Secondary Aerosol Formation from Secondary Aerosol Formation from Gas and Particle Phase Reactions Gas and Particle Phase Reactions

of Aromatic Hydrocarbons of Aromatic Hydrocarbons

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, 2006

The objective of this projectThe objective of this project is to is to develop a simple “efficient” multi-phase develop a simple “efficient” multi-phase chemical mechanism that will predict chemical mechanism that will predict secondary organic aerosol formation from secondary organic aerosol formation from aromatic atmospheric reactionsaromatic atmospheric reactions

Volatile aromaticVolatile aromatic compounds compounds comprise a significant part of the comprise a significant part of the urban hydrocarbon mixture in the urban hydrocarbon mixture in the atmosphere, up to 45% in urban atmosphere, up to 45% in urban

US and European locationsUS and European 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 range from 2.4 x 10emissions which range from 2.4 x 1066 to 1.9 x 10to 1.9 x 1066 tons/year tons/year. .

hydroxy unsaturated dicarbonyls

di and tri 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)

Edney and Keindienst et al, 2001

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

illustrate how these fit smog chamber illustrate how these fit smog chamber data; solid lines = data, dashed lines = data; solid lines = data, dashed lines = model)model)

look at a mechanismlook at a mechanism

CB4 fit to 4 ppmC TolueneCB4 fit to 4 ppmC Tolueneand 0.4 ppm NOxand 0.4 ppm NOx

UNC outdoor aerosol chamberUNC outdoor aerosol chamber

{ 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

Jang and Kamens, 2001

CH3

OH OHCH2.

NO NO2

+O2

CH3

H

OH

H .

*

O2

+ toluene

O=CHCH3

OH

+ HO2

+ H2O

CH3

O

o-cresolbenzaldehyde

CH3

H

OH

H

CH3

O

O

.CH3

H

OH

H

.O

NO

NO2

+O2

rearrangement

oxygen bridge

OH

H

O .

H

H

O

H

OH

H

O

H

+O2

CH3H+

methylglyoxalbutenedial

+ HO2

ring cleavageradical

Pent-dione + OHPent-dione + OH 0.5 0.5 pent-rad +0.5 pent-oopent-rad +0.5 pent-oo    pent-oo pent-oo XOXO

22 + 0.5 GLY+ 0.5 MGLY + 0.5 GLY+ 0.5 MGLY

+ 0.5 CO + 0.5HO2 +0.25 OHoxybutal+ 0.5 CO + 0.5HO2 +0.25 OHoxybutal +0.25 but-tricarb +0.25 but-tricarb

pent-rad pent-rad Maleic + 1.5 XO Maleic + 1.5 XO22 + HO + HO

22 + HCHO + HCHO

 

New Mechanism has 44 reactions New Mechanism has 44 reactions  

hexadiene-dicarb hexadiene-dicarb butene-dicarbonylbutene-dicarbonylpentene-dicarbonylpentene-dicarbonylbenzaldehydebenzaldehydecresolcresolmaleic anhydridemaleic anhydride

43 AROMATIC reactions43 AROMATIC reactions + Carbon 4 + Carbon 4

Chamber Post “Nucleation” ObservationsChamber Post “Nucleation” Observations

When high concentrations of toluene are When high concentrations of toluene are added to background air chamber in sunlight, added to background air chamber in sunlight, after about 10 minutes particles in the 7-12 after about 10 minutes particles in the 7-12 nm range appear.nm range appear.

 

OO33 = 12 ppb = 12 ppb

NO = 5-6 ppbNO = 5-6 ppb

NO2= 1-2 ppbNO2= 1-2 ppb

fine particles ~4-5 ug/m3 (70-120 nm) fine particles ~4-5 ug/m3 (70-120 nm)

C2-C10 < 50 pppCC2-C10 < 50 pppC

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

0

50000

100000

150000

200000

250000

300000

350000

400000

1 10 100 1000Dp (nm)

dN

/dlo

gD

p (

#/c

m3

)

BKG10:4710:5110:5411:0111:0811:3811:5712:3012:56BKG10:4710:5110:5411:0111:0811:3811:5712:3012:56

There is a need to represent this initial There is a need to represent this initial “post nucleation” process…“post nucleation” process…

Klotz et al, show experimental evidence Klotz et al, show experimental evidence that hexadienedials produce particles that hexadienedials produce particles when they photolyze.when they photolyze.  

CH3

OHCH3

H

OH

H .

*

tolueneO2

+

CH3

H

OH

H

.

