Evaluation%20of%20Secondary%20Organic%20Aerosols%20in%20Atlanta

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Evaluation of Secondary Organic Aerosols in
Atlanta Bo Yan School of Earth and
Atmospheric Sciences
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Overview

• Introduction
• Evaluation method of SOA
• Results and Discussion
• Summary

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Introduction

• Composition and sources of organic aerosols in
  fine particulate matters(PM2.5)
• Primary Organic Aerosols
• Come directly from sources as a primary
  emission. It includes n-alkanes, n-alkanoic
  acids, Polycyclic Aromatic Hydrocarbons (PAH),
  fatty acids.
• Main source wood burning, meat cooking,
  fuel combustion, road dust, vegetative detritus.
• Secondary Organic Aerosols (SOA)
• Formed in the atmosphere due to the gas
  or particle
• phase photochemical reactions. The main
  precursor of SOA is Volatile Organic Compounds
  (VOC)

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Atmospheric Process and PM2.5
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Secondary Organic Aerosols (SOA)
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Composition of Organic Aerosols in PM2.5
Source Zheng et al. 2002
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Evaluation Methods of SOA

• Organic Carbon (OC)/Elemental Carbon (EC) ratio
  approach
• Receptor models Molecular marker-based Chemical
  Mass Balance (CMB) model
• Predictive models Community Multiscale Air
  Quality modeling system (CMAQ)

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Evaluation of SOA in Atlanta using OC/EC ratio
(Cont)

• Advantages
• Simple, straightforward provided that there
  are available measurements of OC and EC.
• Disadvantages
• (OC/EC)pri is influenced by meteorology,
  diurnal and seasonal emission and local sources
  On the other hand, it is not obtained directly
  from ambient data.

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Evaluation of SOA in Atlanta using OC/EC ratio

• EC results predominantly from combustion
  sources and could be used as a tracer of primary
  OC. Because EC and primary OC often have the same
  sources and there is a representative ratio of
  primary OC/EC for a given area.
• Where, (OC)pri - estimated organic
  carbon
• (OC)sec - estimated
  secondary carbon
• EC - measured elemental
  carbon
• (OC/EC)pri - ratio of
  primary OC to EC

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Evaluation of SOA in Atlanta using OC/EC ratio
(Cont)

• How to obtain the primary OC/EC?
• Measure ambient OC/EC ratio at a special time
  when secondary organic aerosol formation is
  expected to be very low, which could be neglected
  (only primary OC exist at this time).
• The ratio could be gotten in this situation,
  where lack of sun, intermittent drizzle, low
  ozone concentration, and an unstable air mass
  suggest that photochemical activity would be
  minimum, thus secondary organic aerosol formation
  would be minimum.

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Evaluation of SOA in Atlanta using OC/EC ratio
(Cont)
Correlation between measured OC and EC for
January 2002 samples in JST
Correlation between measured OC and EC for July
2001 samples in JST
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Evaluation of SOA in Atlanta using OC/EC ratio
(Cont)
Corrected correlation between measured OC and EC
for January 2002 samples in JST
Corrected correlation between measured OC and EC
for July 2001 samples in JST
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Evaluation of SOA in Atlanta using OC/EC ratio
(Cont)

• Winter time represented by January 2002
• (OC/EC)pri2.68
• Summer time represented by July 2001
• (OC/EC)pri1.96

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Evaluation of SOA in Atlanta using OC/EC ratio
(Cont)
Concentration of Total OC and Secondary OC in
Winter Time
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Evaluation of SOA in Atlanta using OC/EC ratio
(Cont)
Concentration of Total OC and Secondary OC in
Summer Time
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Comparison of the Methods
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Summary

• Secondary Organic Aerosols are a important
  components of Organic Aerosols in PM2.5 at
  Atlanta, especially in Summer time.
• OC/EC Ratio can distinguish the secondary OC from
  total OC simply and straightforwardly.
• The method is still greatly influenced by
  meteorology, diurnal and seasonal emission, and
  local sources.
• Hourly data of OC, EC, O3 , and meteorology are
  needed to provide more insights.

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References

1. Ross Strader, et al., Atmospheric Environment
   33(1999)
2. Barbara J. Turpin, et al. Environ. Sci. Technol.
   25 (1991)
3. Ho-Jin Lim, et al. Environ. Sci. Technol. 36
   (2002)
4. Allen Robinson, et al. www.netl.doe.gov/coalpower/
   environment/ air_q/ .

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• Thanks!