Tadeusz E. Kleindienst 1, Edward O. Edney 1, Michael Lewandowski 1,John H. Offenberg 1, and Mohammed Jaoui 2

1 National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina USA

2 Alion Science and Technology, Research Triangle Park, North Carolina USA

Contribution of SOA to Ambient PM2.5 Organic Carbon in Eastern United States Locations

MANE-VU/Midwest RPO Regional Haze Science MeetingBaltimore, Maryland

July 10, 2007

Background• Condensable material formed from gas-phase reactions of

hydrocarbons produce secondary organic aerosol (SOA) that comprises part of the organic carbon (OC) in PM2.5.

• SOA typically contains organic compounds more highly polar than those from primary emissions and can be semivolatile or nonvolatile.

• Recent data indicates SOA can be a significant summer component of PM2.5 in the eastern U.S.

• Laboratory experiments indicate that organic products in field samples can be associated with specific hydrocarbon precursors (Edney et al. Atmos. Environ., 2003).

• Organic tracer technique for SOA has recently been described (Kleindienst et al., Atmos. Environ., in press)

Other Approaches for Evaluating Ambient SOA(SOA/OC)

● Deficit in chemical mass balance between measured OC and primary organic aerosol (POA) from CMB analysis

(Schauer et al., 2002; Zheng et al., 2002)

● Contribution of SOA to PM2.5 from OC/EC ratio(Turpin and Huntzicker 1995)

● Relative contributions of anthropogenic and biogenic HCs to SOA based on a combined 14C and source-receptor method

(e.g. Lewis et al., 2004)

Simplified View of Ambient Primary and Secondary Carbon

Organic Aerosol Component of PM

PrimarySources

SecondarySources

Distribution of Source Contributions Changes with Season

General Description of SOA from Individual Source

Tracercompounds

Polar multifunctional oxygenates that may include oligomers and other high

molecular-weight compounds

SOA component from α-pinene reactions with OH, O3, NO3 followed

by secondary and higher order aerosol-forming processes

α-P SOA

Objectives for the Study• Find tracer compounds representative of the major SOA precursors from laboratory studies.

Identify tracer compounds found both in the laboratory and field.Estimate the mass fraction of tracers to the formed SOAFocus on isoprene, α-pinene, β-caryophyllene, toluene

• Determine major sources of SOA in PM2.5 in RTP, NC, Detroit, MI, and other locations using the tracer compounds.

• What fraction of the OC represented by SOC.

• Compare biogenic vs. anthropogenic contribution.

• Examine seasonal dependencies.

• Compare differences in location using the same analysis.

NERL Dynamic Photochemical Reaction Simulator

Volume = 14.5 m3

40 L min-1 (τ = 6 h)

Ozone, SO2 and NO/NOx

Analyzers

Scanning Mobility Particle Sizer

(SMPS)

Hygrometer

Inlet Manifold

Gas Chromatography -Flame Ionization

Detector (GC-FID)Other Sampling

Gas Phase Carbonyl Product Measurements

Chemical Composition

LC-ESI ESIMALDIIC

Inorganic

Mass Measurement

Gravimetric Mass

Experimental System for Laboratory Studies

• Experiments conducted in a dynamic mode to operate at relatively low reactant concentrations and to collect sufficient aerosol for analysis.

• Analyze tracer compounds by GC/ITMS and OA and OC by standard methods.

