Chemical Composition of Organic Carbon Fractions

1
Chemical Composition of Organic Carbon Fractions

• Barbara Zielinska

2
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

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ARIES Study

• 24-Hr samples were collected daily from mid-July
  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

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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.

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Monthly Means for TOR Analysis of Quartz Filters
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Extract OC
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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) .

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DCM extract
1st desorption (120 ºC)
2nd desorption (250 ºC)
3rd desorption (380 ºC)
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First Desorption, 120 C
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Second Desorption, 250 C
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Third Desorption, 380 C
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Hydrocarbons in DCM Extracts
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Correlation of Organic Carbon to Mass for DCM
Extracts
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Correlation of Organic Carbon to Mass for Acetone
Extracts
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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.

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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.

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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.