evaluation of secondary organic aerosols in atlanta bo yan

Evaluation of Secondary Organic Aerosols in Atlanta

Bo Yan

School of Earth and Atmospheric Sciences

Overview

Introduction Evaluation method of SOA Results and Discussion Summary

Introduction

Composition and sources of organic aerosols in fine particulate matters(PM2.5)

1. 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.

2. 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)

Atmospheric Process and PM2.5

Secondary Organic Aerosols (SOA)

Composition of Organic Aerosols in PM2.5

Source: Zheng et al. 2002

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)

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.

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

pripri (OC/EC)(EC)(OC)

pritotsec (OC)(OC)(OC)


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.


y = 2.61x + 0.65

R2 = 0.82

0

2

4

6

8

10

12

0 1 2 3 4

Elemental Carbon (ug/cm3)

Org

an

ic C

arb

on

(u

g/c

m3

)

y = 1.97x + 1.01

R2 = 0.63

0

1

2

3

4

5

6

7

8

9

0 0.5 1 1.5 2 2.5 3 3.5


Org

an

ic C

arb

on

(u

g/c

m3

)

Correlation between measured OC and EC for January 2002 samples in JST

Correlation between measured OC and EC for July 2001 samples in JST


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

y = 1.96x + 0.76

R2 = 0.78

0

1

2

3

4

5

6

7

8

0 0.5 1 1.5 2 2.5 3 3.5


Org

anic

Car

bon

(ug/

cm3)

y = 2.68x + 0.49

R2 = 0.82

0

2

4

6

8

10

12

0 1 2 3 4

Elemantal Carbon (ug/cm3)

Org

an

ic C

arb

on

(u

g/c

m3

)


Winter time represented by January 2002

(OC/EC)pri=2.68

Summer time represented by July 2001 (OC/EC)pri=1.96


0

2

4

6

8

10

12

1/1/

02

1/3/

02

1/5/

02

1/7/

02

1/9/

02

1/11

/02

1/13

/02

1/15

/02

1/17

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1/19

/02

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/02

1/23

/02

1/25

/02

1/27

/02

1/29

/02

1/31

/02

Co

nc

en

tra

tio

n (

ug

/cm

3)

Total OC

Secondary OC

Concentration of Total OC and Secondary OC in Winter Time


Concentration of Total OC and Secondary OC in Summer Time

0

1

2

3

4

5

6

7

8

9

7/1/

01

7/3/

01

7/5/

01

7/7/

01

7/9/

01

7/11

/01

7/13

/01

7/15

/01

7/17

/01

7/19

/01

7/21

/01

7/23

/01

7/25

/01

7/27

/01

7/29

/01

7/31

/01

Co

nc

en

tra

tio

n (

ug

/cm

3)

Total OC

Secondary OC

Comparison of the Methods

0

0.5

1

1.5

2

2.5

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3.5

4

1/1/

02

1/3/

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1/31

/02

Co

nc

en

tra

tio

n (

ug

/cm

3) OC/EC

CMB

CMAQ

0

1

2

3

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7

7/1/

01

7/3/

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7/5/

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7/7/

01

7/9/

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7/11

/01

7/13

/01

7/15

/01

7/17

/01

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/01

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/01

7/23

/01

7/25

/01

7/27

/01

7/29

/01

7/31

/01

Co

nc

en

tra

tio

n (

ug

/cm

3) OC/EC

CMB

CMAQ

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.

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/ .

Thanks!

evaluation of secondary organic aerosols in atlanta bo yan

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