Quantitative Interpretation of Satellite and Surface Measurements of Aerosols over

North America

Aaron van Donkelaar

M.Sc. Defense

December, 2005

Aerosols – Why do we care?

• Climate Change– Direct Effect– Indirect Effect

• Health Effects (PM2.5)– Lung cancers– Pulmonary Inflammation

• Visibility

Image from http://cariari.ucr.ac.cr/~faccienc/temas2/planeta.htm

Part I – Remote Sensing of Ground-Level PM2.5

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Column Mass Loading:

Ground-Level PM2.5:

• ρ – particle mass density• r – effective radius• τ – aerosol optical depth

• Qe – Mie extinction efficiency

• z – Height of regional air mass

subscript d denotes dry conditions

InstrumentationMODIS• Moderate Resolution Imaging

Spectroradiometer• 32 channels (7 used for

Aerosol Retrieval): 0.47, 0.55, 0.67, 0.87, 1.24, 1.64 um

• Approx. daily global coverage• Requires dark surface for AOD

retrieval

MISR• Multiangle Imaging

Spectroradiometer• 4 spectral bands at 9 different

viewing angles• 6-9 days for global coverage• No assumption regarding

surface reflectivity

GEOS-CHEM

• 50 Tracers• 1º x 1º resolution• 30 vertical levels (lowest at ~10, 50, 100, 200, 300 m)• GMAO fields: temperature, winds, cloud properties, heat flux and

precipitation• sulphate, nitrate, mineral dust, fine/coarse seasalt, organic and black

carbon• Aerosol and oxidant simulations

coupled through– formation of sulphate and nitrate

– heterogeneous chemistry

– aerosol effect of photolysis rates

• Seasonal average biomass burning

Remote vs. Ground PM2.5

MODIS MISR

standard 0.68 0.54

constant vertical structure (τz/τ) 0.29 0.29

constant AOD 0.54 0.38

constant aerosol properties (Qe, r, rd, ρd)

0.73 0.52

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Scatter Plot Comparison/Table Holding Constants

Temporal Correlation

Glo

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Part II –Organic Aerosol Sources

• Primary Sources:– combustion (biomass/biofuel)

• Secondary Sources:– condensation of gaseous species– not well understood

• GEOS-CHEM OA Simulation– Seasonally varying biomass burning inventories– Inversion removed– SOA based upon Chung and Seinfeld [2002]

• Biogenic emissions from MEGAN inventory

• HxCy + (O3, OH, NO3) → semi-volatile products

IMPROVE Organic Aerosol

IMPROVE – GEOS-CHEM Organic Aerosol

Isoprene conversion fits within model biases

Large effect from non-OA condensation

Conclusions

• Remote PM2.5

– significant correlation (MODIS: R=0.68, MISR:0.54)– dominant factors include AOD and vertical structure

– reveals global regions of high PM2.5

• Sources of Organic Aerosol– isoprene conversion reduces model bias– non-OA condensation unclear