Refining temperature measures in thermal/optical carbon analysis

Abstract

Abstract. Thermal/optical methods have been widely used for quantifying total carbon (TC), organic carbon (OC), and elemental carbon (EC) in ambient and source particulate samples. Thermally defined carbon fractions have been used for source identification. Temperature precision in thermal carbon analysis is critical to the allocation of carbon fractions. The sample temperature is determined by a thermocouple, which is usually located in the oven near the sample. Sample and thermocouple temperature may differ owing to different thermal properties between the sample filter punch and the thermocouple, or inhomogeneities in the heating zone. Quick-drying temperature-indicating liquids (Tempil Inc., South Plainfield, NJ) of different liquefying points are used as temperature calibration standards. These consist of chemicals that change their appearance at specific temperatures and can be optically monitored to determine the sample temperature. Temperature measures were evaluated for three different models of carbon analyzers. Sample temperatures were found to differ from sensor temperatures by 10 to 50 • C. Temperature biases of 14 to 22 • C during thermal analysis were found to change carbon fraction measurements. The temperature indicators allow calibration curves to be constructed that relate the sample temperature to the temperature measured by a thermocouple.

U.S. National PM2.5Chemical Speciation Monitoring Networks—CSN and IMPROVE: Description of networks

“…When sampling atmospheric particles, artifacts are typically due to collection of gases on a sampling substrate or volatilization of sample already collected. Determining the impact of an artifact on the measurement may be complicated (e.g., Chow, 1995;Hering and Cass, 1999;Solomon et al, 2000;Turpin et al, 2000;Kim et al, 2001;Pang et al, 2002;Ashbaugh et al, 2004aAshbaugh et al, , 2004bSubramanian et al, 2004;Chow et al, 2005aChow et al, , 2005bKim et al, 2005;White et al, 2005;Yu et al, 2006;Watson et al, 2009;Chow et al, 2010;Maimone et al, 2011). Sampling artifacts are primarily associated with semivolatile components in organic carbon and ammonium nitrate.…”

“…The different temperature protocols are shown in Table 4. The different optical approaches occur during the He temperature steps (Chow et al, 1993;Chow et al, 2001;Chow et al, 2004;Chow et al, 2005a;Chow et al, 2007;Peterson and Richards, 2002;Watson et al, 2005;RTI, 2009e). Beginning in 2008 and finishing in 2009, CSN transitioned to the IMPROVE_A analysis protocol to obtain consistency between the networks.…”

Source Apportionment: Findings from the U.S. Supersites Program

“…10 More specific source markers need to be accurately and efficiently measured at source and receptor to improve SCEs for all of the models. Thermally derived C fractions, [53][54][55][56] which are a free byproduct of thermal/optical C analyses, have been found useful for distinguishing between diesel exhaust and other C source types. [57][58][59][60][61] For example, high-temperature EC (e.g., EC2, EC evolved at 740°C in a 98% helium [He]/2% oxygen [O 2 ] atmosphere) dominates particulate emissions from diesel engines.…”

A Temperature Calibration Procedure for the Sunset Laboratory Carbon Aerosol Analysis Lab Instrument

“…However, temperature variability within the oven may produce a different temperature at the filter than at the temperature sensor. Chow et al (2005) investigated relationships between sample oven temperature sensor measurements and filter temperatures in three thermal-optical instruments-the OGC/DRI Thermal/Optical Carbon Analyzer, the DRI Model 2001 Thermal/Optical Carbon Analyzer, and the Sunset Laboratory Carbon Aerosol Analysis Lab Instrument (called Sunset Instrument herein). These instruments have different hardware configurations (Table 1 in Chow et al 2005) including the placement of the temperature sensor relative to the filter.…”

“…Chow et al (2005) investigated relationships between sample oven temperature sensor measurements and filter temperatures in three thermal-optical instruments-the OGC/DRI Thermal/Optical Carbon Analyzer, the DRI Model 2001 Thermal/Optical Carbon Analyzer, and the Sunset Laboratory Carbon Aerosol Analysis Lab Instrument (called Sunset Instrument herein). These instruments have different hardware configurations (Table 1 in Chow et al 2005) including the placement of the temperature sensor relative to the filter. Sample temperatures were characterized using temperature-indicating materials (Tempilaq • G) that melt and change optical properties at specified temperatures which can be detected by the instrument's optical measurement system.…”