Organic

GC-MS

SemicontinuousOrganic Carbon

MeasurementFilter Sampling

Devices forChamber Aerosol

SOCMsmt

SOAMsmt

Reactive Systems Contributing to SOA Studied Here

Isoprene PhotooxidationRole of acid catalysis (H2SO4 acidic seed; in presence of SO2)

α-Pinene OxidationPhotooxidationOzone reactionRole of acid catalysis

Toluene Photooxidation

β-Caryophyllene OxidationPhotooxidationOzone reaction

Tracer Compounds from Laboratory Irradiations

Tracer Compounds for the Source Categories

Isoprene SOA Tracers2-Methylglyceric acid

2-Methylerythritol

2-Methylthreitol

Toluene SOA Tracer2,3-Dihydroxy-4-oxopentanoic acid

β-Caryophyllene SOA Tracerβ-Caryophyllinic acid (C14H22O4)

α-Pinene SOA TracersPinic acid

Pinonic acid

3-Acetyl pentanedioic acid

3-Acetyl hexanedioic acid

3-(2-Hydroxyethyl)-2,2-dimethylcyclo-butane carboxylic acid

3-Hydroxyglutaric acid

2-Hydroxy-4-isopropyladipic acid

3-Hydroxy-4,4-dimethylglutaric acid

Structures for Selected Tracer Compounds

A–3

OOH

O

HOPinicacid

OHHO

O O OA–2

H O

O O

O H

OA–4

A–5

A–6

I–1

I–2

I–3

C–1

Pinonicacid

α-Pinene tracers

Isoprene tracers

Toluene tracer

β-Caryophyllene tracer

T–3

Laboratory Data for Mass Fractions(e.g., α-pinene photooxidation; OM/OCα-p = 1.37 ± 0.15)

Experiment ID [hco] (ppmC)

[NOX,o](ppm)

[SOA](μg m-3)

Σ [tri](μg m-3) f soa

α-p – 1 2.18 0.186 111.6 10.3 0.092

α-p – 2 4.18 0.450 74.2 11.9 0.160

α-p – 3 4.18 0.450 86.7 12.9 0.148

α-p – 4 2.19 0.272 72.0 5.8 0.081

α-p – 5 2.19 0.250 101.3 31 0.306

α-p – 6 3.13 0.317 128.0 16.7 0.130

α-p – 7 4.95 0.494 333.8 79.3 0.237

α-p – 8 5.27 0.490 298.3 39.4 0.132

α-p – 9 5.27 0.490 271.0 49.1 0.181

α-p – 10 2.43 0.307 80.9 29.8 0.368

α-p – 11 2.28 0.307 269.0 30.6 0.114

α-p – 12 2.32 0.279 65.4 10.3 0.157

α-p – 13 3.97 0.279 165.0 18.9 0.115

α-p – 14 1.04 0.409 9.7 0.99 0.102

α-p – 15 2.20 0.420 102 19.7 0.193

average f soa, α-p 0.168 ± 0.081

average f soc, α-p 0.231 ± 0.111

Research Triangle Park, NC* Summer 2000, 2001

Baltimore, MD* Summer 2001

Philadelphia, PA (NEOPS)* Summer 2001

New York, NY* Summer 2001

Tampa, FL (BRACE) Summer 2002

Research Triangle Park, NC Entire Year 2003

Detroit, MI (DEARS) Summer 2004, 2005

Detroit, MI (DEARS) Winter

PM2.5 Field Measurements

* Qualitative measurements with double derivative, PFBHA/BSTFA

Example of Tracer Compounds from TIC(Detroit, MI, 24 Aug 2004; OC = 3.72 μg m-3)

Sum of Tracer Concentrations as KPAI : Isoprene: 168 ng m-3

A: α-Pinene: 153 ng m-3

B: β-Caryophyllene: 6.8 ng m-3

T : Toluene: 4.4 ng m-3

Relative Abundance of Tracer Compounds in RTP, NC 2003

• Laboratory measurementsIrradiated single component hydrocarbon/NOX mixtures; repeat for other conditionsIdentify tracer compounds and determine concentrations as ketopinic acid Calculate the mass fraction of the tracer compounds to the measured SOC

• Apply to field measurementsMeasure SOC tracers in ambient PM2.5

Apply the mass fraction factor to get the SOC for each precursor typeCompare SOC contributions to the measured OC

• Assumptions and uncertaintiesAssume mass fraction of the tracers is the same in the field as in the laboratory.Other possible of sources of the tracer compounds currently not knownStandard deviation of the mass fraction measurements were on average 35%Extrapolations from single hydrocarbon contributions to compound classes.

