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


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)


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)


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)


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)


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)


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)


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)


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)


Model O3 too low in boundary layerin summer - autumn

Resolute (75N, 95W), Canada

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


Surface O3 generally too high

Mid-troposphere in summer too low

Sapporo (43N, 141E), Japan

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


Mid- & upper-troposphericO3 too low in summer

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

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


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)


  • 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 but is far from perfect.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


1990s but is far from perfect.

Decadal mean values


BAU 2020s but is far from perfect.


+2 to 4 ppbv over but is far from perfect.

N. Atlantic/Pacific

>+10 ppbvIndia

A large fraction is

due to ship NOx

Change in surface O3, BAU 2020s-1990s

BAU


MRF 2020s but is far from perfect.


Up to -10 ppbv but is far from perfect.over continents

Change in surface O3, MRF 2020s-1990s

MRF

BAU


BAU+climate change 2020s but is far from perfect.


Look at the difference between these but is far from perfect.

two to see influence of climate change

Change in surface O3, BAUcc 2020s-1990s

MRF

BAU

BAU+cc


O 3 from climate change
Δ but is far from perfect.O3 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 but is far from perfect.O3 & ΔO3 (2020s-1990s)

BAU ΔO3

1990s

MRF ΔO3

BAUcc ΔO3


Zonal mean oh oh 2020s 1990s
Zonal mean OH but is far from perfect. & ΔOH(2020s-1990s)

BAU ΔOH

1990s

MRF ΔOH

BAUcc ΔOH


CH but is far from perfect.4, CH4 & OH trajectories 1990-2030

Current CH4 trend

looks like MRF –

coincidence?

All scenarios show increasing OH


Conclusions
Conclusions but is far from perfect.

  • 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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