HNO

NO2

+O2

oxygen bridge

CH 3O

O

Gas and particle phases can be linked via G/P partitioning

Methyl glyoxal

particle

Gas phase reactions

TSPC

CK

gasi

parti

p

1Cgas + surf 1Cpart

CH3-C-C=O

CH3-C-C=O

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

K

R T

p MwpiL

7 6 0

1 0 6

fom*

Kp = kon/koff

kon

koff

particle

kon

koff

CH3-C-C=O O

TSP = n[BENZAp] +n[C4OHALDp] + n[C5OHALDp] + n[Poly3] + n[Poly1] + n[Poly2] + n[Poly4] + n[Poly5] + n[C4KETALDP] + n[C5KETALDP] + n[OPENP] + n[seed] + n[seed2] + n[RgNO3P] + n[RALDNO3p] + n[RALDACIDp] + n[GLYp] + n[MGLYP] + n[Poly6] + n[Poly7] + n[Poly8] + n[BZONO3P];

[BENZA gas]+ [BENZAp] [BENZA p]+ [BENZAp] kon [BENZA gas]+ [seed] [BENZA p]+ [seed] kon

………

Optimized GAS-Particle Phase kinetics Optimized GAS-Particle Phase kinetics  

[BENZA gas]+ [C5KETALDp] [BENZA p]+ [C5KETALDp] kon

[BENZAp] [BENZA gas] koff

[BENZAgas]+ [TSP] [BENZALD p]+ [TSP] kon

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

CH3

H

methylglyoxal

HH

glyoxal

Vapor pressures ~ 10 torr

TSPC

CK

gasi

parti

p

PFBHAPFBHA O-(2,3,4,5,6-pentafluorobenzyl) O-(2,3,4,5,6-pentafluorobenzyl) -hydroxylamine for carbonyl groups-hydroxylamine for carbonyl groups

FF

F

F F

CH2 O NH2

H2O

PFBHA

R1

C

O

R2

CH2

F F

F

FF

ONC

R1

R2

acetone or ketoneCarbonyl Carbonyl group

PFBHAPFBHA

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

Particle Phase ReactionsParticle Phase Reactions

GLY ----> GLYP @ 500*kon_glyT

GlyP GlyP Poly1 Poly1 kk11

Poly1 ----> GlyPPoly1 ----> GlyP kk-1-1

Gly4OHP + GlyAcidP ----> pre-Poly1Gly4OHP + GlyAcidP ----> pre-Poly1

Pre-Poly1 + C4OHALD ----> Poly1Pre-Poly1 + C4OHALD ----> Poly1

R[TOLP_11a] = GLYP ----> Poly1 @ 500*kpart_T;

R[TOLP_11b] = Poly1 ----> GLYP @ kpart_off;

GLYgas + part GLYpart + part

500*kon

Toluene + PropyleneToluene + Propylene

Simulation of 4 ppmC Toluene + Simulation of 4 ppmC Toluene +

0.4 ppm NO0.4 ppm NOx x experiment in sunlightexperiment in sunlight

NONO2

O3

Fit to Toluene dataFit to Toluene data

data

model

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

Model simulation of TSPModel simulation of TSP

Datamodel

Model Simulation of Toluene/NOModel Simulation of Toluene/NOxx Experiment on 11/15/04Experiment on 11/15/04

Hours EST

pp

mV

Toluene Products

Hours EST

pp

mV

Toluene Products

carbonyl-PANcarbonyl-PAN

C4-carbonyl-acid C4-carbonyl-acid

butane-tricarbonyl butane-tricarbonyl

OH-oxobutanal OH-oxobutanal

polymer1 polymer1

A second generation ModelA second generation Model

A second generation ModelA second generation Model

PFBBr,PFBBr, Pentafluorobenzyl bromidePentafluorobenzyl bromide derivatization for carboxylic and aromatic-OHderivatization for carboxylic and aromatic-OH

CH2 C

O

OH

H3C CH3

C

O

H O

FF

F

F F

CH2Br

C CH2

O

HO C O CH2

F F

F

FF

OH3C CH3

HBr

PFBBr

C CH2

O

O C O CH2

F F

F

FF

OCH3 CH3

CH2

FF

F

F F

2 HBr

AnalysisAnalysis

BSTFABSTFA for hydroxyl, and/or carboxylic groupsfor hydroxyl, and/or carboxylic groups

BSTFA

R OH

carboxylic acid or alcohol

C N

Si(CH3)3

CF3

O(CH3)3Si

R

O(CH3)3Si

BFBF33-CH-CH33OH + BSTFA OH + BSTFA Derivatization MethodDerivatization Method

C

O

HO CH2 C

OH

C

CH3

O

OH + CH3 OHBF3

excess

C

O

CH3O CH2 C

OH

C

CH3

O

OCH3

C

O

CH3O CH2 C

O

C

CH3

O

OCH3

Si(CH3)3

C NSi(CH3)3F3C

O

Si(CH3)3

C

O

CH3O CH2 C

OH

C

CH3

O

OCH3 +

excess

+

C NHSi(CH3)3F3C

O

C NH2F3C

O

TMCS

GC-ITMS analysisGC-ITMS analysis

- electron impact ionization (EI)- electron impact ionization (EI)

- methane chemical ionization (CI-methane)- methane chemical ionization (CI-methane)

- tandem mass spectrometry (MS/MS)- tandem mass spectrometry (MS/MS)

Citramalic acid

What are some challengesWhat are some challenges??

Photolysis reactions of the 2Photolysis reactions of the 2ndnd and 3 and 3rdrd productsproducts

Quantum yields of product carbonylsQuantum yields of product carbonyls

Particle phase reactionsParticle phase reactions

Wall reactions of the productsWall reactions of the products