• Measurement of ambient OC and the precursor contribution to OC are independent quantities.

Method for Estimating SOC Source Contributions

Contribution of Isoprene SOC to Ambient OC(Using 2-methylglyceric acid and two 2-methyl tetrols; 2003 - RTP, NC USA)

0

1

2

3

4

5

6

7

812 20 27 27 31 41 45 48 55 69 83 90 10

5

118

132

153

160

174

176

209

216

230

237

239

245

253

262

265

279

293

304

321

324

342

363

Julian Date - 2003

ugC

m-3

OCisoprene

Winter Spring Summer Fall

Contribution of Monoterpene SOC to Ambient OC(Nine tracers for α-pinene; 2003 - RTP, NC USA)

0

1

2

3

4

5

6

7

812 20 27 27 31 41 45 48 55 69 83 90 10

5

118

132

153

160

174

176

209

216

230

237

239

245

253

262

265

279

293

304

321

324

342

363

Julian Date - 2003

ugC

m-3

OCa-pinene

Winter Spring Summer Fall

Contribution of Sesquiterpene SOC to Ambient OC(Tracer using β-caryophyllinic acid; 2003 - RTP, NC USA)

0

1

2

3

4

5

6

7

8

12 20 27 27 31 41 45 48 55 69 83 90 105

118

132

153

160

174

176

209

216

230

237

239

245

253

262

265

279

293

304

321

324

342

363

Julian Date - 2003

ugC

m-3

OCb-caryophyllene

Winter Spring Summer Fall

Contribution of Aromatic SOC to Ambient OC(Tracer using 2,3-dihydroxy-4-oxopentanoic acid; 2003 - RTP, NC USA)

0

1

2

3

4

5

6

7

8

12 20 27 27 31 41 45 48 55 69 83 90 105

118

132

153

160

174

176

209

216

230

237

239

245

253

262

265

279

293

304

321

324

342

363

Julian Date - 2003

ugC

m-3

OCtoluene

Winter Spring Summer Fall

0

1

2

3

4

5

6

7

812 20 27 27 31 41 45 48 55 69 83 90 105

118

132

153

160

174

176

209

216

230

237

239

245

253

262

265

279

293

304

321

324

342

363

Julian Date 2003

ug C

m-3

othertolueneb-caryophylleneisoprenea-pinene

SOC Contributions to Ambient OC(2003 – Research Triangle Park, NC)

Winter Spring Summer Fall

Bimonthly Contribution of SOC to Ambient OC(2003 Research Triangle Park, NC)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Jan-Feb March-April May-June July-August Sept-Oct Nov-Dec

OC

Con

tribu

tions

(ug/

m3)

Isoprene a-Pinene b-Caryophyllene Toluene Other OC

0.21

0.36

0.44

estimated fraction SOC0.68

0.41

0.28

Other OC = OC - Isoprene SOA - Aromatic SOA - Monoterpene SOA - Sesquiterpene SOA

Other OC includes biomass comb, gasoline exhaust, diesel emissions and meat cooking operations

SOC Contributions to Ambient OC(DEARS Ambassador Bridge Site, Detroit, MI, 11 Aug – 1 Sep 2004)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Sample

Org

anic

Car

bon

(ugC

/m3)

Isoprene a-pinene b-Caryophyllene Toluene Other

Avg SOC mass: 1.55 μgC m-3

Avg fraction SOC: 0.474Anthrop SOC/Total SOC: 0.13

Summary of Key Points

• Secondary organic aerosol from isoprene, monoterpenes, sesquiterpenes, and aromatics contributes substantially to organic carbon in PM2.5 in the eastern U.S. mainly during the summer. Other U.S. areas under study.

