Eric M. Leibensperger, Loretta J. Mickley, Daniel J. JacobSchool of Engineering and Applied Sciences, Harvard University

Climate response to changing United States aerosol sources: historical and projected aerosol burdens

Wei-Ting Chen, John SeinfeldDepartment of Environmental Science and Engineering, Caltech

Support from:

David StreetsArgonne National Laboratory

How do US aerosols affect climate?

GEOS-Chem chemistry transport model

GISS GCM 3 climate model

Calculation of cloud droplet number concentrations

BC, POA, SOA, (NH4)2SO4, (NH4)NO3,

Sea Salt

Aerosol indirect effect

Aero

sol d

irect

effe

ct

We are using GEOS-Chem and the model framework of Chen et al. [submitted] to conduct transient climate simulations including the aerosol direct and indirect effects.

Sensitivity simulations with GEOS-Chem and the GISS GCM allow us to quantify the impact of U.S. emissions on regional and global climate

Changes due to Indirect Effect Alone Between Pre-Industrial and Present Day[Chen et al., submitted]

GEOS-Chem Simulations

Model info:•v8-01-01 at 2°x2.5° (1yr spin-up at 4°x5°/dec)•GEOS-4 meteorology for 2001•Full Chemistry (54 tracers, RPMARES)•Historical Emissions of FF+BF SO2 and NOx from EDGAR and BC/OC from Bond [2007]•SO2, NOx, BC, and OC scale factors from David Streets following A1B•Other emissions are held constant (i.e. constant NH3, CO, etc.)

20501950 2010

Control - Reconstructed Emissions and A1B

0 U.S. SO2, NOx, and OC Emissions

0 U.S. SO2, NOx, BC, and OC Emissions

Evaluation of Present Day (2001) Emissions

Generally Underestimate Peak Values

Generally Underestimate

Well Simulated

Gradient captured, miss hot spots

Black Carbon – Bond [2007] Organic Carbon – Bond [2007]

Nitrate – EDGAR

Gradient captured, underestimate

Sulfate – EDGAR

Gradient captured, underestimated in western U.S.

Simulated well

0 0.5 1.0 1.5 μg m-3 0 1.0 2.0 3.0 μg m-3

0 1.0 2.0 4.0 μg m-33.0 0 2.25 4.50 9.00 μg m-36.75

Trends in Anthropogenic Emissions

Note: All future emissions shown above follow IPCC SRES A1B!

Trends in Tropospheric Burdens

Large biogenic/biomass sources dampen trend in OC; Nitrate increases with lessening sulfate, but still biased low; Sulfate responds to US/Europe (2000) and Asian emissions

Changes to Aerosol Optical Depth

The change in global aerosol optical depth is mainly driven by changes in sulfate, but regionally, changes to carbonaceous aerosols are important.

Global

20501950 2010

Control - Reconstructed Emissions

Constant 2010 emissions of U.S. SO2 and carbonaceous PM

0 U.S. SO2 and Carbonaceous PM

0 U.S. SO2 and Carbonaceous PM Emissions

0 U.S. SO2 and Scattering OC PM Emissions

Future Work

Eric Leibensperger – eleibens@fas.harvard.edu

Large dataset of reconstructed/projected aerosol concentrations - Additional applications?

Complete GEOS-Chem sensitivity simulations

Complete GCM Simulations with CDNC-calculated and aerosol radiative forcings

Extra Material

Large-scale changes in the gas-ratio for NH3 and total nitrate allow for less aerosol nitrate

€

Gas Ratio = NH3[ ] + NH4

+[ ] − 2 SO4

2-[ ]

HNO3[ ] + NO3−

[ ]

Formation of NH4NO3 is:

Change in Surface Nitrate

Change in Surface Sulfate

Total Aerosol Optical Depth

Will be Calculated online in GCM: External or Internal Mixing?