Sources of Organic Aerosols Soluble in Sources of Organic Aerosols Soluble in Water in the Southeastern U.S.Water in the Southeastern U.S.

Amy P. Sullivan and R.J. WeberGeorgia Institute of Technology

Funding: NSF and NOAA

OutlineOutline• Motivation

• Brief overview of methods for water-soluble organic carbon (WSOC)– Components of PILS-TOC (On-line)– Group speciation of WSOC involving XAD-8 resin and

Size-Exclusion Chromatography (SEC) (Off-line)

• Ambient results from urban Atlanta and its surrounding regions during summer– Airborne on-line WSOC measurements– Off-line WSOC group speciation at various locations

• Summary

MotivationMotivation• Sources of organic carbon (OC) not fully known

• Using EC (elemental carbon) tracer method, suggested in Atlanta 50% of OC secondary, but can be near 90% on short time scales [Lim and Turpin, ES&T, 2002]

• Chamber studies show biogenic emissions are readily oxidized to form Secondary Organic Aerosol (SOA)

• Southeastern urban centers densely forested with coniferous trees leading to speculation that biogenic precursors major contributor to SOA

How can WSOC measurements help?How can WSOC measurements help?• SOA formation is thought to be one of the major

sources of WSOC

• Implies that methods developed for separation and analysis of WSOC could be used to investigate SOA products

Method 1: OnMethod 1: On--line Measurement of WSOCline Measurement of WSOCSchematic of PILSSchematic of PILS--TOCTOC

Drains Debubbler

Transport Liquid Flow

via syringe pumps

Drain

Vacuum PumpTeflon Filter(Background)

Valve

Activated CarbonDenuder

Particle SizeSelector

(PM1)

Liquid Filter

steam

Drain

Sievers TOC

Liquid Samplevia syringe pumps

“tee”

-Limit of Detection = 0.1 µg C/m3

-Sampling rate = 3 s

Method 2: Off-line Group Speciation of WSOC

Aerosol Organic Carbon

Water-Soluble

OC

Water-Insoluble

OCHydrophilic

Hydrophobic Recovered

Hydrophobic Unrecovered

Neutrals

Aliphatic Acids

Bases

Acids

Neutrals

Step 1XAD-8

Step 2SEC

-Analysis performed on Hi-Volume integrated filters

XAD-8 Calibration (based on 36 standards)

Mono-, Di-,Oxocarboxylic Aliphatic Acids

Carbonyls

Saccharides

Amines

Aromatics

Cyclic Acids

Organic Nitrates

HydrophilicRecovered

HydrophobicUnrecovered Hydrophobic

Carbons < 4Carbons < 4 Carbons > 4Carbons > 4

Carbons < 4Carbons < 4 Carbons > 4Carbons > 4

XX

XX

XX

XX

XX

100% Penetration 0% Penetration

Modified SEC Method

20x10-3

15

10

5

0

Con

cent

ratio

n (p

pb C

)

00:20 00:25 00:30 00:35 00:40 00:45 00:50 00:55Tr (min)

HYDROPHILICBASES

HYDROPHILICNEUTRALS

HYDROPHILICALIPHATIC

ACIDS

C2 - diacid

C3 - diacidlevoglucosan

ethanolamine

Hydrophilic Calibration

-By not adjusting ionic strength and buffering sample (pH 6.8) obtain separation by functional groups

Total Organic Carbon Analyzer

SEC

WSOC, Hydrophilic, or Recovered Hydrophobic

Sample

ICARTT:ITCT 2004

55

50

45

40

35

Latit

ude

(deg

rees

)

-85 -80 -75 -70 -65 -60 -55Longitude (degrees)

Non-Biomass Surface Source WSOC versus CO

10

8

6

4

2

0

WS

OC

(µg

C/m

3 )

300250200150100CO (ppbv)

y = -2.2±0.08 + 0.03x±0.01 R2 = 0.53

New York City PlumeAll Data

(acetonitrile < 200 pptv and altitude < 2 km)

-WSOC-CO R2 = 0.53, fairly well correlated

-WSOC-CO R2 = 0.82, highly correlated in specific urban plumes

CO: J.S. Holloway, NOAA-ESRL/CIRESAcetonitrile: J.A. de Gouw and C. Warneke, NOAA-ESRL/CIRES

8

6

4

2

0

WSO

C (µ

g C

/m3 )

16:25 16:30 16:35 16:40 16:45Time (UTC)

240

200

160

120

CO

(ppbv)

800

600

400

200

0

Altit

ude

(m)

WSOC

CO

WSOC Evolution in Urban Plumes-Back trajectories of WSOC plumes that intercepted NYC

∆WSOC/∆CO• Lowest near city• Begins to level off after ~ 1 day to 32 ± 4 (µg C/m3)/ppmv•WSOC produced from compounds co-emitted with CO•Urban emissions rapidly converted to secondary products?

