John Jayne, Dagmar Trimborn, Hacene Boudries, Jesse Kroll, Doug Worsnop

Center for Aerosol and Cloud ChemistryAerodyne Research, Inc, Billerica, MA

Dahai Tang, Rensheng Deng, Ken SmithDepartment of Chemical Engineering

Massachusetts Institute of Technology

Particle Sampler for On-Line Chemical and Physical Characterization of

Particulate Organics

Atmospheric Science Progress Review MeetingResearch Triangle Park, NC

June 21, 2007

Organic Aerosols• Sources

- POA, Primary organic aerosol, vehicles, factories, biomass burning, etc.

- SOA, Secondary organic aerosol, photochemistry, gas phase precursors.

• Can impact- Health effects- Air quality/visibility- Climate change

How much do we know about the organic fraction of ambient aerosol?

• Can be a significant fraction of total aerosol mass.

• Complex mixture of many individual compounds.

• Advances in understanding depend on faster real-time characterization methods.

• There is a trade off between ability to chemical speciate and measure the total aerosol mass.

Filter Based Methods Organic Aerosol Composition

• GC-MS of extracted organics.

• Identify hundreds of individual molecules, useful as tracers for primary emissions.

• Only 10% or so of total organic mass characterized.

• Long sampling times, 6-24 hrs.

Speciation results for organic aerosol in Southern California (Rogge et al., 1993).

High post collection analysis costs

Org SO42- NO3

- NH4+ Zhang et al, GRL 2007

Aerosol Mass Spectrometer Measurements A bulk measurement - limited speciation

Fast time resolution allows correlations with gas phase species…insight into chemical processing.

Aerosol Collector Module Concept

• Builds on aerosol lens technology used in the AMS

- particle concentrator- minimize gas phase collection

• Size segregated sampling – aerodynamic sizing based on particle velocimetry.

• Can couple to existing gas phase detectors– GC/MS, GC-GC/MS, PTRMS

Aerosol Collector ModuleSchematic - ACM

Thermally isolating support

Carrier gas

Thermal body

Cartridge heater

(-50 < T,C < 350)

LN2 Cooling

Thermocouple

Automated

Automated

Particle Beam

Organic Vapor to Transfer Line

Vacuum isolation valve

Schematic of Aerosol Collector

Particle collection under high vacuum conditions minimizes gas phase contaminates

CARRIERGAS IN

VENT &BACKFLUSH

PR

4PV

TO GAS ANALYZER

TO VACUUMCHAMBER

PR

4PV

ACM

D) INJECTIO N / TRANFER

CARRIERGAS IN

VENT &BACKFLUSH

PR

4PV

TO GAS ANALYZER

TO VACUUMCHAMBER

PR

4PV

ACM

D) INJECTIO N / TRANFER

CARRIERGAS IN

VENT &BACKFLUSH

PR

4PV

TO GAS ANALYZER

TO VACUUMCHAMBER

PR

4PV

ACM

C) DESO RPTION / FLASH EVAPORATIO N

CARRIERGAS IN

VENT &BACKFLUSH

PR

4PV

TO GAS ANALYZER

TO VACUUMCHAMBER

PR

4PV

ACM

C) DESO RPTION / FLASH EVAPORATIO N

CARRIERGAS IN

VENT &BACKFLUSH

PR

4PV

TO GAS ANALYZER

TO VACUUMCHAMBER

PR

4PV

ACM

B) SAMPLING

CARRIERGAS IN

VENT &BACKFLUSH

PR

4PV

TO GAS ANALYZER

TO VACUUMCHAMBER

PR

4PV

ACM

B) SAMPLING

CARRIERGAS IN

VENT &BACKFLUSH

PR

4PV

TO GAS ANALYZER

TO VACUUMCHAMBER

PR

4PV

ACM

A) STANDBY / BACKFLUSH

CARRIERGAS IN

VENT &BACKFLUSH

PR

4PV

TO GAS ANALYZER

TO VACUUMCHAMBER

PR

4PV

ACM

A) STANDBY / BACKFLUSH

Inject

Load Inject

Load

Inject

Load

InjectLoad

1

2

1

2

1

2

1

2

Back-flush Sampling

Desorption Transfer

Volatilized Aerosol Sample Transfer System

Two 4-port Valco valves, 350C max temperature

Prototype ACMConnected to a GC/MS detector

ACM

GC/MS

see poster presented by Dahai Tang.

Agilent6890 GC5973 MS

StandbyCollection (>-50C)

Desorption

Back-flush (<350C)

Time (~ 1hr)

Tem

pera

ture

(-20

to 3

50C

)Program Cycle

Automated cycle controlled by microcomputer

2

4

68105

2

4

68106

2

4

68

Tota

l Ion

Inte

nsity

(arb

.)

24222018161412

Elution Time, min

Total Ion Current

4000

3000

2000

1000

0

Ion

Inte

nsity

(arb

.)

