Charring Minimization in Thermal Analysis of Aerosol Carbon

Jian Zhen Yu and Qianfeng LiDepartment 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

Low-temperature oxidation (Cadle et al., 1983; Cachier et al.,

1989)

Flash heating (Tanner et al., 1982)

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 .

Thermal Creation of EC-Only Test Samples from Atmospheric Aerosols

Carrier gas Temperature (oC) Time (sec)

HeHe-1He-2

50600800

Purging online60300

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 800oCFID signal remains at baseline.No discernable increase in filter laser transmittance is observed.

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

0 200 400 600 800 1000 12000

100

200

300

400

500

600

700

800

900

Hong Kong sample

Te

mp

era

ture

(o C

)

Time (sec)

FID response

TransmittanceTemperature

Percentage of EC Evolved as a Function of Oxidation Temperature

0 100 200 300 400 500 600 700 8000

20

40

60

80

100

Pe

rce

nta

ge

EC

Evo

lve

d (

%)

Temperature (oC)

Qingdao-1 (China) Qingdao-2 (China) Nanjing-1 (China) Nanjing-2 (China) Hong Kong-1 Hong Kong-2 Hong Kong-3 Hong Kong-4 Korea-1 Korea-2

350 oC

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.

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

Thermal Methods Used for Comparison IMPROVE NIOSH Optimized-1 Optimized-2

He Purging online (10s)

O2/He 200s, 350 oC 200s, 350 oC

He-1 180 s, 120 oC 60 s, 250 oC 10s, purging 10s, purging

He-2 180 s, 250 oC 60 s , 500 oC 60 s, 500 oC

He-3 180 s, 450 oC 60 s , 650 oC 60 s, 650 oC

He-4 180 s, 550 oC 90 s, 850 oC 90 s, 850 oC 200 s, 850 oC

He-5 Purging, 60 s

O2/He-1 240 s, 550 oC 30 s, 650 oC 30 s, 650 oC 30 s, 650 oC

O2/He-2 210 s, 700 oC 30 s, 750 oC 30 s, 750 oC 30 s, 750 oC

O2/He-3 210 s, 800 oC 60 s, 850 oC 60 s, 850 oC 60 s, 850 oC

O2/He-4 120 s, 940 oC 120 s, 940 oC 120 s, 940 oC

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

0%

10%

20%

30%

40%

50%

Sucrose

UST-1 HK

UST-2 HK

QD China

NJ-1China

NJ-2 China

MK HK

RU HK

TW HK

PE

C/W

SO

C

IMPROVE

NIOSH

Optimized-1

Optimized-2

low

highC loading

0%

10%

20%

30%

40%

50%

Kosan-2

Kosan-1

UST-7

Kosan-3

UST-5

UST-6

UST-3

UST-4

UST-2

QD UST-1

PE

C/T

C

IMPROVE

NIOSH

Optimized-1

Optimized-2

low

highC loading

0%

10%

20%

30%

40%

50%

60%

70%

Kosan-2

Kosan-1

UST-7

Kosan-3

UST-5

UST-6

UST-3

UST-4

UST-2

QD UST-1

PE

C/O

C

IMPROVE

NIOSH

Optimized-1

Optimized-2

Transmittance Increase before the OCEC split in the He/O2 step

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

Kosan-2

Kosan-1

UST-7

Kosan-3

UST-5

UST-6

UST-3

UST-4

UST-2

QD-1UST-1

QD-2

A1=

log

(I-i

nit

ial/I

-O2)

IMPROVE

NIOSH

Opitimized-1

Optimized-2

Smaller transmittance increase is expected with lower amount of charring.

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

-5%

0%

5%

10%

15%

20%

Kosan-2

Kosan-1

UST-7

Kosan-3

UST-5

UST-6

UST-3

UST-4

UST-2

QD UST-1

D E

C/T

C

IMPROVE

NIOSH

Optimized-1