M ULTI -W AVELENGTH O PTICAL C ALIBRATION OF T HERMAL /O PTICAL ANALYZER AND POTENTIAL APPLICATIONS...
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MULTI-WAVELENGTH OPTICAL CALIBRATION OF THERMAL/OPTICAL ANALYZER AND POTENTIAL APPLICATIONS John G. Watson , Judith C. Chow, L.-W. Antony Chen, Xiaoliang Wang, Ben Sumlin Division of Atmospheric Sciences, Desert Research Institute, Reno, Nevada, USA
M ULTI -W AVELENGTH O PTICAL C ALIBRATION OF T HERMAL /O PTICAL ANALYZER AND POTENTIAL APPLICATIONS John G. Watson, Judith C. Chow, L.-W. Antony Chen,
M ULTI -W AVELENGTH O PTICAL C ALIBRATION OF T HERMAL /O PTICAL
ANALYZER AND POTENTIAL APPLICATIONS John G. Watson, Judith C. Chow,
L.-W. Antony Chen, Xiaoliang Wang, Ben Sumlin Division of
Atmospheric Sciences, Desert Research Institute, Reno, Nevada,
USA
Slide 2
O BJECTIVES Describe how relative values of transmittance (T)
and reflectance (R) can be related to primary calibration standards
Demonstrate the utility of additional measurements for source
apportionment Identify some of the other potential uses of
additional multiwavelength data on may samples
Slide 3
M OTIVATION Single wavelength R and T have only been used to
adjust for pyrolysis, normalized to initial R or T. It can also be
normalized to final R or T to approximate b abs. The light
source/detector combination yields different intensities within and
between instruments. More accurate b abs for several wavelengths
and detection of brown carbon requires consistency of light
intensity measurements within and among instruments Absolute
reflectance and transmittance (in %) may be used separately or
together for calculating b abs on filters, using radiative transfer
models (e.g., Beers Law, Kubelka-Munk Theory, or Monte Carlo Ray
Tracing, etc.)
Slide 4
A PPROACH 405, 445, 532, 635, 780, 808, 980 nm Perform spectral
(UV-VIS-IR) characterization of aerosol deposits throughout thermal
analysis Achieve light absorption (b abs ) measurement and
apportionment (e.g., into BC and BrC) Allow OC-EC split made by R
and T at different wavelengths 633 nm The DRI Model 2015 Carbon
Analyzer
Slide 5
T HERE ARE SEVERAL POSSIBILITIES FOR OPTICAL STANDARDS Neutral
density filters commercially available well characterized need
cutting to fit the sample holder only for transmittance do not
mimic filter optical properties Diffusive reflectance standard
commercially available only for reflectance difficult to cut for
fitting the sample holder Real-world samples need to be
characterized before deployment need to cover a wide range of R and
T need to be abundant in quantity and with reasonable
lifetimes
Slide 6
S PECTRALON D IFFUSIVE R EFLECTANCE P ANELS ARE IN COMMON USE
TO STANDARDIZE UV-VIS SPECTROMETERS
Slide 7
F ILTER TRANSFER STANDARDS WITH VARIABLE DEPOSITS CAN BE
STANDARDIZED AGAINST THESE P LATES Lambda 31 Integrating-Sphere
Spectrometer Measure R and T in two positions Filter R and T are
scaled to 0 and 100% R and T standards
Slide 8
P ROCEDURE TO QUANTIFY ABSOLUTE R AND T FOR REAL - WORLD S
AMPLES (II) I. Prepare filters and standard II. Load sample onto
cartridge III. Load samples or standard onto a holder IV. Measure
100% R standard V. Measure 0% R Standard (empty) VI. Measure filter
sample R
Slide 9
P ROCEDURE TO QUANTIFY ABSOLUTE R AND T FOR REAL - WORLD S
AMPLES (III) VII. Measure 100% T standard (empty) with closed R
port. VIII. Measure 0% T standard (blocker) with closed R port. IX.
Measure filter sample T SmolderingFlamingDiesel Road DustYellow
Sand
Slide 10
T RANSFER STANDARDS CONSIST OF DIFFERENT LOADINGS OF AN AMBIENT
OR LABORATORY - GENERATED AEROSOL #108#107#73#122#99#77#74#65
High-Vol samples acquired from the Fresno Supersite during 2003
Reflectance Transmittance 7- for carbon analysis 5/6 9/29
12/286/611/4 11/13 6/19 7/3
Slide 11
C ALIBRATION OF R AND T M EASUREMENTS BY C ARBON A NALYZER
Reflectance Transmittance Optical sensing of carbon analyzer is
calibrated with transfer standards traceable to absolute filter R
and T measurements. The uncertainty in R and T measurements by
carbon analyzer is estimated to be within 10% and much lower for
some wavelengths.
Slide 12
E XAMPLE T HERMOGRAMS Diesel Soot Sample Ambient Sample from
IMPROVE Site ROMA1 (1)Raw Data (Laser Reflectance [LR] and
Transmittance [LT] (2) After Calibration (Filter Reflectance [FR]
and Transmittance [FT])
Slide 13
S PECTRAL A BSORPTION I NFERRED FROM I NITIAL AND F INAL F
ILTER T RANSMITTANCE VARY BY SAMPLE TYPE Spectral absorption
averaged by sample type Smoldering samples acquired in DRI
combustion chamber for burning peat 4006008001200
Slide 14
S PECTRAL A BSORPTION I NFERRED FROM I NITIAL AND F INAL F
ILTER R EFLECTANCE In general, reflectance has lower S/N ratios
than transmittance R and T can be combined for better
quantification of light absorption as indicated by Petzold et al.
(2004). 4006008001200
Slide 15
D ECOUPLING BC AND B R C C ONTRIBUTIONS TO ATN Fresno Ambient
Smoldering Biomass Burning Use the Absorption Angstrm Exponent
(AAE) Model r
Slide 16
BC AND B R C C ONTRIBUTIONS TO L IGHT A BSORPTION (ATN_405 NM )
IN EACH SAMPLE * Assuming only BC absorbs at 980 nm and an AAE_BC
of 1 to extrapolate BC absorption to 405 nm. * Samples sorted by
BrC fraction (0 to 100%) in ATN_405 nm. BC dominatedBrC dominated
BC dominatedBrC dominated BC dominatedBrC dominatedr
Slide 17
IMPROVE_A EC PREDICTS ATN_BC BUT OC CORRELATES WITH ATN_B R C
ECR OCR ECT OCT Pure BrCr
Slide 18
P OTENTIAL FUTURE USES OF CALIBRATED MULTIWAVELENGTH R AND T ON
THOUSANDS OF SAMPLES More accurate measures of radiative transfer
relevant to visibility and climate Ground truth for remote
measurements from space More accurate quantification of biomass
burning and fugitive dust contributions Separation of adsorbed
organic vapors from organic carbon in aerosol deposit
Slide 19
C ONCLUSIONS Reflectance and Transmittance can be traceable to
primary standards and be made consistent among wavelengths and
instruments The detailed absorption spectrum can be approximated by
the seven wavelengths Brown carbon can be separated from black
carbon