Response of Two Total Carbon Analyzers to Various Aerosols

JOEL CORBIN, Daniel Clavel, Timothy Sipkens, Gregory Smallwood, National Research Council Canada

     Abstract Number: 363
     Working Group: Instrumentation and Methods

Abstract
Particulate matter (PM) in the atmosphere and in combustion emissions is often dominated in mass by carbon. The total carbon mass (TC) can be converted to total PM mass if the mass fraction of heteroatoms such as O and H is known. TC can be viewed as the sum of organic carbon (OC, a proxy for volatile organic compounds) and elemental carbon (EC, a proxy for black carbon) as defined by thermal-optical analysis (TOA) or similar techniques. No matter what technique is used, the division of TC into specific species tends to result in operationally defined categories, since carbonaceous materials often have a continuum of properties. The overlap between properties can be severe (such as for heavy fuel oil and biomass burning) or negligible (such as for mixtures of lubrication oil or secondary organic aerosols with soot). Additionally, categorization tends to come at the sacrifice of sensitivity in TOA and other techniques.

To address some of the above concerns and the need for simpler TC measurements, two instruments have recently been introduced: the Magee TCA08 (Aerosol doo, Slovenia) and the fast thermal carbon totalizer (FATCAT; University of Northwestern Switzerland FHNW, Switzerland). Both of these instruments collect PM on internal filters; heat the samples to ~1000 K over ~1 minute in air; and measure any evolved CO2 using NDIR detectors. However, there are some significant differences. The TCA08 uniquely uses quartz fibre filters similar to those used in TOA; heats samples in an oven containing metal coils; and is already in commercial production. The FATCAT uniquely uses a metal filter which is heated directly by induction; and includes a catalyst to convert all hydrocarbon evolved gases to CO2.

In this work, we systematically explored the ability of the TCA08 and FATCAT to serve as a TC measurement devices for potential regulatory applications. Due to the lack of a CO2 conversion catalyst, the TCA08 response factor to organics (“OC”: sucrose, dioctyl sebacate, and hexadecane) was an order of magnitude different to that for soot (“EC”). Consequently, the calibration factor is also a function of the EC/TC ratio. The corresponding FATCAT response factor showed a negligible dependence on the composition of the PM. Repeatability for samples of similar composition was excellent for both instruments. We have also explored the potential use of the carbon analyzers’ thermograms for distinguishing various carbons and will discuss the results.