45

44

43

42

41

40

39

38

Latit

ude

(deg

rees

)

-80 -75 -70 -65 -60Longitude (degrees)

0720A0720B

0721A

0721B

0814A0814A'

0814B'0814B

35

30

25

20

15

10

5

0∆WSO

C/∆

CO

((µg

C/m

3 )/ppm

v)

35302520151050Advection Time from Urban Center (hours)

0720A

0720B

0721A0721B

0814A

0814A'

0814B'

0814B

Atlanta Flyby

-WSOC-CO R2 = 0.83(excluding in-cloud)-WSOC doesn’t track in fresher CO plumes

-Wide spread elevated CO and WSOC in boundary layer

-∆WSOC/∆CO ~33 ± 5 (µg C/m3)/ppmv, similar to NYC (32 ± 4)

6

5

4

3

2

1

0

WSO

C (µg

C/m

3 )

18:0 0 1 8:30 19:00 19:30 20:0 0Tim e (UTC)

2 00

1 80

1 60

1 40

1 20

1 00

8 0

CO

(ppbv)

5 0004 0003 0002 0001 000

0Altit

ude

(m)

CO

WSOC

A

Aircraft directlyover Atlanta

B

C

D

E

CloudPenetration

Yorkville, GA~80 km west of GIT

(during period of poor air quality)

Georgia Institute of Technology (GIT)Roof top of ES&T Building

Next to I-75/85~400 m from GIT and~1 m from highway

Sampling SitesSampling Sitesfor WSOC Group for WSOC Group

SpeciationSpeciation

Hi-Volume Samplers: B. Yan and M. Zheng, Georgia Institute of Technology

400 m

From: http://maps.google.com/

GIT vs. Highway GIT vs. Yorkville

400 m

80 km

Carbonaceous Aerosol ComparisonSite EC

(µg C/m3)OC

(µg C/m3)WSOC

(µg C/m3)

HighwayGITGIT

4.430.480.48

10.827.837.83

4.734.334.33

YorkvilleGITGIT

0.150.900.90

8.5110.5010.50

6.266.726.72

WSOC OC

0.440.550.55

0.740.640.64

Results from 2 separate paired experiments

Carbonaceous Aerosol Comparison

-EC = primary•Highest by highway (GIT vs. Highway)•Highest in urban center (GIT vs. Yorkville)

Site EC(µg C/m3)

OC(µg C/m3)

WSOC(µg C/m3)

HighwayGITGIT

4.430.480.48

10.827.837.83

4.734.334.33

YorkvilleGITGIT

0.150.900.90

8.5110.5010.50

6.266.726.72

WSOC OC

0.440.550.55

0.740.640.64

Carbonaceous Aerosol Comparison

-OC = primary and secondary, less difference

Site EC(µg C/m3)

OC(µg C/m3)

WSOC(µg C/m3)

HighwayGITGIT

4.430.480.48

10.827.837.83

4.734.334.33

YorkvilleGITGIT

0.150.900.90

8.5110.5010.50

6.266.726.72

WSOC OC

0.440.550.55

0.740.640.64

Carbonaceous Aerosol Comparison

-WSOC little variability-Most compounds comprising WSOC not directly from mobile sources (NOT PRIMARY)

Site EC(µg C/m3)

OC(µg C/m3)

WSOC(µg C/m3)

HighwayGITGIT

4.430.480.48

10.827.837.83

4.734.334.33

YorkvilleGITGIT

0.150.900.90

8.5110.5010.50

6.266.726.72

WSOC OC

0.440.550.55

0.740.640.64

Carbonaceous Aerosol Comparison

-Higher ratio further from mobile sources due to smaller influence from primary emissions and driven more by spatial variability of primary OC

Site EC(µg C/m3)

OC(µg C/m3)

WSOC(µg C/m3)

HighwayGITGIT

4.430.480.48

10.827.837.83

4.734.334.33

YorkvilleGITGIT

0.150.900.90

8.5110.5010.50

6.266.726.72

WSOC OC

0.440.550.55

0.740.640.64

36%

21%1%

15%

6%

1%

9%

11%

Three Main Chemical Components of WSOC

1.Hydrophilic aliphatic acids, e.g., C < 4 acids2.Hydrophilic neutrals, e.g. saccharides and C< 4

carbonyls3.Recovered hydrophobic acids, e.g. aromatic acids

or compounds with similar properties

Includes expected biogenic SOA products

GIT 2005during PM Event

WSOC/OC = 0.641

23

Correlations of Three Main WSOC fractions(all data)

-Hydrophilic aliphatic acids and neutrals and recovered hydrophobic acids all correlated, near-zero intercepts-Suggests their sources are all linked

2.0

1.5

1.0

0.5

0.0

1.20.80.40.0

R2 = 0.81

YorkvilleGIT 2005GIT 2004 Highway

3.0

2.5

2.0

1.5

1.0

0.5

0.0

2.01.51.00.50.0

R2 = 0.87

1 vs. 2 1 vs. 3 2 vs. 33.0

2.5

2.0

1.5

1.0

0.5

0.0

1.21.00.80.60.40.20.0

R2= 0.79

Mass Balance on Measured VOCs andMass Balance on Measured VOCs andOC (POM) from NEAQS 2002OC (POM) from NEAQS 2002

Secondary

Primary VOCs

Alkanes largest -∆mass

From: J.A. de Gouw et al., JGR, 2005

-SOA: little evidence for biogenic, not explained by aromatic VOCs

SummarySummary• In summer urban Atlanta and its surrounding areas

WSOC has a regional characteristic and its source appears to be largely SOA– Spatially uniform compared to primary particles (e.g., EC),

thus likely not primary

• No clear evidence for strong biogenic SOA signal, instead points to precursors from mobile sources– Supported by:

• High WSOC-CO correlations on large spatial scale• Similar ∆WSOC/∆CO in Atlanta and NYC• Known biogenic products small fraction of WSOC

• Summer WSOC composition:1. Hydrophilic aliphatic acids2. Hydrophilic neutrals3. Recovered hydrophobic acids-All correlated suggesting linked sources

• Implication that mobile source emissions may play a large role in the formation of WSOC in urban regions in the southeastern U.S.

• For more details on WSOC group speciation methods see poster A33B-0876 on Wed. afternoon