MULTI-WAVELENGTH OPTICAL CALIBRATION OF THERMAL/OPTICAL ANALYZER AND

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1 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

2 OBJECTIVES 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

3 MOTIVATION 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., Beer s Law, Kubelka-Munk Theory, or Monte Carlo Ray Tracing, etc.)

4 APPROACH 633 nm 45, 445, 532, 635, 78, 88, 98 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 The DRI Model 25 Carbon Analyzer

5 THERE 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

6 SPECTRALON DIFFUSIVE REFLECTANCE PANELS ARE IN COMMON USE TO STANDARDIZE UV-VIS SPECTROMETERS

7 FILTER TRANSFER STANDARDS WITH VARIABLE DEPOSITS CAN BE STANDARDIZED AGAINST THESE PLATES Lambda 3 Integrating-Sphere Spectrometer Measure R and T in two positions Filter R and T are scaled to and % R and T standards

8 PROCEDURE TO QUANTIFY ABSOLUTE R AND T FOR REAL-WORLD SAMPLES (II) I. Prepare filters and standard II. Load sample onto cartridge III. Load samples or standard onto a holder IV. Measure % R standard V. Measure % R Standard (empty) VI. Measure filter sample R

9 PROCEDURE TO QUANTIFY ABSOLUTE R AND T FOR REAL-WORLD SAMPLES (III) VII. Measure % T standard (empty) with closed R port. VIII. Measure % T standard (blocker) with closed R port. IX. Measure filter sample T Smoldering Flaming Diesel Diesel Road Dust Yellow Sand Reflectance (%) Flaming Smoldering Mobile Mobile Road Dust Yellow Soil "Teflon" Wavelength (nm) Transmittance (%) Flaming Smoldering 3 Mobile 2 Mobile Road Dust Yellow Soil "Teflon" Wavelength (nm)

10 TRANSFER STANDARDS CONSIST OF DIFFERENT LOADINGS OF AN AMBIENT OR LABORATORY- GENERATED AEROSOL 5/6 6/9 7/3 9/29 2/28 6/6 /4 /3 #65 #74 #77 #99 #22 #73 #7 #8 High-Vol samples acquired from the Fresno Supersite during 23 Reflectance (%) 8 7 FSH65 %R FSH74 %R 6 FSH77 %R 5 FSH99 %R 4 FSH22 %R 3 FSH73 %R FSH7 %R 2 FSH8 %R Wavelength (nm) Reflectance Transmittance (%) FSH65 %T FSH74 %T FSH77 %T FSH99 %T FSH22 %T FSH73 %T FSH7 %T FSH8 %T Wavelength (nm) Transmittance 7-λ for carbon analysis

11 CALIBRATION OF R AND T MEASUREMENTS BY CARBON ANALYZER Reflectance Filter Reflectance (FR by Lambda 35) Linear 45 nm; (45 r 2 nm) =.99 Linear 445 nm; (455 r 2 nm) =.99 Linear 532 nm; (532 r 2 nm) =.92 Linear 635 nm; (635 r 2 nm) =.97 Filter Reflectance (FR by Lambda 35) Linear 78 nm; (78 r 2 = nm).99 Linear 88 nm; (88 r 2 = nm).99 Linear 98 nm; (98 r 2 = nm).99 Linear 633 nm (TOA633nm) * ;r 2 = Laser Reflectance (LR in mv, by Retrofit) Laser Reflectance (LR in mv, by Retrofit).2.2 Transmittance Filter Transmittance (FT by Lambda 35). Linear 532 nm; (532 r 2 nm) =.99 Linear 635 nm; (635 r 2 nm) =.99 Linear 98 nm; (98 r 2 nm) =.99 Linear 633 (TOA633nm) * ;r 2 =.99 Filter Transmittance (FT by Lambda 35). Linear 45 nm; (45 r 2 nm) =.99 Linear 445 nm; (455 r 2 nm) =.99 Linear 78 nm; (78 r 2 nm) =.99 Linear 88 nm; (88 r 2 nm) = Laser Transmittance (LT in mv, by Model 2) Laser Transmittance (LT in mv, by Model 2) 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 ±% and much lower for some wavelengths.

