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Charring Minimization in Thermal Analysis of Aerosol Carbon

Charring Minimization in Thermal Analysis of Aerosol Carbon. Jian Zhen Yu and Qianfeng Li Department of Chemistry Hong Kong University of Science & Technology. EC/OC workshop, Durango, CO March 2003. Thermal conditions that maximize OC removal / minimize charring of OC.

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Charring Minimization in Thermal Analysis of Aerosol Carbon

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  1. Charring Minimization in Thermal Analysis of Aerosol Carbon Jian Zhen Yu and Qianfeng Li Department of Chemistry Hong Kong University of Science & Technology EC/OC workshop, Durango, CO March 2003

  2. Thermal conditions that maximize OC removal / minimize charring of OC • Low-temperature oxidation (Cadle et al., 1983; Cachier et al., 1989) • Flash heating (Tanner et al., 1982)

  3. Criterion: EC remains intact. Determination of the temperature upper-limit for low-temperature oxidation We need EC materials that are free of OC and representative of aerosol EC .

  4. Thermal Creation of EC-Only Test Samples from Atmospheric Aerosols Thermal conditions for creation of EC-only (mixture of PEC and native aerosol EC) samples • Successful creation of EC-only samples is evidenced by: • In He atmosphere at temperatures as high as 800oC • FID signal remains at baseline. • No discernable increase in filter laser transmittance is observed.

  5. Thermal evolution of an EC-only sample in 2% O2/He

  6. Percentage of EC Evolved as a Function of Oxidation Temperature 350 oC

  7. Earlier Work Using a Low-temperature Oxidation Step in thermal analysis: • Optimal temperature for OC/EC: 300-350 oC, (Dod et al., 1978; Ellis et al., 1984; Ohta and Okita, 1984). • 2-step method for OC/EC (Cachier et. al., Tellus, 1989, 41B, 379). 340 oC, pure O2 , precombustion 2 hours. Pure graphite was intact.

  8. Flash Heating Kinetics Competition: Vaporization versus Decomposition Ref:Buehler R.J., et.al. J.Am. Chem.Soc. “Proton Transfer Mass Spectrometry of Peptides. A Rapid Heating Technique for Underivatized Peptides Containing Arginine”, 1974, 96, 3990

  9. Thermal Methods Used for Comparison

  10. Combination of low-temperature oxidation and flash heating forms least charring from water-soluble aerosol OC

  11. C loading high low

  12. C loading high low

  13. Transmittance Increase before the OCEC split in the He/O2 step Smaller transmittance increase is expected with lower amount of charring.

  14. Deviation of EC measurements by non-optimal methods from the optimized method

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