Task 221

Optical Properties Of Mineral Dust Aerosol

Principal Investigator(s):

R. Hansell

Sponsor(s):

S. Tsay

Last Updated:

October 26, 2012 15:25:48

Description of Problem

To investigate the optical properties of mineral dust aerosol between the near to thermal IR using global aerosol field measurements combined with analysis of model data to help advance ground and satellite-based remote sensing applications and column energetic studies.

Scientific Objectives and Approach

Specific objectives were:

• Applying spherical and non-spherical light scattering codes to calculate dust aerosol mass extinction and absorption efficiencies (MEE and MAE, respectively) at wavelengths commonly used in remote sensing, covering an extended range of dust physicochemical properties including particle chemistry, morphology, and size.

• Provides reference to facilitate interpreting field measurements of dust aerosol

• Identify spectral relationships in dust MEE values between the near and thermal IR useful for estimating thermal impacts on retrieved parameters such as SST and for identifying long wave radiative effects of dust aerosol.

• Provides constraint for modeling studies

• Utilizing hyperspectral radiance measurements from NASA Goddard’s ground-based Atmospheric Emitted Radiance Interferometer (AERI) to probe the longwave radiative impacts of dust aerosol near major source regions.

• Evaluate/compare direct aerosol radiative effects (DARE) of global dust over the column atmosphere

• Develop satellite-based methodology for retrieving dust properties in the IR with focus on nighttime dust applications

Accomplishments

• Successfully completed a detailed modeling study of the optical properties of dust aerosol between the near and thermal IR wavelengths which provides an envelope of expected MEE values corresponding to extreme cases in dust physicochemical properties.

• Completed study of DARE over Cape Verde Islands during the NAMMA field experiment (2006) using NASA Goddard’s ground-based facilities (SMART-COMMIT)

• Completing study of DARE for dust aerosol during the Asian Monsoon Year (2008) field campaign using NASA Goddard’s ground-based facilities (SMART-COMMIT) in Zhangye China (manuscript in preparation).

• Results will later be compared with other global regions including the NAMMA study to evaluate differences/similarities in the radiative energetics.

• Conducting sensitivity tests to identify impacts of water vapor, temperature, and emissivity on measuring dust signals using MODIS thermal IR channels.

Refereed Journal Publications

Hansell, R., J.S. Reid, S.C. Tsay, T.L. Roush, and O. V. Kalashnikova, A Sensitivity Study on the Effects of Particle Chemistry, Asphericity and Size on the Mass Extinction Efficiency of Airborne Mineral Dust in the Thermal IR, Atmos. Chem. Phys., 2011 – Accepted

Hansell, R., J.S. Reid, S.C. Tsay, T.L. Roush, and O. V. Kalashnikova, A Sensitivity Study on the Effects of Particle Chemistry, Asphericity and Size on the Mass Extinction Efficiency of Airborne Mineral Dust in the Thermal IR, Atmos. Chem. Phys. Discuss,10, 17213-17262, 2010a.

Hansell, R., S.C. Tsay, Q. Ji, N.C. Hsu, M.J. Jeong, S.H. Wang, J.S. Reid, K.N. Liou, and S.C. Ou, An Assessment of the Surface Longwave Direct Radiative Effect of Airborne Saharan Dust during the NAMMA Field Campaign, J. Atmos Sci. NAMMA special issue, 67, 1048-1065, doi:10.1175/2009JAS3257.1, 2010b.

Task Figures

Fig. 1 – Calculated MEE of dust aerosol from the near to thermal IR over extended ranges of particle shape, size and composition. The values shown represent the maximum MEE for each channel investigated. Note the two dominant peaks at the near and thermal IR wavelengths, both associated with non-spherical particles.

Fig. 2 – (a) airborne dust at Sal Island, Cape Verde during the NAMMA field campaign (2006) as observed by NASA Goddard’s AERI instrument. (b) Surface longwave DARE (or direct radiative effect – DRE) plotted versus AERI retrieved AOT.