In Situ and Remote Sensing Characterization of Spectral Absorption by Black Carbon and other Aerosols J. Vanderlei Martins, Paulo Artaxo, Yoram Kaufman, Shana Mattoo, MODIS Aerosol group, AERONET, and University of Sao Paulo Air Pollution Group In situ Aerosol Absorption (absorption Efficency m2/g) Remote Sensing of Aerosol Absorption –Over land (will not be presented here) –Over the ocean sunglint

In Situ Measurements of Aerosol Absorption Simple strategy for Remote Sensing and in Situ: Particles Reflectance over bright surfaces Particles collected on filter’s surface Particles in suspension in the atmosphere Has already been used for a long time… But we have a new semi-empirical model and good calibration!!!

Types of Particles Saharan Dust Smoke Cluster Smoke Smoldering Phase Smoke Flaming Phase US Urban Pollution

BC Absorption Efficiency curve using Mie Theory abs. coef. (m2 g-1) volume distribution diameter (um) absorp. coef.volume distribution Estimated absorption coeficient for the BC standard using Mie theory Calculated  aBC = 6.8 m2/g

Semi-Empirical Calibration: Measured 6.8m 2 /g

Size Distributions - AERONET São Paulo México Santiago Fine Mode – Dp <2.5  m AVG mass density 0.10g/m 2 Coarse Mode < Dp < 10  m AVG mass density 0.34g/m 2 Sao Paulo – Aerosol Absorption Efficiency Small Absorbers: 1/ spectral dependence Coarse Fine

Resuspended Particles from Santiago del Chile: very large dust + urban pollution particles Aerosol Mass Absorption Efficiency

Derivation of the single scattering albedo of dust from MODIS spectral measurementsThe spectral single scattering albedo is 0.94 in the blue (0.47 µm), 0.97 in the green (0.55 µm), in the red (0.66 µm) and 1.00 for longer wavelengths. Kaufman et al.,GRL 2002

Dust Absorption Effect Saharan Dust US Urban Pollution Results can be combined with elemental composition from the same filter… There is capability to distinguish Dust from BC absorption Dust BC absorption

Dust Absorption Effect Saharan Dust US Urban Pollution Dust BC absorption

Pollution from developing countries is highly absorbing!!!

Biomass Burning

But Not Only Smoke and Dust Absorbs Light…

Biomass Burning aerosols from the Amazon – SMOCC 2002

Aerosol Absorption over sunglint Solar glint over Lago Maggiore, Italy, June 27, The haze is a regional, heavy pollution (optical thickness~1) in addition to dust from the Sahara [Gobbi et al., 2000]. Dust absorbs more in the blue than in the red part of the spectrum, giving the glint its golden color. A hypothetical spaceborne Instrument to Measure Aerosol Absorption using the Glint, IMAG, is using two planes of observation: one through the glint and one 40° off-glint. The arrow shows the direction of the spacecraft movement. The off glint aerosol measurements against the dark ocean are used to determine the aerosol scattering properties. The glint measurements, 1 minute apart, are used to derive the aerosol absorption over the bright glint. Accurate radiance measurements (taking into account the polarized light) Good agreement between Surface Spectral Model and Measurements: Empirical calibration/adjustments in aerosol clean cases – Same for AEROSAT High Accuracy retrievals of aerosol Scattering properties: AOT, size and Refractive index.

Aerosol absorption over sunglint– Kaufman et al GRL Use the spectral measurements over the glint to derive the aerosol absorption optical thickness associated with the presence of black carbon. Correlated with Earth Radiation Budget measurements these measurements can be used to determine the black carbon aerosol forcing of climate. Aerosol effect on sun-glint reflectance is weakly dependent on aerosol effective radius and refractive index but strongly dependent on the absorption and scattering optical thickness Varying effective radius and refractive index Varying Absorption Optical Thickness

Aerosol Absorption over sunglint MODIS: Spectral measurements over the Sunglint AERONET: High Accuracy retrievals of aerosol Scattering properties: AOT, size and Refractive index. MODIS + AERONET: 1 – Invert Downward radiances from AERONET using MODIS LUT 2 – Adjust LUT effective Wind speed based on 2.1  m channel 3 – Use selected models (size, type, and AOT) to fit MODIS upward radiances to LUT over the glint

 o retrievals with MODIS over sunglint at COVE Wavelength (um) oo oo

 o retrievals with MODIS over sunglint at Male

Conclusions In situ spectral reflectance in filters provides a simple and accurate measurement of absorption efficiency (m 2 /g) and abs. coefficient (m -1 ) Remote sensing of Aerosol Absorption is possible over the ocean sunglint and present good accuracy and sensitivity