Future Inorganic Aerosol Levels

4th GEOS-Chem Users’ Meeting9 April 2009

Future Inorganic Aerosol Levels

4th GEOS-Chem Users’ Meeting9 April 2009

Havala Pye*1, Hong Liao2, Shiliang Wu3,5, Loretta Mickley3, Daniel Jacob3, Daven Henze4,6, John

Seinfeld1

1California Institute of Technology, 2Chinese Academy of Sciences,

3Harvard University, 4Columbia University

5 now at Michigan Technological University6 now at University of Colorado at Boulder

Havala Pye*1, Hong Liao2, Shiliang Wu3,5, Loretta Mickley3, Daniel Jacob3, Daven Henze4,6, John

Seinfeld1

1California Institute of Technology, 2Chinese Academy of Sciences,

3Harvard University, 4Columbia University

5 now at Michigan Technological University6 now at University of Colorado at Boulder

Determine the effect of climate and emissions changes on future sulfate-nitrate-ammonium (SNA) aerosols with a focus on surface concentrations in the U.S.

Objective

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GISS GCM meteorology(year 2000 or 2050)

Anthropogenic emissions(year 2000 or 2050)

GEOS-Chem with ISORROPIA II

sulfatenitrate

ammonium

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Inorganic AerosolsFrom Gas Phase Precursors

DMS gas phase chemistry

SO2 Chemistry

SO42-

Aerosol Phase in Thermodynamic Equilibrium: ISORROPIA II

DMS emission

SO4 emission

SO2 emission

NH4+

water

NH3

NH3 emission

NO3-

HNO3

Na+ Cl-Ca2+

Mg2+K+

NOX chemistry

NOX emission

Sea salt emission

Simulated Present-dayNitrate Concentrations

[µg/m3]

DJF MAM

JJA SON

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Nitrate Predictions Compared to Observations

Sim

ula

ted [

µg/m

3]

Measured [µg/m3]

Sim

ula

ted [

µg/m

3]

Measured [µg/m3]

DJF MAM

JJA SON

• Agreement with observations improved compared to previous ISORROPIA

• Sensitivity tests performed for conditions representative of JJA in So. California

– Predictions not very sensitive to total ammonia available

– Possible model limitation at low RH

Predicted Change in total SNA due to Changes in Climate Alone

(anthropogenic emissions at present-day levels)

Multiple changes potentially important for aerosols including changes in:

• Windspeed/transport• Oxidant levels (sulfate)• Precipitation

• Frequency of mid-latitude cyclones [Wu et al., 2008]

• Temperature (nitrate)• Dry deposition (nitric acid)

• Humidity

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Future climate:• year 2050 (GHG follow IPCC

A1B) from GISS GCM III [Wu et al., 2008]

• 522 ppm CO2

• 1.6 K global mean surface temperature rise

• 8% increase in global annual mean precipitation

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Future Anthropogenic Emissions

Based on IPCC A1B scenario for 2050

NH3 NOX SO2 SO4

40%

-35%

-74% -75%

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Predicted Change due to Changes in Anthropogenic Emissions

(climate at present-day conditions)

SO4-2 NO3

– NH4+

Annual SNA levels decrease due to

• Lower sulfate levels as a result of lower SO2 emissions

• Generally lower ammonium as a result of lower sulfate levels

DJF SNA levels increase on the order of 1 g/m3 due to

• Increased nitrate aerosol levels as a result of more ammonia and lower sulfate concentrations

Climate Change with Constant Emissions

• Sulfate more important for determining trend with present-day emissions

• Nitrate more important for determining trend with future emissions

Present-day Emissions{(2050 Climate, 2000 Emissions) - (2000 Climate, 2000 Emissions)}

Future Anthropogenic Emissions{(2050 Climate, 2050 Emissions) - (2000 Climate, 2050 Emissions)}

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Conclusions

• Climate change alone is predicted to lead to improvements in air quality in the SE U.S. but degraded air quality in the MW and NE– Sulfate increases in the MW and NE– Nitrate generally decreases

• Predicted changes in SNA levels in the U.S. are more strongly influenced by changes in emissions than changes in climate (for the scenario considered here)– SNA levels are generally predicted to be lower due to domestic SO2

emission reductions– Nitrate levels are generally predicted to be higher due to increased NH3

emissions and lower sulfate despite decreasing NOX emissions

• The response of SNA aerosols to climate change depends on the anthropogenic emissions for the MW and NE

For more information see: Pye et al. J. Geophys. Res. 2009

Acknowledgements

This work was supported by the U.S. Environmental Protection Agency’s STAR Program (grants RD830959 and RD833370). Havala Pye was supported by a NSF Graduate Research Fellowship. Hong Liao acknowledges support from the National Natural Science Foundation of China (grant 40775083). Discussions with Becky Alexander and Athanasios Nenes are greatly appreciated.