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. 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 Carrier gasTemperature ( o C)Time (sec) He He-1 He-2 50 600 800 Purging online 60 300 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 800 o C  FID signal remains at baseline.  No discernable increase in filter laser transmittance is observed.

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

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

7. Earlier Work Using a Low-temperature Oxidation Step in thermal analysis:  Optimal temperature for OC/EC: 300-350 o C, (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 o C, pure O 2, 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 IMPROVENIOSHOptimized-1Optimized-2 HePurging online (10s) O 2 /He200s, 350 o C He-1180 s, 120 o C60 s, 250 o C10s, purging He-2180 s, 250 o C60 s, 500 o C He-3180 s, 450 o C60 s, 650 o C He-4180 s, 550 o C90 s, 850 o C 200 s, 850 o C He-5Purging, 60 s O 2 /He-1240 s, 550 o C30 s, 650 o C O 2 /He-2210 s, 700 o C30 s, 750 o C O 2 /He-3210 s, 800 o C60 s, 850 o C O 2 /He-4120 s, 940 o C

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

11. low high C loading

12. low high C loading

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