Technical note: Common glitch affecting the EC/OC split point determination in the Sunset Thermal-Optical Analyzerand recommendations to reduce its occurrence

Abstract. We identified a common and relatively frequent glitch in the light transmittance/reflectance measurement during thermal-optical analysis in the Sunset Laboratory bench top thermal-optical analyzer models. In the instrument studied, the glitch is observed for one in three punch analyses when using the default analysis parameters. The occurrence of this glitch can invalidate the split point and thus the OC and EC fractions and absolute quantities reported. The glitch was observed in data from at least three independent laboratories using different thermal protocols. We describe this glitch as a “discontinuity” (rapid increase or decrease occurring over a few seconds) in the laser transmittance or reflectance which happens relatively frequently and whose behaviour varies in amplitude, timing and direction. We use over 2,200 filter-punch analyses to expose the factors that contribute to the risk of such a discontinuity occurring. We demonstrate that these discontinuities are due to the movement of filter punches within the instrument, and can therefore be minimized by decreasing the blower speed of the instrument and, if possible, by ensuring a tighter fit of the filter punch in its holder (by testing different spoons). The decrease in blower speed has a negligible effect on the measured temperature program during analysis and is the single most effective way to reduce the risk of discontinuity occurrence. We recommend these modifications for all Sunset instruments.

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Toward a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol

Atmospheric Measurement Techniques ◽

10.5194/amt-3-79-2010 ◽

2010 ◽

Vol 3 (1) ◽

pp. 79-89 ◽

Cited By ~ 509

Author(s):

F. Cavalli ◽

M. Viana ◽

K. E. Yttri ◽

J. Genberg ◽

J.-P. Putaud

Keyword(s):

Elemental Carbon ◽

Thermal Evolution ◽

Standard Procedure ◽

Pyrolytic Carbon ◽

Total Carbon ◽

Carbonaceous Aerosol ◽

Optical Analysis ◽

Split Point ◽

Aerosol Fraction ◽

Eu Project

Abstract. Thermal-optical analysis is a conventional method for determining the carbonaceous aerosol fraction and for classifying it into organic carbon, OC, and elemental carbon, EC. Unfortunately, the different thermal evolution protocols in use can result in a wide elemental carbon-to-total carbon variation by up to a factor of five. In Europe, there is currently no standard procedure for determining the carbonaceous aerosol fraction which implies that data from different laboratories at various sites are of unknown accuracy and cannot be considered comparable. In the framework of the EU-project EUSAAR (European Supersites for Atmospheric Aerosol Research), a comprehensive study has been carried out to identify the causes of differences in the EC measured using different thermal evolution protocols; thereby the major positive and negative biases affecting thermal-optical analysis have been isolated and minimised to define an optimised protocol suitable for European aerosols. Our approach to improve the accuracy of the discrimination between OC and EC was essentially based on four goals. Firstly, charring corrections rely on faulty assumptions – e.g. pyrolytic carbon is considered to evolve completely before native EC throughout the analysis –, thus we have reduced pyrolysis to a minimum by favoring volatilisation of OC. Secondly, we have minimised the potential negative bias in EC determination due to early evolution of light absorbing carbon species at higher temperatures in the He-mode, including both native EC and combinations of native EC and pyrolytic carbon potentially with different specific attenuation cross section values. Thirdly, we have minimised the potential positive bias in EC determination resulting from the incomplete evolution of OC during the He-mode which then evolves during the He/O2-mode, potentially after the split point. Finally, we have minimised the uncertainty due to the position of the OC/EC split point on the FID response profile by introducing multiple desorption steps in the He/O2-mode. Based on different types of carbonaceous PM encountered across Europe, we have defined an optimised thermal evolution protocol, the EUSAAR_2 protocol, as follows: step 1 in He, 200 °C for 120 s; step 2 in He 300 °C for 150 s; step 3 in He 450 °C for 180 s; step 4 in He 650 °C for 180 s. For steps 1–4 in He/O2, the conditions are 500 °C for 120 s, 550 °C for 120 s, 700 ° C for 70 s, and 850 °C for 80 s, respectively.

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Thermal-optical analysis for the measurement of elemental carbon (EC) and organic carbon (OC) in ambient air a literature review

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-9649-2015 ◽

2015 ◽

Vol 8 (9) ◽

pp. 9649-9712 ◽

Cited By ~ 42

Author(s):

A. Karanasiou ◽

M. C. Minguillón ◽

M. Viana ◽

A. Alastuey ◽

J.-P. Putaud ◽

...

Keyword(s):

Organic Carbon ◽

Literature Review ◽

Elemental Carbon ◽

Ambient Air ◽

Correction Method ◽

Total Carbon ◽

Light Transmittance ◽

Critical Parameters ◽

Optical Analysis ◽

The Difference

Abstract. Thermal-optical analysis is currently under consideration by the European standardization body (CEN) as the reference method to quantitatively determine organic carbon (OC) and elemental carbon (EC) in ambient air. This paper presents an overview of the critical parameters related to the thermal-optical analysis including thermal protocols, critical factors and interferences of the methods examined, method inter-comparisons, inter-laboratory exercises, biases and artifacts, and reference materials. The most commonly used thermal protocols include NIOSH-like, IMPROVE_A and EUSAAR_2 protocols either with light transmittance or reflectance correction for charring. All thermal evolution protocols are comparable for total carbon (TC) concentrations but the results vary significantly concerning OC and especially EC concentrations. Thermal protocols with a rather low peak temperature in the inert mode like IMPROVE_A and EUSAAR_2 tend to classify more carbon as EC compared to NIOSH-like protocols, while charring correction based on transmittance usually leads to smaller EC values compared to reflectance. The difference between reflectance and transmittance correction tends to be larger than the difference between different thermal protocols. Nevertheless, thermal protocols seem to correlate better when reflectance is used as charring correction method. The difference between EC values as determined by the different protocols is not only dependent on the optical pyrolysis correction method, but also on the chemical properties of the samples due to different contributions from various sources. The overall conclusion from this literature review is that it is not possible to identify the "best" thermal-optical protocol based on literature data only, although differences attributed to the methods have been quantified when possible.

