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Volume 16, No. 6, June 2016, Pages 1345-1355 PDF(1023 KB)  Supplementary MaterialPDFPDF (581 KB)
doi: 10.4209/aaqr.2015.05.0288   

A Novel Tandem of Thermal Desorption Carbon Analyzer and Off-Axis Integrated Cavity Output Spectroscopy for Aerosol Stable Carbon Isotope Ratio Measurement

Daya S. Kaul1, Zhi Ning1,2, Dane Westerdahl2, Xijie Yin3, Robert A. Cary4

1 School of Energy and Environment, City University of Hong Kong, Hong Kong
2 Guy Carpenter Asia-Pacific Climate Impact Centre, City University of Hong Kong, Hong Kong
3 Laboratory of Ocean and Coast Geology, Third Institute of Oceanography, State Oceanic Administration, Xiamen, China
4 Sunset Laboratory Inc., Tigard, OR, USA

 

Highlights
  • A novel approach for measurement of carbon isotopic ratio of atmospheric aerosols was developed.
  • Organic Carbon-Elemental Carbon and Carbon Dioxide Stable Isotope Analyzers were hyphenated.
  • The approach was validated with National Institute of Standards and Technology standards.
  • The approach produced accurate values of isotopic ratios for different types of aerosols.
  • The approach can produce better than 1‰ precision in stable isotope ratio estimation.

Abstract

 

A novel approach for measurement of stable carbon isotopic ratio of atmospheric aerosols was developed by tandem operation of two instruments: a Sunset Organic Carbon-Elemental Carbon (OC-EC) analyzer and an online Carbon Dioxide Stable Isotope Analyzer (LGR, CCIA-36d). Sensitivity, accuracy and measurement uncertainty of the CCIA was comprehensively investigated using the standard reference CO2 gas with known concentration and isotopic ratio. Drift in CCIA measurement due to varying CO2 and water vapor concentration was evaluated and a humidity stabilizer was designed and developed to control the water vapor concentration of exhaust gas flow from OC-EC prior to entering the CCIA. A Keeling approach was applied to separate the ratio in the samples from the mixture of PM sample-produced CO2 and reference gas and we developed a protocol to derive the isotopic composition of the particle samples. A lithium carbonate standard (in powder form) from National Institute of Standards and Technology (NIST) was used to validate measurement of δ13C ratios by CCIA. Offline measurement on ambient aerosol and diesel exhaust aerosols produced comparable results of isotopic ratio with literature values. This study demonstrates the utility of this tandem operation for carbon isotopic measurement of atmospheric particles with better than 1.0‰ precision as a cost-effective alternative of conventional Isotopic Ratio Mass Spectrometer (IR-MS).

 

 

Keywords: OC-EC; OA-ICOS; Keeling curve; Stable isotopic ratio; Organic aerosol.

 

 

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