Transcript Organic Carbon Fraction Composition

Chemical Composition of
Organic Carbon Fractions
Barbara Zielinska
Study:
ARIES: chemical characterization of
atmospheric aerosol in support of
Atlanta (Georgia) health study.
Our goal: to provide information related
to fine particle and semi-volatile organic
carbon concentrations and composition
ARIES Study:
24-Hr samples were collected daily from midJuly 1998 to end of December 1999, at a
residential/industrial site in Atlanta, Georgia
(Jefferson Street)
DRI Sequential Fine Particle/SVOC Sampler
with 2.5 µm inlet and flow rate 113 L/min
Quartz filters (10 cm) followed by
PUF/XAD/PUF cartridges
Sample Extraction and Analysis:
0.5 cm2 punch from the filter was analyzed for
OC and EC by thermal/optical reflectance
(TOR) method.
Samples (filters and PUF/XAD/PUF) were
extracted with DCM followed by acetone and
then by water by microwave extraction.
Aliquot of each extract (~20 µl) was deposited
on a pre-fired quartz filter punch and the
solvent was evaporated to a constant weight.
Quartz punches were analyzed by TOR method
for OC/EC.
Monthly Means for TOR Analysis of
Quartz Filters
12
10
OC
6
EC
4
2
June
May
April
March
Feb
Jan
Decem
Novem
Octob
Sept
August
0
July
ug/m3
8
filt_oc
dcm_oc
ace_oc
h2o_oc
12/28/98
12/24/98
12/20/98
12/16/98
12/12/98
12/8/98
12/4/98
11/30/98
11/26/98
11/22/98
11/18/98
11/14/98
11/10/98
11/6/98
11/2/98
10/29/98
10/25/98
10/21/98
10/17/98
10/13/98
10/9/98
10/5/98
10/1/98
9/27/98
9/23/98
ug/m3
Extract OC
30
25
20
15
10
5
0
Organic Composition of Extracts
Select extracts were analyzed by gas
chromatography/mass spectrometry (GC/MS)
using a thermal desorption method.
Thermal desporption was conducted in
sequential fashion with increasing
temperatures that mimic the temperature
ramps used with the TOR method (1: 120 ºC;
2: 250 ºC; 3: 380 ºC) .
DCM extract
1st desorption (120 ºC)
2nd desorption (250 ºC)
3rd desorption (380 ºC)
First Desorption, 120 °C
Second Desorption, 250 °C
Third Desorption, 380 °C
Hydrocarbons in DCM Extracts
Correlation of Organic Carbon to Mass for
DCM Extracts
DCM - Filter/PUF, OC/Mass
90
80
60
50
40
y = 1.6728x + 0.4523
R2 = 0.883
30
20
10
0
0
10
20
30
40
50
DCM - Filter, OC/Mass
8
OC (ug/m3)
Mass (ug/m3)
Mass (ug/m3)
70
6
4
y = 1.4619x + 1.4825
R2 = 0.792
2
0
0
1
2
3
OC (ug/m3)
4
5
Correlation of Organic Carbon to Mass for
Acetone Extracts
180
160
140
120
100
80
60
40
20
0
y = 2.0491x - 0.0797
R2 = 0.8899
0
20
40
60
80
100Acetone - Filter, OC/Mass
OC (ug/m3)
35
30
Mass (ug/m3)
Mass (ug/m3)
Acetone - Filter/PUF, OC/Mass
25
20
y = 2.5165x - 0.6641
R2 = 0.9428
15
10
5
0
0
2
4
6
8
OC (ug/m3)
10
12
14
Conclusions:
Sequential extraction of fine particle samples showed
that most of the organic carbon is distributed
between the DCM and acetone extracts. It is
possible that many of the compounds that could be
extracted with water are extracted in the first two
solvents.
Sequential thermal desorption of a DCM extract onto
a GC/MS showed a series of non-polar compounds of
increasing volatility.
The desorption method can provide an insight into
the composition of the organic fractions observed
during the TOR temperature ramps.
Conclusions, cont.
Thermal desorption analysis of the acetone extracts
would require some derivitization method to aid in
the analysis of polar compounds that are present in
the acetone and water fractions.
The relationship between PM2.5 mass and organic
carbon for DCM and acetone extracts yields slopes
that is slightly higher than current estimates of
correction factors that should be applied to organic
carbon numbers derived from the TOR method.
A higher slope is observed for acetone, which is a
higher polarity solvent and contains more oxygenated
compounds.
Acknowledgements
The author would like to thank Electric Power
Research Institute (EPRI Project Manager –
presently Dr. Alan Hanson, formerly Dr. Tina
Bahadori ) for the financial support of this
work. Mr. Eric Edgerton (ARA, Inc.) is
thanked for sample collection and Dr. Tina
Bahadori for her continuous interest and
encouragement.