• Aromatic contribution higher than typically predicated in air quality models.

• Organic carbon in PM2.5 was found to range from 2 – 5 μgC m-3 throughout the year with primary sources dominating in the winter and SOC dominating during the summer. Primary and secondary contributions can be offsetting leading to minor seasonal trends.

• Estimates of SOC contribution from biogenic HC precursors found to be substantially greater than anthropogenic HC precursors in the eastern U.S.

• Results consistent with SOC contributions to the organic carbon measured in laboratory mixtures and with 14C data measured in laboratory experiments and from 14C in field studies.

Next Steps• Conduct studies combining both CMB analysis for primary compounds

and mass fractions for secondary compounds to see the degree of consistency between SOA and “other OC” from the CMB analysis.

• Look at alternative double derivative technique to improve sensitivity of tracers from aromatic hydrocarbons.

• Use information from laboratory and field studies to provide basis for an improved SOA module for CMAQ.

• Determine tracers compounds from other classes of possible SOA producing hydrocarbons, such as, high MW alkanes, etc.

• Determine tracer compounds from additional high volume aromatic hydrocarbons (e.g., m-xylene, 1,2,4-TMB) and sesquiterpenes (e.g., α-humulene, α-farnesene).

• Examine SOA production from complex mixtures.

• Further study role of acid-catalysis on SOA formation and possible tracer compounds produced.

Bibliography• Edney et al., 2003, Polar organic oxygenates in PM2.5 at a southeastern site in the United States, Atmos. Environ. 37,

3947-3965.

• Kleindienst et al., 2004, Determination of secondary organic aerosol products from the photooxidation of toluene and their implications in PM2.5. J. Atmos. Chem. 47, 79-100.

• Jaoui et al, 2004, Identification and quantification of aerosol polar oxygenated compounds bearing carboxylic or hydroxyl groups. 1. Method development. Analyt. Chem. 76, 4765-4778.

• Jaoui et al., 2005, Identification and quantification of aerosol polar oxygenated compounds bearing carboxylic or hydroxyl groups. 2. Organic tracer compounds from monoterpenes, Environ. Sci. Tech. 39, 5661-5673.

• Edney et al., 2005, Formation of 2-methyl tetrols and 2-methylglyceric acid in secondary organic aerosol from laboratory irradiated isoprene/NOX/SO2/air mixtures and their detection in ambient PM2.5 samples collected in the eastern United States, Atmos. Environ. 39, 5281-5289.

• Offenberg et al. 2006, Thermal properties of secondary organic aerosols. Geophys. Res. Lett. 33, L03816

• Claeys et al. 2007, Hydroxydicarboxylic acids: Markers for secondary organic aerosol from the photooxidation of α-pinene. Environ. Sci. Technol. 41, 1628-1634.

• Jaoui et al., 2007, β-caryophyllinic acid: An atmospheric tracer for β-caryophyllene secondary organic aerosol. Geophys. Res. Lett. 34, L05816.

• Surratt et al. 2007, Evidence for organosulfates in secondary organic aerosol. Environ. Sci. Technol. 41, 517-527.

• Lewandowski et al., 2007, Composition of PM2.5 during the summer of 2003 in Research Triangle Park, North Carolina. Atmos. Environ. 47, 4073-4083.

• Offenberg et al. 2007, Contributions of toluene and α-pinene to SOA formed in an irradiated toluene/α-pinene/NOX/air mixture: Comparison of results using 14C content and SOA organic tracer methods. Env. Sci. Technol. 41, 3972-3976.

• Kleindienst et al., 2007, Estimates of the contribution of biogenic and anthropogenic hydrocarbons to secondary organic aerosol at a Southeastern U.S. Location, Atmos. Environ. (in press).

Disclaimer

Although this work was reviewed by U.S. EPA and approved for publication, it may not necessarily reflect official Agency policy.