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The influence of temperature calibration on the OC–EC results from a dual-optics thermal carbon analyzer
Citation:
Pavlovic, J., J. S. Kinsey, AND M. D. Hays. The influence of temperature calibration on the OC–EC results from a dual-optics thermal carbon analyzer . Atmospheric Measurement Techniques. Copernicus Publications, Katlenburg-Lindau, Germany, 7:2829-2838, (2014).
Impact/Purpose:
Purpose of this research was to measure the temperature offsets that exist on the Sunset Laboratory Carbon Analyzer and to investigate the influence of temperature calibration on the concentration of each carbon fraction and sub-fraction measured by the NIOSH 5040 and IMPROVE protocols.
Description:
The Sunset Laboratory Dual-Optical Carbonaceous Analyzer that simultaneously measures transmission and reflectance signals is widely used in thermal-optical analysis of particulate matter samples. Most often this instrument is used to measure total carbon (TC), organic carbon (OC), and elemental carbon (EC) fractions, but the analyzer can also measure the thermal sub-fractions of OC and EC for source identification purposes. Although temperature precision in that analysis is highly desirable, a limited number of studies showed that the “real” sample (filter) temperature and the temperature measured by the built-in oven thermocouple (or setpoint temperature) can differ by 10 to 50 ˚C. That temperature disagreement might substantially affect the OC/EC split as well as the OC and EC concentrations. This study systematically examined the new temperature calibration procedure developed by the Sunset Laboratory under NIOSH 5040 and IMPROVE temperature operating conditions. This simple new temperature calibration procedure significantly reduced the temperature differences between the setpoint temperatures and the sample (filter) temperatures, thus providing more confidence in the results. The new temperature calibration procedure significantly changed all NIOSH 5040 carbon fractions (TC, OC, and EC) but did not have a significant influence on the IMPROVE carbon fractions. Almost all NIOSH 5040 and IMPROVE carbon sub-fractions were statistically different after the application of the new temperature calibration procedure. The new calibration procedure increased the already existing disagreement between two the two most widely used thermal-optical protocols.
