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
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.Determination of the temperature upper-limit for low-temperature oxidation
Criterion: EC remains intact.
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
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.
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
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