Improved measurement of carbonaceous aerosol in Beijing, China: intercomparison of sampling and thermal-optical analysis methods

Abstract. The sampling artifacts (both positive and negative) and the influence of thermal-optical methods (both charring correction method and the peak inert mode temperature) on the split of organic carbon (OC) and elemental carbon (EC) were evaluated in Beijing. The positive sampling artifact constituted 10% and 23% of OC concentration determined by the bare quartz filter during winter and summer, respectively. For summer samples, the adsorbed gaseous organics were found to continuously evolve off the filter during the whole inert mode when analyzed by the IMPROVE-A temperature protocol. This may be due to the oxidation of the adsorbed organics during sampling (reaction artifact) which would increase their thermal stability. The backup quartz approach was evaluated by a denuder-based method for assessing the positive artifact. The quartz-quartz (QBQ) in series method was demonstrated to be reliable, since all of the OC collected by QBQ was from originally gaseous organics. Negative artifact that could be adsorbed by quartz filter was negligible. When the activated carbon impregnated glass fiber (CIG) filter was used as the denuded backup filter, the denuder efficiency for removing gaseous organics that could be adsorbed by the CIG filter was only about 30%. EC values were found to differ by a factor of about two depending on the charring correction method. Influence of the peak inert mode temperature was evaluated based on the summer samples. The EC value was found to continuously decrease with the peak inert mode temperature. Premature evolution of light absorbing carbon began when the peak inert mode temperature was increased from 580 to 650 °C; when further increased to 800 °C, the OC and EC split frequently occurred in the He mode, and the last OC peak was characterized by the overlapping of two separate peaks. The discrepancy between EC values defined by different temperature protocols was larger for Beijing carbonaceous aerosol compared with North America and Europe, perhaps due to the higher concentration of brown carbon in Beijing aerosol.

Download Full-text

Improved measurement of carbonaceous aerosol: evaluation of the sampling artifacts and inter-comparison of the thermal-optical analysis methods

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-8533-2010 ◽

2010 ◽

Vol 10 (17) ◽

pp. 8533-8548 ◽

Cited By ~ 27

Author(s):

Y. Cheng ◽

K. B. He ◽

F. K. Duan ◽

M. Zheng ◽

Y. L. Ma ◽

...

Keyword(s):

Thermal Stability ◽

Elemental Carbon ◽

Correction Method ◽

Optical Methods ◽

Carbonaceous Aerosol ◽

Series Method ◽

Optical Analysis ◽

Quartz Filter ◽

Sampling Artifacts ◽

In Series

Download Full-text

Measurement of carbonaceous aerosol with different sampling configurations and frequencies

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-3171-2015 ◽

2015 ◽

Vol 8 (3) ◽

pp. 3171-3198

Author(s):

Y. Cheng ◽

K.-B. He

Keyword(s):

Water Vapor ◽

High Frequency ◽

Elemental Carbon ◽

Low Frequency ◽

Correction Method ◽

Carbonaceous Aerosol ◽

High Humidity ◽

Optical Attenuation ◽

Shadowing Effect ◽

Beijing China

Abstract. Carbonaceous aerosol in Beijing, China was measured with different sampling configurations (denuded vs. un-denuded) and frequencies (24 vs. 48 h averaged). Our results suggest that the negative sampling artifact of a bare quartz filter could be remarkably enhanced due to the uptake of water vapor by the filter medium, indicating that the positive sampling artifact tends to be underestimated under high humidity conditions. It was also observed that the analytical artifact (i.e., the underestimation of elemental carbon by the operationally defined value of the thermal-optical method) was more apparent for the low frequency samples such that their elemental carbon (EC) concentrations were about 15% lower than the reference values measured by the high-frequency, denuded filters. Moreover, EC results of the low frequency samples were found to exhibit a stronger dependence on the charring correction method. In addition, optical attenuation (ATN) of EC was retrieved from the carbon analyzer, and the low frequency samples were shown to be more significantly biased by the shadowing effect.

Download Full-text

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

A newly identified calculation discrepancy of the Sunset semi-continuous carbon analyzer

Atmospheric Measurement Techniques ◽

10.5194/amt-7-1969-2014 ◽

2014 ◽

Vol 7 (7) ◽

pp. 1969-1977 ◽

Cited By ~ 8

Author(s):

G. J. Zheng ◽

Y. Cheng ◽

K. B. He ◽

F. K. Duan ◽

Y. L. Ma

Keyword(s):

Occupational Safety ◽

Single Point ◽

Correction Method ◽

Total Carbon ◽

Carbonaceous Aerosol ◽

Optical Data ◽

Baseline Correction ◽

Safety And Health ◽

Corrected Data ◽

Carbon Load

Abstract. The Sunset semi-continuous carbon analyzer (SCCA) is an instrument widely used for carbonaceous aerosol measurement. Despite previous validation work, in this study we identified a new type of SCCA calculation discrepancy caused by the default multipoint baseline correction method. When exceeding a certain threshold carbon load, multipoint correction could cause significant total carbon (TC) underestimation. This calculation discrepancy was characterized for both sucrose and ambient samples, with two protocols based on IMPROVE (Interagency Monitoring of PROtected Visual Environments) (i.e., IMPshort and IMPlong) and one NIOSH (National Institute for Occupational Safety and Health)-like protocol (rtNIOSH). For ambient samples, the IMPshort, IMPlong and rtNIOSH protocol underestimated 22, 36 and 12% of TC, respectively, with the corresponding threshold being ~ 0, 20 and 25 μgC. For sucrose, however, such discrepancy was observed only with the IMPshort protocol, indicating the need of more refractory SCCA calibration substance. Although the calculation discrepancy could be largely reduced by the single-point baseline correction method, the instrumental blanks of single-point method were higher. The correction method proposed was to use multipoint-corrected data when below the determined threshold, and use single-point results when beyond that threshold. The effectiveness of this correction method was supported by correlation with optical data.

Download Full-text