12 Temp 8 LR LT 3 Carbon Temp. 5 FT 4 3 Carbon Carbon 5 Analysis Time (sec) 9. 4 FR 7 5 Analysis Time (sec) Ambient Sample from IMPROVE Site ROMA Filter Reflectance & Transmittance (FR & FT) 8 LT Temperature ( C) & Carbon (ng/cm2) Filter Reflectance & Transmittance (FR & FT) (2) After Calibration (Filter Reflectance [FR] and Transmittance [FT]) Temp 6 Analysis Time (sec) LR Temp FR. 6 5 FT. 4 3 Carbon Analysis Time (sec) Diesel Soot Sample 5 Temperature ( C) & Carbon (ng/cm2) Laser Reflectance & Transmittance (LR & LT in raw counts) Temperature ( C) & Carbon (ng/cm2) () Raw Data (Laser Reflectance [LR] and Transmittance [LT] Laser Reflectance & Transmittance (LR & LT in raw counts) Temperature ( C) & Carbon (ng/cm2 ) EXAMPLE THERMOGRAMS

13 SPECTRAL ABSORPTION INFERRED FROM INITIAL AND FINAL FILTER TRANSMITTANCE VARY BY SAMPLE TYPE Spectral absorption averaged by sample type Smoldering samples acquired in DRI combustion chamber for burning peat

14 SPECTRAL ABSORPTION INFERRED FROM INITIAL AND FINAL FILTER REFLECTANCE ARN ln,, ) 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. (24).

15 DECOUPLING BC AND BRC r CONTRIBUTIONS TO ATN.6.6 τ a, y = x R² = Measured BC Fraction τ a, y = 5E+2x 4.89 R² = Measured BC Fraction.6.4 y = 2E+x 4.44 R² = y = x R² = Wavelength λ (nm) Wavelength λ (nm) Fresno Ambient Smoldering Biomass Burning Use the Absorption Angström Exponent (AAE) Model ATN ATN λ

16 BC AND BRC r CONTRIBUTIONS TO LIGHT ABSORPTION (ATN_45NM) IN EACH SAMPLE ATN_45nm_BC ATN_45nm_BrC Fresno Supersite BrC dominated BC dominated IMPROVE ATN_45nm_BC ATN_45nm_BrC FSH74 FSH22 68 FSH FSH FSH ATN (45 nm) ATN (45 nm) Samples IMPROVE X ATN_45nm_BC ATN_45nm_BrC S3673 S49943 S55676 S748 S77493 S75947 S8874 T79 S39744 S9377 S94566 S67593 S9423 S35785 S3964 S43329 S89996 S4654 S76562 S53365 S7247 T62 S79977 S5274 S47447 ATN (45 nm) ATN (45 nm) S2649 S29433 S56928 S6455 S6763 S69959 S882 S8588 S947 S72268 S8252 S4926 S69547 S78737 S66528 S62524 S24674 S3396 S5449 S92 S7344 S5986 S3487 S25245 BrC dominated BC dominated Samples BrC dominated BC dominated Smoldering Biomass ATN_45nm_BC ATN_45nm_BrC BrC dominated Samples Samples * Assuming only BC absorbs at 98 nm and an AAE_BC of to extrapolate BC absorption to 45 nm. * Samples sorted by BrC fraction ( to %) in ATN_45 nm.

17 IMPROVE_A EC PREDICTS ATN_BC BUT OC CORRELATES WITH ATN_BRC r ATN_BC + BrC ATN_BC + BrC ATN (45 nm) ATN_BC y =.4x +.26 R² =.9 y =.37x +. R² =.94 ATN (45 nm) ATN_BC y =.69x +.26 R² =.87 y =.64x.2 R² = ECR (µg/m 3 ) ECR OCR 5 5 ECT (µg/m 3 ) 8 ATN_BrC ECT OCT 8 ATN_BrC ATN (45 nm) Pure BrC y =.2x +.3 R² =.4 ATN (45 nm) y =.2x +.3 R² = OCR (µg/m 3 ) 5 5 OCT (µg/m 3 )

18 POTENTIAL 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

19 CONCLUSIONS 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