Secondary Aerosol Formation from Secondary Aerosol Formation from Atmospheric Gas and Particle Atmospheric Gas and Particle Phase Reactions of ToluenePhase Reactions of Toluene

Department of Environmental Science and Engineering, UNC, Chapel Hill

Di Hu and Richard KamensFunded by the USEPA STAR Funded by the USEPA STAR program: July 30, 2003 to program: July 30, 2003 to July 29, 2006July 29, 2006Dr. Darrell Winner project Dr. Darrell Winner project monitormonitor

A simpleA simple “efficient” multi-phase “efficient” multi-phase chemical mechanism for chemical mechanism for predicting secondary organic predicting secondary organic aerosol formation from toluene aerosol formation from toluene atmospheric reactionsatmospheric reactions

Volatile aromaticVolatile aromatic compounds compounds comprise up to 45% of the comprise up to 45% of the atmospheric volatile hydrocarbon atmospheric volatile hydrocarbon mixture, in urban US and mixture, in urban US and

European locationsEuropean locations

Toluene, m- & p-xylenes,Toluene, m- & p-xylenes, benzene and benzene and 1,2,4-trimethyl benzene, o-xylene and 1,2,4-trimethyl benzene, o-xylene and ethylbenzene make up 60-75% of this ethylbenzene make up 60-75% of this load. load.

In the US, transportationIn the US, transportation sources sources contributed ~67% to the total aromatic contributed ~67% to the total aromatic emissions which are in the range of emissions which are in the range of 2x 102x 1066 tons/year tons/year. .

hydroxy unsaturated dicarbonyls

OH keto-carboxylic acids

Nitrated hydroxy carbonyls

Laboratory studies show that gas phase Laboratory studies show that gas phase reactions ofreactions of aromatics form a host of oxygenates secondary organic secondary organic aerosolaerosol material (SOA)

%yield%yieldbenzaldehydebenzaldehyde 8 8creosolscreosols 1818glyoxalglyoxal 1212methylglyoxalmethylglyoxal 1212benzoquinonebenzoquinone 6 6nitro-toluenesnitro-toluenes 2 2

Major products (Calvert et al., 2002)

Edney and Keindienst et al, 2001

HistoricallyHistorically “lumped” “lumped” aromaticaromatic kinetic kinetic models have focused on Ozone models have focused on Ozone formation:formation:

look at the CB4 mechanism (look at the CB4 mechanism (Gery 1989, Gery 1989,

Jeffries 2002Jeffries 2002))

{ TOLUENE CHEMISTRY… CB4 }{ TOLUENE CHEMISTRY… CB4 }

OH + TOL = 0.08 XO2 + 0.36 OH + TOL = 0.08 XO2 + 0.36 CRESCRES + 0.44 HO2 + 0.56TO2 + 0.44 HO2 + 0.56TO2

TO2 + NO = 0.90*NO2 + 0.90*HO2 + 0.90*OPENTO2 + NO = 0.90*NO2 + 0.90*HO2 + 0.90*OPEN

TO2 = TO2 = CRESCRES + HO2 + HO2

OH + OH + CRESCRES = 0.4 CRO + 0.60 XO2 + 0.60 HO2 + 0.30 OPEN = 0.4 CRO + 0.60 XO2 + 0.60 HO2 + 0.30 OPEN

OPEN = C2O3 + HO2 + CO,OPEN = C2O3 + HO2 + CO,

OPEN + O3 = 0.03*RCHO + 0.62 C2O3 + 0.70 OPEN + O3 = 0.03*RCHO + 0.62 C2O3 + 0.70 HCHOHCHO + 0.03 XO2+ 0.03 XO2

+ 0.69 CO + 0.08 OH + 0.76 HO2 + 0.2+ 0.69 CO + 0.08 OH + 0.76 HO2 + 0.2 MGLYMGLY

New aromatic SOA mechanisms:New aromatic SOA mechanisms:

Craig Stroud, Paul MakarCraig Stroud, Paul Makar et al. ( et al. (ES&TES&T 2004) used the master mechanism (~300 gas 2004) used the master mechanism (~300 gas phase reactions) to simulate Toluene and phase reactions) to simulate Toluene and high NOx conchigh NOx conc SOA SOA organic nitrates organic nitrates dominate the particle phasedominate the particle phase

Griffin et al. and Pun et al. Griffin et al. and Pun et al. ((JGRJGR 2002) 2002) modern aromatic mechanism; do not include modern aromatic mechanism; do not include particle phase reactions; have used it to particle phase reactions; have used it to simulate SOA trends on an airshed scalesimulate SOA trends on an airshed scale  

A simple reaction scheme for TolueneA simple reaction scheme for Toluene  

.

