what are the important parameters that need to be defined for a carbonaceous aerosol analysis ?

What are the important parameters that need to

be defined for a carbonaceous aerosol

analysis ?

Hélène CACHIER

Laboratoire des Sciences du Climat et de l’Environnement

Laboratoire des Sciences du Climat et de l ’Environnement Durando ECOC workshop, March 2003

How should these be documented for

different analysis protocols ?

Carbonaceous Combustion Aerosols

Physical and chemical diversity: their own story

due to their origin source

due to the atmospheric environment

due to their age


Carbonaceous Combustion Aerosolsmorphology

porous fly ash (carbonaceous)


diesel microsoots

Courtesy of A. Lefèvre

Carbonaceous Combustion Aerosolsmorphology

fresh diesel microsoots


Biomass burning particles

Courtesy of A. Gaudichet


Atmospheric aging



Chemical complexity of EC (BC) and OC


From D. Smith et al., 1989

Difficult to find a chemical separation

Difficult to find a thermal separation

Fate of attached VOC?


Chemical complexity of the aerosol mix


Biomass burning aerosols (savanna fires)

Carbonaceous Combustion AerosolsChemical complexity of the aerosol mix


Weekly samples from Finokalia (Crete) nov 01-jun02

What type of method to be used?


2-step thermal method (Oxygen) : « blind » method

TOA under Oxygen : better

TOA under He and He/O2:

Pyrolysis vs Combustion: don’t mix

11TO

T

10TO

T

11bT

OT

12TO

T

12TO

T

11TO

T

10TO

T

11bT

OT

13TO

R

13TO

R

I

Interlaboratory comparisonsAre not consistent

Discrepancy is sample dependent

Schmid et al, 2001

What to avoid ?


Interferences with other species: carbonates dusts salts (K)

Charring of the Organic Component

Overlap of the 2 EC and OC components:

Value of optical correction ?

Untimely removal of EC

TOA / Oxygen


Charring minimized

Role of K (Na)

Carbonates : no problem? Temperature max?

Plateau temperature and duration ?

Negative role of concentration loading?

Temperature steps Optical (laser transmission) measurement

C peaks Calibration

Limit OC/EC

2 -step TOA example


OC1 OC2 OC3 OC4 OP EC

2- Step TOA He/He-Ox


Peak (fraction) resolution BUT Important charring

role of plateau temperaturerole of plateau durationrole of concentration loadingrole of inorganic salt

Untimely departure of EC (negative artefact)

Refractory OC (positive artefact) temperature of the last OC plateau

Reflectance or Transmittance ? role of concentration loadingrole of filter matrix


From Chow et al.,2001

First type of 2-step TOA


From Chow et al.2001

Second type of 2-step TOA

Thermograms of levoglucosan in the (a) absence and in the (b) presence of ammonium

bisulfate using the UST-2 thermal method


Thermal evolution of Organic species altered by inorganic species

Yu et al., 2002

!!! use of standard


Yu et al., 2002

An important part of the charred OC(PEC) is from water soluble aerosol

Use aerosol water extract as PEC surrogate

Thermograms of a same aerosol water extract using (a) the NIOSH and (b) the

UST-3 thermal methods.

Prolonging the duration at each temperature step reduces charring


Yu et al., 2002

Hypothetic thermograms of pure PEC, pure NEC, and a mixture of the two in a HeO2 atmosphere


Charring corrections primarily rely on the hypothesis that charred carbon (PEC) evolves prior to EC (Native EC NEC)

Charred OC (PEC) does not evolve

prior to EC (NEC)b


Thermograms of (a) an untreated aerosol sample and its water extract and (b) charcoal

Nor do PEC and NEC have

the same absorption coefficient

From Yang and Yu, 2002

0

100

200

300

400

500

600

700

800

900

1000

0 100 200 300 400 500 600 700Time, s

Tem

p., °

C

FID

, Las

er T

rans

(rela

tive

units

)

TempLaser TransFID

100% He 2% O2 + 98%He

OC1 OC2 OC3 OC4 EC1 EC2 EC3 EC4 EC50

100

200

300

400

500

600

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800

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1000

0 100 200 300 400 500 600 700Time, s

Tem

p., °

C

FID

, Las

er T

rans

(rela

tive

units

)

TempLaser TransFID

100% He 2% O2 + 98%He

OC1 OC2 OC3 OC4 EC1 EC2 EC3 EC4 EC5

Analysis of a « dust» sample by the Niosh method


Whitening of the filter sample



RecommendationsReduce charring correction uncertainty:

reduce charring by increasing plateau durationreduce charring of the high temperature plateauincrease the resolution around the OC/EC split point

Avoid interactions with dusts (iron oxides)Proceed to removal of carbonates prior to analysis if necessary

Avoid untimely departure of EC during the He step

Need to find an experimental design to evaluate if OC remains on sample after the He step of the thermal procedure

Define an acceptable concentration range (gC/cm2)

charring cannot be predefined

0,0

0,5

1,0

1,5

2,0

2,5

3,0

BC

, µgC

/m3

0

2

4

6

8

10

12

14

16

nss-

SO

4, µ

g/m

3

BC, Thermal methodnss-SO4

0,0

0,5

1,0

1,5

2,0

2,5

3,0

25/07 30/07 04/08 09/08 14/08 19/08 24/08

BC

, µgC

/m3

0,0

0,3

0,5

0,8

1,0

1,3

1,5

nss-

K, µ

g/m

3

BC, IMPROVE Tempprogramnss-K


Analysis of Crete samples Minos experiment, Aug 2001

Why does the DRI-Improve mebbhod insensitive to «industrial» BC?

Why is it very sensitive to Biomass Burning BC?

From Sciare et al., 2003

Analysis of impactor samples

Heterogeneity of the depositConcentration of particles on small areas

Role of the substrate (quartz vs aluminium)



Are you really wanting to change your own protocole??

what are the important parameters that need to be defined for a carbonaceous aerosol analysis ?

Documents

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