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Common glitch affecting the EC/OC split point determination

10.5194/amt-2019-298-rc2 ◽

2019 ◽

Author(s):

Anonymous

Keyword(s):

Split Point ◽

Point Determination

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

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-7-3321-2014 ◽

2014 ◽

Vol 7 (4) ◽

pp. 3321-3348 ◽

Cited By ~ 2

Author(s):

J. Pavlovic ◽

J. S. Kinsey ◽

M. D. Hays

Keyword(s):

Elemental Carbon ◽

Calibration Procedure ◽

Carbonaceous Aerosol ◽

Temperature Calibration ◽

Wide Spread ◽

Optical Analysis ◽

Point Selection ◽

Sample Composition ◽

Improve Accuracy ◽

Split Point

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 NIOSH 5040 and IMPROVE protocols. 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 wide-spread 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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Toward a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-2-2321-2009 ◽

2009 ◽

Vol 2 (5) ◽

pp. 2321-2345 ◽

Cited By ~ 8

Author(s):

F. Cavalli ◽

M. Viana ◽

K. E. Yttri ◽

J. Genberg ◽

J.-P. Putaud

Keyword(s):

Elemental Carbon ◽

Thermal Evolution ◽

Standard Procedure ◽

Pyrolytic Carbon ◽

Total Carbon ◽

Carbonaceous Aerosol ◽

Optical Analysis ◽

Split Point ◽

Aerosol Fraction ◽

Eu Project

Abstract. Thermal-optical analysis is a conventional method for determining the carbonaceous aerosol fraction and for classifying it into organic carbon, OC, and elemental carbon, EC. Unfortunately, the different thermal evolution protocols in use can result in a wide elemental carbon-to-total carbon variation by up to a factor of five. In Europe, there is currently no standard procedure for determining the carbonaceous aerosol fraction which implies that data from different laboratories at various sites are of unknown accuracy and cannot be considered comparable. In the framework of the EU-project EUSAAR (European Supersites for Atmospheric Aerosol Research), a comprehensive study has been carried out to identify the causes of differences in the EC measured using different thermal evolution protocols; thereby the major positive and negative biases affecting thermal-optical analysis have been isolated and minimised to define an optimised protocol suitable for European aerosols. Our approach to improve the accuracy of the discrimination between OC and EC was essentially based on four goals. Firstly, charring corrections rely on faulty assumptions – e.g. pyrolytic carbon is considered to evolve completely before native EC throughout the analysis –, thus we have reduced pyrolysis to a minimum by favoring volatilisation of OC. Secondly, we have minimised the potential negative bias in EC determination due to early evolution of light absorbing carbon species at higher temperatures in the He-mode, including both native EC and combinations of native EC and pyrolytic carbon potentially with different specific cross section values. Thirdly, we have minimised the potential positive bias in EC determination resulting from the incomplete evolution of OC during the He-mode which then evolves during the He/O2-mode, potentially after the split point. Finally, we have minimised the uncertainty due to the position of the OC/EC split point on the FID response profile by introducing multiple desorption steps in the He/O2-mode. Based on different types of carbonaceous PM encountered across Europe, we have defined an optimised thermal evolution protocol, the EUSAAR_2 protocol, as follows: step 1 in He, 200°C for 120 s; step 2 in He 300°C for 150 s; step 3 in He 450°C for 180 s; step 4 in He 650°C for 180 s. For steps 1–4 in He/O2, the conditions are 500°C for 120 s, 550°C for 120 s, 700°C for 70 s, and 850°C for 80 s, respectively.

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New AAC Access Strategy for Gesture Tracking: A Technical Note

Perspectives on Augmentative and Alternative Communication ◽

10.1044/aac21.1.11 ◽

2012 ◽

Vol 21 (1) ◽

pp. 11-16 ◽

Cited By ~ 1

Author(s):

Susan Fager ◽

Tom Jakobs ◽

David Beukelman ◽

Tricia Ternus ◽

Haylee Schley

Keyword(s):

Augmentative And Alternative Communication ◽

Technical Note ◽

Head Tracking ◽

Alternative Communication ◽

Access Methods ◽

Cord Injury ◽

Physical Limitations ◽

Gesture Tracking ◽

Communication Needs ◽

Tracking Device

Abstract This article summarizes the design and evaluation of a new augmentative and alternative communication (AAC) interface strategy for people with complex communication needs and severe physical limitations. This strategy combines typing, gesture recognition, and word prediction to input text into AAC software using touchscreen or head movement tracking access methods. Eight individuals with movement limitations due to spinal cord injury, amyotrophic lateral sclerosis, polio, and Guillain Barre syndrome participated in the evaluation of the prototype technology using a head-tracking device. Fourteen typical individuals participated in the evaluation of the prototype using a touchscreen.

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