NO NO2

+O2

*

O2

+

CH3

OH OH

.CH2 CH3

H

OH

H .toluene

O=CHCH3

OH

+ HO2

+ H2O

CH3

O

o-cresolbenzaldehyde

OH

H

O .

H

H

O

H

OH

H

O

H

+O2

CH3H+

methylglyoxal,glyoxal

butenedialpentenedial

+ HO2

ring cleavageradical

rearrangement

CH3

H

OH

H

CH3

O

O

.CH3

H

OH

H

.O

NO

NO2

+O2

oxygen bridgeC7 diene-dial

Reaction of 1Reaction of 1stst Generation Generation pentene dicarbonylspentene dicarbonyls

TOPENTOPEN

Maleic anhydride

C5OHALD

RALDNO3

ROHACID

C4KETALD

Tracers

New Mechanism has:New Mechanism has:

50 gas phase reactions 50 gas phase reactions 24 gas to particle phase “reactions”24 gas to particle phase “reactions”16 particle phase reactions16 particle phase reactions+ CB4 (2002) chemistry+ CB4 (2002) chemistry

 

After an initial nucleation, we are assuming After an initial nucleation, we are assuming that gas particle partitioning of products that gas particle partitioning of products dominates the formation of new particle dominates the formation of new particle mass. mass.

 

Post nucleation (SMPS Post nucleation (SMPS data)data)

bkg

6 min

10 min

3 min

Gas and particle phases were then linked via G/P partitioning

TSPC

CK

gasi

parti

p

iCgas + surf iCpart

Gas phase reactions

Methyl glyoxal

CH3-C-C=O

particle

CH3-C-C=O

K

R T

p MwpiL

7 6 0

1 0 6

fom*

Kp = kon/koff

[ [ iigasgas] + [part] ] + [part] [ [ iipartpart]] kon

koff

particle

kon

koff

CH3-C-C=O O

Glyoxal in the gas and Glyoxal in the gas and particle phaseparticle phase

CH3

H

methylglyoxal

HH

glyoxal

Vapor pressures ~ 10 torr

TSPC

CK

gasi

parti

p KR T

p MwpiL

7 6 0

1 0 6

fom*

Glyoxal in the gas and Glyoxal in the gas and particle phase (PFBHA)particle phase (PFBHA)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

10:27 11:32 12:34 13:40 14:38 15:32

Time

part

gas

GLYgas + TSP GLYpart 500 x kon

Kalberer et al. (Science, 2004) show that oligomerization occurs at a rapid rate in aerosol from 1,3,5 TriMe benzene + NOx + light

MGLY and GLY and other carbonyls may participate in this particle phase reaction

Particle phase reactions

Particle Phase ReactionsParticle Phase Reactions

GLY ----> GLYP @ 500*kon_glyT

heat

DMA2

Smog chamber

DMA1

Volatile Tandem DMA system

Based on the tandem DMA experiments, which are interpreted to show oligomer formation over time, we calculated rates of formation

Plot volume fraction remaining vs. reaction time in the chamber

1 2 3 4 5 6hours

30%

40%

50%

60%V

ol.

re

mai

nin

g

100oC

SimulationsSimulations

solid lines:solid lines: data data

dashed lines:dashed lines: model model  

0.15 ppm Toluene +0.42ppm 0.15 ppm Toluene +0.42ppm Propylene Propylene in sunlightin sunlight

NONO2

O3

1ppm Toluene + 0.33 ppm NO1ppm Toluene + 0.33 ppm NOxx

NONO2

O3

Model simulation of TSPModel simulation of TSP

Datamodel

TSP and SMPS particle massTSP and SMPS particle mass

0

50

100

150

200

250

300

11:31 13:55 16:19 18:43 21:07

Time (EDT)

Parti

cle

Mass (

ug

/m3)

Filter data

SMPS

0.6ppm Toluene + 0.4 ppm NO0.6ppm Toluene + 0.4 ppm NOx x

NONO2

O3

Fit to Toluene dataFit to Toluene data

data

model

Model simulation of TSPModel simulation of TSP

Data

model

%

Components of the particle phaseComponents of the particle phase(very, very tentative)(very, very tentative)

oligomers 30post nucleation 10ring NO3 3alkyl NO3 2OHC4ketoaldehydes 30OH C4Ketoacids 25

What is nextWhat is next??Experiments over a varity of temperature, light Experiments over a varity of temperature, light humidity conditions and lower concentrationshumidity conditions and lower concentrations

Particle phase reactionsParticle phase reactionstypes and rates of oligomer formationtypes and rates of oligomer formation

““Post Nucleation” ratesPost Nucleation” rates Quantum yields and photolyis rates of product Quantum yields and photolyis rates of product carbonylscarbonyls

Expansion of the mechanism to other aromaticsExpansion of the mechanism to other aromatics