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

Abstract

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.

Changes in PM<sub>2.5</sub> peat combustion source profiles with atmospheric aging in an oxidation flow reactor

“…Half of the quartz-fiber filter (i.e., channels two and six) was analyzed for (1) four anions (i.e., chloride, Cl − ; nitrite, NO − 2 ; nitrate, NO − 3 ; and sulfate, SO = 4 ), three cations (i.e., water-soluble sodium, Na + ; potassium, K + ; and ammonium, NH + 4 ), and nine organic acids (including four mono-and five dicarboxylic acids) by ion chromatography (IC) with a conductivity detector (CD) ; (2) 17 carbohydrates including levoglucosan and its isomers by IC with a pulsed amperometric detector (PAD); and (3) WSOC by combustion and nondispersive infrared (NDIR) detection. A portion (0.5 cm 2 ) of the other half quartz-fiber filter was analyzed for OC, EC, and brown carbon (BrC) by the IMPROVE_A multiwavelength thermal-optical reflectancetransmittance method Chow et al, 2007Chow et al, , 2015b; the IMPROVE_A protocol reports eight operationally defined thermal fractions (i.e., OC1 to OC4 evolved at 140, 280, 480, and 580 • C in helium atmosphere; EC1 to EC3 evolved at 580, 740, and 840 • C in helium-oxygen atmosphere; and pyrolyzed carbon, OP) that further characterize carbon properties under different combustion and aging conditions. Citric acid-and sodium chloride-impregnated cellulose-fiber filters placed behind the Teflon-membrane and quartz-fiber filters, respectively, ac-Figure 1.…”

Feasibility of coupling a thermal/optical carbon analyzer to a quadrupole mass spectrometer for enhanced PM2.5 speciation

“…The soil is calculated using the following formula: Soil = 2.2Al + 2.49Si + 1.63Ca +1.94Ti + 2.42Fe (Malm et al 1994 This setup is a practical possibility for the newly designed DRI model 2015 TOA (McGee Scientific, Berkeley, CA). This instrument also allows for simultaneous determination of multiwavelength light absorption and separation of brown carbon from black carbon Chow et al, 2015b), as well as providing more precise sample heating that can better bracket the decomposition temperatures of different compounds found in suspended particles (MacKenzie 1970).…”

“…(2) water-soluble ammonium (NH 4 + ), nitrate (NO 3 − ), sulfate (SO 4 2-), chloride (Cl − ), sodium (Na + ), and potassium (K + ) by ion chromatography (IC) (Chow andWatson 1999, 2017); and (3) organic carbon (OC) and elemental carbon (EC) with a thermal/optical analyzer (TOA) (Chow et al 2007(Chow et al , 1993b. With appropriate weighting for unmeasured hydrogen (H) and oxygen (O) components in geological material and organic matter (OM), the PM 2.5 gravimetric mass can be reproduced with reasonable accuracy (Chow et al 2015a).…”

Filter Processing and Gravimetric Analysis for Suspended Particulate Matter Samples

“…Quartz-fiber filters are commonly used for carbon (Chow et al 1993(Chow et al , 2007(Chow et al , 2015b and ion analyses (Chow andWatson 1999, 2017), with a parallel Teflon sample used for gravimetric analysis. Quartz filters adsorb organic vapors (Chow et al 2010;Watson et al 2009), which yields a positive bias to gravimetric measurements.…”