Optical Calibration and Equivalence of a Multiwavelength Thermal/Optical Carbon Analyzer

10.4209/aaqr.2015.02.0106

Judith C. Chow；Xiaoliang Wang；Benjamin J. Sumlin；Steven B. Gronstal；L.-W. Antony Chen；Dana L. Trimble；Steven D. Kohl；Sierra R. Mayorga；Gustavo Riggio；Patrick R. Hurbain；Megan Johnson；Ralf Zimmermann；John G. Watson

Brown carbon ； Multiwavelength ； Aerosol light absorption ； Angstrom Absorption Exponent

Aerosol and Air Quality Research

15卷4期（2015 / 08 / 01）

1145 - 1159+i-xxi

英文

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 633nm laser light used for OC charring adjustments with seven wavelengths ranging from 405 to 980nm, including one at 635nm. 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 633nm and 635nm 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.