Volume 15, No. 4, August 2015, Pages 1145-1159 PDF(5.63 MB)
Optical Calibration and Equivalence of a Multiwavelength Thermal/Optical Carbon Analyzer
Judith C. Chow1,2,3, Xiaoliang Wang1,3, Benjamin J. Sumlin1, Steven B. Gronstal1, L.-W. Antony Chen1,4, Dana L. Trimble1, Steven D. Kohl1, Sierra R. Mayorga1, Gustavo Riggio1, Patrick R. Hurbain1, Megan Johnson1, Ralf Zimmermann5, John G. Watson1,2,3
1 Division of Atmospheric Sciences, Desert Research Institute, Reno, Nevada 89512, USA
2 The State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, Shaanxi, 710075, China
3 Graduate Faculty, University of Nevada, Reno, Nevada 89503, USA
4 Department of Environmental and Occupational Health, University of Nevada, Las Vegas, Nevada 89154, USA
5 Joint Mass Spectrometry Centre, Chair of Analytical Chemistry, Institute of Chemistry, University of Rostock, Rostock, Germany
- A multi-wavelength carbon analyzer quantifies brown carbon.
- PM2.5 optical properties by carbon analysis can be traceable to primary standards.
- Trends in OC and EC are not affected by multi-wavelength pyrolysis corrections.
Organic and elemental carbon (OC and EC) are operationally-defined by the measurement process, so long-term trends may be interrupted with instrumentation changes. A modification to the U.S. IMPROVE carbon analysis protocol and hardware is examined that replaces the 633 nm laser light used for OC charring adjustments with seven wavelengths ranging from 405 to 980 nm, including one at 635 nm. Reflectance (R) and Transmittance (T) values for each wavelength are made traceable to primary standards through transfer standards consisting of a range of aerosol deposits on filter media similar to that of the analyzed samples. R and T values are assigned to these filters using a UV/VIS spectrometer calibrated with these standards. Using ambient and source (e.g., diesel exhaust, flaming biomass, and smoldering biomass) samples, it is demonstrated that R and T calibration is independent of the sample type. Total carbon (TC), OC, and EC comparisons with the earlier hardware design for urban- and non-urban samples demonstrate equivalence, within precisions derived from replicate analyses, for the 633 nm and 635 nm wavelengths. Several uses of the additional multiwavelength information are identified, including: 1) ground-truthing of multi-spectral remote sensors; 2) improving estimates of the Earth’s radiation balance; 3) associating specific organic compounds with their light absorption properties; and 4) appropriating sources of black and brown carbon.
Brown carbon; Multiwavelength; Aerosol light absorption; Angstrom Absorption Exponent.