Secondary Aerosol Formation from Atmospheric Gas and Particle Phase Reactions of Toluene Department of Environmental Science and Engineering, UNC, Chapel Hill Di Hu and Richard Kamens Funded by the USEPA STAR program: July 30, 2003 to July 29, 2006 Dr. Darrell Winner project monitor

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

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

Toluene, m- & p-xylenes, benzene and 1,2,4-trimethyl benzene, o-xylene and ethylbenzene make up 60-75% of this load. In the US, transportation sources contributed ~67% to the total aromatic emissions which are in the range of 2x 10 6 tons/year.

 hydroxy unsaturated dicarbonyls  OH keto-carboxylic acids  Nitrated hydroxy carbonyls Laboratory studies show that gas phase reactions of secondary organic aerosol Laboratory studies show that gas phase reactions of aromatics form a host of oxygenates    secondary organic aerosol material (SOA)

%yield benzaldehyde 8 creosols18 glyoxal12 methylglyoxal12 benzoquinone 6 nitro-toluenes 2 Major products (Calvert et al., 2002)

Edney and Keindienst et al, 2001

Historically “lumped” aromatic kinetic models have focused on Ozone formation: look at the CB4 mechanism ( Gery 1989, Jeffries 2002 ) look at the CB4 mechanism ( Gery 1989, Jeffries 2002 )

{ TOLUENE CHEMISTRY… CB4 } OH + TOL = 0.08 XO CRES HO TO2 TO2 + NO = 0.90*NO *HO *OPEN TO2 = CRES + HO2 OH + CRES = 0.4 CRO XO HO OPEN OPEN = C2O3 + HO2 + CO, OPEN + O3 = 0.03*RCHO C2O HCHO XO CO OH HO MGLY CO OH HO MGLY

CB4 fit to 0.6 ppmC Toluene and 0.4 ppm NOx UNC outdoor aerosol chamber NO NO 2 O3O3

1ppm Toluene ppm NO x NO NO 2 O 3

New aromatic SOA mechanisms: Craig Stroud, Paul Makar et al. (ES&T 2004) used the master mechanism (~300 gas phase reactions) to simulate Toluene and high NOx conc  SOA  organic nitrates dominate the particle phase Griffin et al. and Pun et al. (JGR 2002) modern aromatic mechanism; do not include particle phase reactions; have used it to simulate SOA trends on an airshed scale

A simple reaction scheme for Toluene

. NO 2 +O 2 * O2O2 + CH 3 OH.CH 2 CH 3 H OH H. toluene O=CH CH 3 OH + HO 2 + H 2 O CH 3 O o-cresol benzaldehyde OH H O. H H O H H O H +O 2 CH 3 H + methylglyoxal, glyoxal butenedial pentenedial + HO 2 ring cleavage radical rearrangement CH 3 H OH H CH 3 O O. 3 H OH H. O NO 2 +O 2 oxygen bridge C7 diene-dial

Reaction of 1 st Generation pentene dicarbonyls

TOPEN

Maleic anhydride C5OHALD RALDNO3

ROHACID C4KETALD Tracers

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 reactions + CB4 (2002) chemistry

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

When high concentrations of toluene are added to background chamber air in sunlight, after about 10 minutes particles in the 7-12 nm range appear. When high concentrations of toluene are added to background chamber air in sunlight, after about 10 minutes particles in the 7-12 nm range appear. O 3 = 12 ppb NO = 4-5 ppb NO2= 1-2 ppb fine particles ~1 - 2 ug/m3 ( nm) C2-C10 < 50 ppbC Chamber Post “Nucleation” Observations

Post nucleation (SMPS data) bkg 6 min 10 min 3 min

6 min 10 min 54 min 2.1 hr

There is a need to represent this initial “post nucleation” process… Klotz et al, show experimental evidence that hexadienedials rapidly produce particles when they photolyze. CH 3 OH CH 3 H OH H. * toluene O2O2 + CH 3 H OH H. H NO 2 +O 2 oxygen bridge CH 3 O O methyhexadienedial

Paul Ziemann has proposed that acyl-peroxy radicals can dimerize. CH 3 O O +OH or h  R(=O)OO. acyl-peroxy radical 2 acylperoxy  R(=O)OO(O=)R (SEED) The initial increase in particle number was used as an indicator of the rate of reaction of methlyhexadienedial and pentendial to form seed nuclei

Gas and particle phases were then linked via G/P partitioning i C gas + surf   i C part Gas phase reactions Methyl glyoxal CH 3 -C-C=O particle CH 3 -C-C=O

K p = k on /k off [ i gas] + [part] [ i part] [ i gas] + [part] [ i part] k on k off particle k on k off CH 3 -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 [BENZA gas]+ [C5KETALDp]  [BENZA p]+ [C5KETALDp] kon [BENZAgas]+ [TSP]  [BENZALD p]+ [TSP] kon

Glyoxal in the gas and particle phase CH 3 H methylglyoxal H H glyoxal Vapor pressures ~ 10 torr

Glyoxal in the gas and particle phase (PFBHA)

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 Reactions GLY ----> 500*kon_glyT

heat DMA 2 Smog chamber DMA 1 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 hours 30% 40% 50% 60% Vol. remaining 100 o C

Simulations solid lines: data dashed lines:model dashed lines:model

0.15 ppm Toluene +0.42ppm Propylene in sunlight NO NO 2 O3O3

1ppm Toluene ppm NO x NO NO 2 O3O3

Model simulation of TSP Data model

TSP and SMPS particle mass Filter data SMPS

0.6ppm Toluene ppm NO x NO NO 2 O3O3

Fit to Toluene data data model

Model simulation of TSP Data model

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

What is next ? Experiments over a varity of temperature, light humidity conditions and lower concentrations Particle phase reactions types and rates of oligomer formation “Post Nucleation” rates Quantum yields and photolyis rates of product carbonyls Expansion of the mechanism to other aromatics