenson Institute of Atmospheric and Environmental Science School of GeoSciences The University of Edinburgh Thanks to: Ruth Doherty (Univ. Edinburgh) Dick Derwent (rdscientific)

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2020 vision modelling the near future tropospheric composition

2020 vision:Modelling the near future tropospheric composition

David Stevenson

Institute of Atmospheric and Environmental ScienceSchool of GeoSciencesThe University of Edinburgh

Thanks to:

Ruth Doherty (Univ. Edinburgh)

Dick Derwent (rdscientific)

Mike Sanderson, Colin Johnson, Bill Collins (Met Office)

Frank Dentener (JRC Ispra), Markus Amann (IIASA)

talk structure
Talk Structure
  • Chemistry-climate model: STOCHEM-UM
  • Several transient runs: 1990 → 2030
  • the 1990s
    • how modellers use observations
      • comparisons with ozone-sonde data
  • the 2020s
    • what is needed to predict the future?
      • a believable model (hence the first bit)
      • a computationally efficient model
      • future emissions
      • climate change
      • other things?
  • What are the results telling us?
stochem
STOCHEM
  • Global Lagrangian 3-D 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
    • detailed oxidant photochemistry
  • Interactive lightning NOx, C5H8 from veg.
  • ~1 year/day on 36 processors (Cray T3E)
model experiments
Model experiments
  • Several transient runs: 1990 → 2030
  • Driving meteorology
    • Fixed SSTs (mean of 1978-1996)
    • SSTs from a climate change scenario (is92a)
      • shows ~1K surface warming 1990s-2020s
    • Shorter run with observed SSTs 1990-2002
  • New IIASA* global emissions scenarios:
    • Business as usual (BAU)
    • Maximum reductions feasible (MRF)
  • Stratospheric O3 is a fixed climatology
  • Vegetation (land-use) also a fixed climatology

*IIASA: International Institute for Applied Systems Analysis (Austria)

iiasa emissions scenarios
IIASA Emissions scenarios

Global totals – there are significant regional variations

Courtesy of Markus Amann (IIASA) & Frank Dentener (JRC)

model experiments1

Compare with 1990s obs

Model experiments

BAU, observed SSTs 1990-2002

BAU, fixed SSTs 1990-2030

MRF, fixed SSTs 1990-2030

BAU, is92a SSTs 1990-2030

2030

1990

slide7

Chemical tropopause (O3=150 ppbv)

Hohenpeissenberg Ozone-sonde model vs observations

(monthly data for the 1990s)

Ozone-sonde data from Logan et al. (1999 - JGR)

slide8

Chemical tropopause (O3=150 ppbv)

Hohenpeissenberg Ozone-sonde model vs observations

(monthly data for the 1990s)

Ozone-sonde data from Logan et al. (1999 - JGR)

slide9

Chemical tropopause (O3=150 ppbv)

Hohenpeissenberg Ozone-sonde model vs observations

(monthly data for the 1990s)

Model> obs

Model< obs

Ozone-sonde data from Logan et al. (1999 - JGR)

slide10

Chemical tropopause (O3=150 ppbv)

±1 std dev in obs

Hohenpeissenberg Ozone-sonde model vs observations

(monthly data for the 1990s)

Ozone-sonde data from Logan et al. (1999 - JGR)

slide11

Chemical tropopause (O3=150 ppbv)

±1 std dev in obs

±1 std dev in model

Hohenpeissenberg Ozone-sonde model vs observations

(monthly data for the 1990s)

Ozone-sonde data from Logan et al. (1999 - JGR)

slide12

Chemical tropopause (O3=150 ppbv)

Hohenpeissenberg Ozone-sonde model vs observations

(monthly data for the 1990s)

Model overestimatesby >1 std dev

Model underestimatesby >1 std dev

Ozone-sonde data from Logan et al. (1999 - JGR)

slide13

Chemical tropopause (O3=150 ppbv)

Hohenpeissenberg Ozone-sonde model vs observations

(monthly data for the 1990s)

Model overestimatesby >1 std dev

Identify where andwhen the model iswrong

Model underestimatesby >1 std dev

Ozone-sonde data from Logan et al. (1999 - JGR)

slide14

Model O3 too low in lower tropospherefor all seasons except spring

Ny Alesund (79N, 12E), Spitzbergen

Ozone-sonde data from Logan et al. (1999 - JGR)

slide15

Model O3 too low in boundary layerin summer - autumn

Resolute (75N, 95W), Canada

Ozone-sonde data from Logan et al. (1999 - JGR)

slide16

Surface O3 generally too high

Mid-troposphere in summer too low

Sapporo (43N, 141E), Japan

Ozone-sonde data from Logan et al. (1999 - JGR)

slide17

Mid- & upper-troposphericO3 too low in summer

Wallops Island (38N, 76W), Eastern USA

Ozone-sonde data from Logan et al. (1999 - JGR)

slide18

Major O3 underestimate intropical mid-troposphere –too much destruction?or not enough sources?

OK at surface, but…

Ascension (8S, 14W), Mid-Atlantic

Ozone-sonde data from Thompson et al. (2003 - JGR)

slide19
The model has some skill at simulating tropospheric ozone, but is far from perfect.
  • Careful comparisons with other gases (NOx, NOy, etc.) also needed, but there is much less data.
  • For climate-chemistry model validation, lengthy climatologies, including vertical profiles are most useful.
  • If you want modellers to uses the data, provide it in easy-to-use formats (we’re lazy!)
  • MOZAIC (operational aircraft data) and satellite data are examples of the sort of datasets needed.
  • If you trust the model, it may be useful for future predictions…
model experiments2

Compare with 1990s obs

Compare changes betweenthe 1990s and 2020s

Model experiments

BAU, observed SSTs 1990-2002

BAU, fixed SSTs 1990-2030

MRF, fixed SSTs 1990-2030

BAU, is92a SSTs 1990-2030

2030

1990

slide21

1990s

Decadal mean values

slide23

+2 to 4 ppbv over

N. Atlantic/Pacific

>+10 ppbvIndia

A large fraction is

due to ship NOx

Change in surface O3, BAU 2020s-1990s

BAU

slide25

Up to -10 ppbvover continents

Change in surface O3, MRF 2020s-1990s

MRF

BAU

slide27

Look at the difference between these

two to see influence of climate change

Change in surface O3, BAUcc 2020s-1990s

MRF

BAU

BAU+cc

o 3 from climate change
ΔO3 from climate change

Warmertemperatures &

higher humidities

increase O3

destruction over the oceans

But also a role

from increases

in isoprene

emissions from

vegetation?

zonal mean o 3 o 3 2020s 1990s
Zonal mean O3 & ΔO3 (2020s-1990s)

BAU ΔO3

1990s

MRF ΔO3

BAUcc ΔO3

zonal mean oh oh 2020s 1990s
Zonal mean OH & ΔOH(2020s-1990s)

BAU ΔOH

1990s

MRF ΔOH

BAUcc ΔOH

slide31

CH4, CH4 & OH trajectories 1990-2030

Current CH4 trend

looks like MRF –

coincidence?

All scenarios show increasing OH

conclusions
Conclusions
  • Model development and validation is ongoing, & is guided by observations
  • Anthropogenic emissions will be the main determinant of future tropospheric O3
    • Ship NOx looks important
  • Climate change will introduce feedbacks that modify air quality
  • We can estimate the radiative forcing implications of air quality control measures
  • NB: Many processes still missing
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