Refining temperature measures in thermal/optical carbon analysis

[摘要] Thermal/optical methods have been widely used for quantifying total carbon(TC), organic carbon (OC), and elemental carbon (EC) in ambient and sourceparticulate samples. Thermally defined carbon fractions have been used forsource identification. Temperature precision in thermal carbon analysis iscritical to the allocation of carbon fractions. The sample temperature isdetermined by a thermocouple, which is usually located in the oven near thesample. Sample and thermocouple temperature may differ owing to differentthermal properties between the sample filter punch and the thermocouple, orinhomogeneities in the heating zone. Quick-drying temperature-indicatingliquids (Tempil Inc., South Plainfield, NJ) of different liquefying pointsare used as temperature calibration standards. These consist of chemicalsthat change their appearance at specific temperatures and can be opticallymonitored to determine the sample temperature. Temperature measures wereevaluated for three different models of carbon analyzers. Sampletemperatures were found to differ from sensor temperatures by 10 to 50°C.Temperature biases of 14 to 22°C during thermal analysis were foundto change carbon fraction measurements. The temperature indicators allowcalibration curves to be constructed that relate the sample temperature tothe temperature measured by a thermocouple.

[学科分类] 大气科学