Aerosol optical properties include spectrally- and angularly-resolved scattering, absorption and extinction coefficients, which yield single-scattering albedos, angstrom exponents, and phase function. These parameters are needed for:

 

• Validating remote sensor optical depths and retrievals of aerosol extensive properties
• Investigating sub-pixel variability in satellite optical depth data products
• Providing a link between in situ and remote sensor observations
• Establishing the characteristics of aerosol sources (e.g., biomass burning, automobile combustion, dust, sea-salt, etc.)
• Apportioning column-based aerosol optical depth observations to different particle sources/types

 

LARGE uses the following instruments to measure key optical properties.

 

Absorption Coefficients

•        Particle Soot Absorption Photometer (PSAP, Radiance Research)

o   Filter-based measurements at 470, 535 and 660 nm

o   Single sample and reference filters

o   Corrected for filter scattering using empirical procedures

o   Sensitivity < 1 Mm^-1

o   Sealed filter compartment, suitable for low-pressure operation

o   Flown on NASA aircraft in atmospheric composition studies since 1996

o   http://www.esrl.noaa.gov/gmd/aero/instrumentation/psap_desc.html

 

•        Tri-color Absorption Photometer (TAP, Brechtel Manufacturing, Inc.)

o   New instrument based on NOAA's Continuous Light Absorption Photometer (CLAP)

o   Operates similarly to PSAP, but has multiple sample and reference filter spots, advances automatically when filter transmission drops below threshold

o   Wavelengths and performance characteristics similar to PSAP

o   Sealed filter compartment, suitable for aircraft deployment

o   http://www.brechtel.com/products-item/tricolor-absorption-photometer/

 

•        Three-Wavelength Photo-acoustic Aerosol Soot Spectrometer (PASS-3, DMT)

o   405, 532 and 781 nm wavelengths

o   Sensitivity of ~5 Mm^-1/sec for 781 nm channel, less for 405 and 532.

o   Susceptible to background noise and sample pressure fluctuations

o   Used primarily for lab studies and combustion source characterization

o   See: http://www.dropletmeasurement.com/products/airborne/PASS-3

 

•        Multi-angle Aerosol Absorption Photometer (MAAP, Thermo-Scientific)

o   Reel-to-reel filter instrument similar to Magee Scientific Aethalometer

o   Red wavelength, 0.1 Mm^-1 sensitivity for 2-minute average

o   Continuous measurement of black carbon and aerosol light absorption properties

o   Multiple detectors to simultaneously measure transmitted and scattered light

o   Transmission corrected for scattering using radiation-transfer algorithm

o   Filter does not seal, not suitable for use on aircraft

o   Used extensively in characterizing black-carbon emissions from aircraft

o   http://www.thermoscientific.com/content/tfs/en/product/5012-multiangle-absorption-photometer-maap.html

 

•        7-wavelength Aethalometer (AE-33, Magee Scientific)

o   Reel-to-reel filter-based instrument

o   Measurements at 370, 470, 520, 590, 660, 880 and 950 nm

o   Provides insight into brown-carbon absorption

o   Coefficients not corrected for filter scattering

o   Not suitable for low pressure operation, best for monitoring trends at ground stations

o   http://www.mageesci.com/images/stories/docs/aethalometer_ae33_specifications.pdf

 

•        Liquid Waveguide Aerosol Absorption Spectrometer (under development at LaRC)

o   Based on approach pioneered by Rodney Weber at Georgia Tech

o   Particle-into-liquid-sampler (PILS) connected to a 1-m waveguide with a broad-band light source and spectrometer on each end

o   Wavelength range 350-700 nm

o   Includes 3 channels to measure background and buffer absorption

o   Designed for ground-based and airborne operation

o   http://www.atmos-chem-phys.net/10/5965/2010/acp-10-5965-2010.pdf

 

•        Differential Photo-acoustic Absorption Photometer (ARI, Phase-II NASA SBIR project)

o   Single-wavelength

o   Designed for black-carbon measurements in combustion studies

o   Project to be completed by 2017

 

Scattering Coefficients

•        3-Wavelength Integrating Nephelometer (TSINeph, TSI 3563)

o   Sensitive from 7 to 170 deg scattering angle; corrections applied for truncation errors

o   Detects total- and hemispheric back-scattering at 450, 550, and 700 nm

o   Precision of ~0.5 Mm^-1 for 1 second average

o   Temporal response 1 sec

o   Works well at low pressure

o   Deployed on NASA aircraft for inflight measurements dozens of missions since 1996

o   Used in combination with sample humidifier to measure f(RH)

o   http://www.tsi.com/integrating-nephelometer-3563/

 

•        Single-Wavelength Nephelometer (RRNeph, Radiance Research M903)

o   Small unit suitable for ground and airborne applications

o   Detects scattering at 535 nm

o   Precision of ~0.5 Mm^-1 for 5 second average

o   Not as stable as TSI units, thus mainly used for ground applications

o   http://www.esrl.noaa.gov/gmd/aero/instrumentation/RR_neph.html

 

•        3-Wavelength Integrating Nephelometer (APNeph, Air Photon, Inc)

o   Angular sensitivity from 7 to 170 deg

o   Detects total- and hemispheric scattering at 450, 532 and 632 nm

o   Suitable for use on ground and airborne platforms

o   Stated precision of 0.1 Mm^-1 for longer averaging times

o   http://www.airphoton.com/nephelometers/

 

•        Polarized Imaging Nephelometer (PINeph, provided by collaborator Vanderlei Martins, UMBC)

o   Measures aerosol phase function inside a closed chamber

o   Sensitivity down to Rayleigh scattering

o   Angular coverage from 1.5 to 178.5degs, with 0.5degs resolution

o   Included in LARGE instrument suite on DC3, SEAC4RS and DISCOVER-AQ

o   http://userpages.umbc.edu/~martins/laco/projects.htm

 

Extinction Coefficients

•        Cavity-Attenuated Phase-Shift Particle Extinction Monitor (CAPS PMex, Aerodyne)

o   Three separate units provide total extinction at 450, 530 and 630 nm

o   Precision of < 2 Mm^-1 for 1 second average

o   Suitable for ground and airborne applications

o   Deployed on NASA Falcon during ACCESS II; used in a number of ground-based studies

o   NASA SBIR-funded project seeks to combine all three wavelengths in a single box

o   http://www.aerodyne.com/products/caps-pmex-monitor

 

•        Spectral Aerosol Extinction Monitor (SpEx, developed by Carolyn Jordan, NIA/LARGE)

o   Long-path (39 m) extinction cell with fiber-optic couplings to broad-band source and spectrometer

o   Wavelength-range from 300 to 700 nm, with <1 nm resolution

o   Designed to provide information on brown-carbon absorption

o   Detection limit <20 Mm^-1 for single scans

o   Successfully deployed onboard LARGE MACH-2 mobile laboratory during DISCOVER-AQ Colorado to measure spectral extinction from a variety of sources

o   Used in lab to characterize optical properties of aerosol and dust particles

o   Ongoing work by Dr. Jordan focuses on improving instrument precision and immunity to vibration and noise

o   For similar instrument see--http://scholars.unh.edu/chemistry_facpub/6/