25020015010050

AMU

Decane

100x103

80

60

40

20

0

Ion

Inte

nsity

25020015010050

AMU

Tetradecane

ACM data from a hydrocarbon standard

Dec

ane

unde

cane

Dod

ecan

e

tetra

deca

ne

Hex

adec

ane

Oct

adec

ane

C10 to C18

ACM Paraffin Candle Soot Sample

200x103

150

100

50

0

TIC

201816141210

Time (min)

Peak assignments from NIST Mass Spectral Library

Hex

adec

aneN

apth

alen

e

Trid

ecan

e

Tetra

deca

ne

Pen

tade

cane

6x106

5

4

3

2

1

0

TIC

18.017.517.016.516.015.515.0

Time (min)

6103

2

46

104

2

46

105

2

4

Abun

danc

e

30025020015010050

AMU

Octadecane (m/z 254)

mss_1286

Octadecane GC/MS Sample

C18H38

30x106

25

20

15

10

5

0

TIC

Are

a

76543210

Octadecane mass (ug)

Detection Linearity

Blank/memory effectGlass coated transfer line and coatings on collector help

reduce memory effects, but not eliminated.

Aerosol loadings generated using DMA and CPC.

Effect of collector coating20x103

15

10

5

0

ion

sign

al (H

z): u

ncoa

ted

colle

ctor

806040200temperature (C)

10000

8000

6000

4000

2000

0

ion signal (Hz): Kiss-cote

m/z 100: uncoated m/z 100: Kiss-cote

adipic acid

Coating reduces “tailing”

4000

3000

2000

1000

sign

al/a

rb. u

nit

140012001000800

time/s

Valve and Transfer line Temperature 150 C 200 C

Effect of Temperature on Transfer of Volatilized SampleProton Transfer Reaction Mass Spectrometer (PTRMS)

Motor Oil Sample

Higher transfer line and valve temperatures improve transfer times…coatings are important.

High temperatures can degrade oxidized aerosol

14x103

12108642

Sig

nal (

a.u.

)

1208040AMU

mss_run19mz44 (CO2)45x103

40

35

30

25

20

GC

MS

TIC

(Hz)

6.56.05.55.04.54.03.5

Time (min)

3/27/06 Oleic acid polydisperse. GC oven fixed at 200C100C desorption, 200C xfer line, 150C Valco6 min desorption time

3x106

2

1

0GC

Res

pons

e (T

IC, H

z)

8006004002000

Sampled Mass (ug)

• Molecular identification is compromised.• Response is still linear…

Oleic AcidC18H34O2MW 282.47

TAG: semi-continuous GC-MS of impacted aerosol

Brent Williams, Allen Goldstein, Susanne Hering

Only 30-40% of total organic is eluted

Chebogue Point, Nova Scotia, 2004

Direct Vacuum Desorption Aerosol Collection and volatilization directly inside ionizer of mass spectrometer.

• No transfer line issues, minimize thermal degradation.

• No sample dilution, desorb directly into ionization volume.

• Similar to PBTDMS by Ziemann

Direct Vacuum Desorption System

Collaboration with Paul Ziemann, UC Riverside

and Tofwerks, Switzerland

cartridgeheater

coldfinger

ionizationregion

collector/desorber

High Resolution Mass SpectrometrySoft ionization schemes

Particle beam

Factor analysis for component classification

20x103

15

10

5

0

m/z

264

coun

ts(H

z)

806040200temperature (C)

200x103

150

100

50

0

m/z

185counts

(Hz)

m/z 264: oleicm/z 185: DEHS (b) mixture

Temperature-programmed desorption (TPD):Separation of organics by volatility

0.10

0.08

0.06

0.04

0.02

0.00

200180160140120100806040m/z

pure oleic acid PMF component 1

5

4

3

2

1

0

Nitr

ate

Equi

vale

nt M

ass

Con

cent

ratio

n (µ

g m

-

200180160140120100806040m/z

60

40

20

0

x10-3

pure DEHS PMF component 2

Factor analysis for component classification

• Positive Matrix Factorization - PMF to deconvolvespectra into components.

•Can also be applied to GC/MS spectra.

30025020015010050m/z (amu)

282

264

55

264

(M-H20)

288

281

(Li-M+)

59CH3COO-

41

25

41

43

45HCOO-

C2H-

Oleic acid (282 m/z)Electron impact Photoionization Li+ attachment Negative Ions

Comparison of mass spectra of oleic acid obtained with four different ionization methods.

Soft ionization schemes for improved molecular identification.

Summary• An Aerosol Collector Module was built and

evaluated using a GC/MS and a PTRMS. – Coatings and transfer lines control throughput and

molecular identification, thermal degradation.– Current detection levels are useful for lab studies.– Evaluation is ongoing.

• Direct vacuum desorption – Avoids valves and transfer lines.– No sample dilution.– High resolution spectrometry and soft ionization

schemes.

Future Direction• Plan to do more with ACM-GC/MS

– Collaboration with Glenn Fyrsinger, USCG, 2D-GC/MS.

• Further explore vacuum desorption– Minimize transfer line losses and thermal degradation.– Higher time resolution.– Higher sensitivity, no sample dilution by carrier gas.

• takes full advantage of particle concentration, i.e. air removal– Utilize high-resolution mass spectrometric methods and alternate

soft ionization schemes for molecular ID.• e.g. PTRMS, chemical ionization.

• Integrate particle velocity selector for size resolved measurements.

• PM2.5 aerodynamic lens development.– See poster by Dahai Tang.

AcknowlegdementsEPA STAR programDoE SBIR program

Paul Ziemann, Allen Goldstein, Susanne Hering, Tofwerks