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

Phuah, Chin H.; Peterson, Max R.; Richards, Melville; Turner, Jay; Dillner, Ann M.

doi:10.1080/02786820903124698

Cited by 24 publications

(27 citation statements)

References 11 publications

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“…The classification of OC and EC is widely acknowledged, but their boundary is still not clear and highly operationaldependent (Schmid et al, 2001;Pöschl, 2005). Among the commonly accepted OC/EC determination methods, the thermal-optical analysis (TOA) method is one of the most well-known techniques (Schmid et al, 2001;Chow et al, 2004;Phuah et al, 2009;Cavalli et al, 2010). It typically begins with a heating step in an inert (i.e.…”

Section: Introductionmentioning

confidence: 99%

On the isolation of OC and EC and the optimal strategy of radiocarbon-based source apportionment of carbonaceous aerosols

Zhang¹,

Perron²,

Ciobanu³

et al. 2012

Preprint

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Radiocarbon (14C) measurements of elemental carbon (EC) and organic carbon (OC) separately (as opposed to only total carbon, TC) allow an unambiguous quantification of their non-fossil and fossil sources and represent an improvement in carbonaceous aerosol source apportionment. Isolation of OC and EC for accurate 14C determination requires complete removal of interfering fractions with maximum recovery. To evaluate the extent of positive and negative artefacts during OC and EC separation, we performed sample preparation with a commercial Thermo-Optical OC/EC Analyser (TOA) by monitoring the optical properties of the sample during the thermal treatments. Extensive attention has been devoted to the set-up of TOA conditions, in particular, heating program and choice of carrier gas. Based on different types of carbonaceous aerosols samples, an optimised TOA protocol (Swiss_4S) with four steps is developed to minimise the charring of OC, the premature combustion of EC and thus artefacts of 14C-based source apportionment of EC. For the isolation of EC for 14C analysis, the water-extraction treatment on the filter prior to any thermal treatment is an essential prerequisite for subsequent radiocarbon; otherwise the non-fossil contribution may be overestimated due to the positive bias from charring. The Swiss_4S protocol involves the following consecutive four steps (S1, S2, S3 and S4): (1) S1 in pure oxygen (O2) at 375 °C for separation of OC for untreated filters, and water-insoluble organic carbon (WINSOC) for water-extracted filters; (2) S2 in O2 at 475 °C, followed by (3) S3 in helium (He) at 650 °C, aiming at complete OC removal before EC isolation and leading to better consistency with thermal-optical protocols like EUSAAR_2, compared to pure oxygen methods; and (4) S4 in O2 at 760 °C for recovery of the remaining EC. WINSOC was found to have a significantly higher fossil contribution than the water-soluble OC (WSOC). Moreover, the experimental results demonstrate the lower refractivity of wood-burning EC compared to fossil EC and the difficulty of clearly isolating EC without premature evolution. Hence, simplified techniques of EC isolation for 14C analysis are prone to a substantial bias and generally tend towards an underestimation of the non-fossil sources. Consequently, the optimal strategy for 14C-based source apportionment of carbonaceous aerosols should follow an approach to subdivide TC into different carbonaceous aerosol fractions for individual 14C analyses, as these fractions differ in their origins. To obtain the comprehensive picture of the sources of carbonaceous aerosols, the Swiss_4S protocol is not only implemented to measure OC and EC fractions, but also WINSOC as wel...

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Section: Introductionmentioning

confidence: 99%

On the isolation of OC and EC and the optimal strategy of radiocarbon-based source apportionment of carbonaceous aerosols

Zhang¹,

Perron²,

Ciobanu³

et al. 2012

Preprint

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“…Seventeen different laboratories equipped with similar instrumentation followed similar calibration procedures, including those for temperature (Phuah et al, 2009). For EC, the standard deviation among laboratories was 25.5% for the NIOSH870 and 19.5% for the EUSSAR2 protocols.…”

Section: Panteliadis Et Al's (2014) Recent Interlaboratory Comparisomentioning

confidence: 99%

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

Chow

Wang

Sumlin

et al. 2015

Aerosol Air Qual. Res.

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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.

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“…In addition, Tempilaq • G can only be tested at temperatures for which the calibration liquids are available, not at real operating filter temperatures. More recently, Phuah et al (2009) confirmed the oven-filter temperature discrepancy on four different Sunset Laboratory instruments and reported statistically insignificant differences for the IMPROVE total carbon (TC), OC, and EC concentrations after temperature calibration. The calibration method developed in that study involved a simple hardware change by way of a temperature probe introduction that did not harm the instrument.…”

Section: Introductionmentioning

confidence: 83%

“…A temperature bias of up to 50 • C was observed, but did not influence the OC and EC concentrations measured with the IMPROVE protocol. Limitations of the temperature calibration method for the DRI analyzer include use of temperature-indicating (Tempilaq • G, Tempil Inc., South Plainfield, NJ, USA) liquids that damage the quartz surfaces of the sample holder and oven, poison the oxidation catalyst, and contaminate downstream components, as noted in Phuah et al (2009). In addition, Tempilaq • G can only be tested at temperatures for which the calibration liquids are available, not at real operating filter temperatures.…”

Section: Introductionmentioning

confidence: 99%

The influence of temperature calibration on the OC–EC results from a dual-optics thermal carbon analyzer

2014

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Abstract. Thermal–optical analysis (TOA) is a widely used technique that fractionates carbonaceous aerosol particles into organic and elemental carbon (OC and EC), or carbonate. Thermal sub-fractions of evolved OC and EC are also used for source identification and apportionment; thus, oven temperature accuracy during TOA analysis is essential. Evidence now indicates that the "actual" sample (filter) temperature and the temperature measured by the built-in oven thermocouple (or set-point temperature) can differ by as much as 50 °C. This difference can affect the OC–EC split point selection and consequently the OC and EC fraction and sub-fraction concentrations being reported, depending on the sample composition and in-use TOA method and instrument. The present study systematically investigates the influence of an oven temperature calibration procedure for TOA. A dual-optical carbon analyzer that simultaneously measures transmission and reflectance (TOT and TOR) is used, functioning under the conditions of both the National Institute of Occupational Safety and Health Method 5040 (NIOSH) and Interagency Monitoring of Protected Visual Environment (IMPROVE) protocols. The application of the oven calibration procedure to our dual-optics instrument significantly changed NIOSH 5040 carbon fractions (OC and EC) and the IMPROVE OC fraction. In addition, the well-known OC–EC split difference between NIOSH and IMPROVE methods is even further perturbed following the instrument calibration. Further study is needed to determine if the widespread application of this oven temperature calibration procedure will indeed improve accuracy and our ability to compare among carbonaceous aerosol studies that use TOA.

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

Cited by 24 publications

References 11 publications

On the isolation of OC and EC and the optimal strategy of radiocarbon-based source apportionment of carbonaceous aerosols

On the isolation of OC and EC and the optimal strategy of radiocarbon-based source apportionment of carbonaceous aerosols

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

The influence of temperature calibration on the OC–EC results from a dual-optics thermal carbon analyzer

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