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

2. Overview Introduction Evaluation method of SOA Results and Discussion
Summary

3. 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)

4. Atmospheric Process and PM2.5

5. Secondary Organic Aerosols (SOA)

6. Composition of Organic Aerosols in PM2.5
Source: Zheng et al. 2002

7. 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)

8. Evaluation of SOA in Atlanta using OC/EC ratio (Con’t)
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.

9. 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

10. Evaluation of SOA in Atlanta using OC/EC ratio (Con’t)
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.

11. Evaluation of SOA in Atlanta using OC/EC ratio (Con’t)
Correlation between measured OC and EC for January 2002 samples in JST
Correlation between measured OC and EC for July 2001 samples in JST

12. Evaluation of SOA in Atlanta using OC/EC ratio (Con’t)
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

13. Evaluation of SOA in Atlanta using OC/EC ratio (Con’t)
Winter time represented by January 2002
(OC/EC)pri=2.68
Summer time represented by July 2001
(OC/EC)pri=1.96

14. Evaluation of SOA in Atlanta using OC/EC ratio (Con’t)
Concentration of Total OC and Secondary OC in Winter Time

15. Evaluation of SOA in Atlanta using OC/EC ratio (Con’t)
Concentration of Total OC and Secondary OC in Summer Time

16. Comparison of the Methods

17. 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.

18. References Ross Strader, et al., Atmospheric Environment 33(1999);
Barbara J. Turpin, et al. Environ. Sci. Technol. 25 (1991);
Ho-Jin Lim, et al. Environ. Sci. Technol. 36 (2002);
Allen Robinson, et al. air_q/ .

19. Thanks!