Envr 890 Organic Aerosols: Lecture 2 Envr 890 Organic Aerosols: Lecture 2. What questions do we have to start asking if we are to build a kinetics model to predict aerosol formation from isoprene reactions? kamens@unc.edu http://www.unc.edu/~kamens

Objective To describe a predictive technique for the formation of aerosols from biogenic hydrocarbons based on fundamental principals and apply it to isoprene Have the ability to embrace a range of different atmospheric chemical and physical conditions which bring about aerosol formation.

Chemical System + NOx+ sunlight + ozone----> aerosols a-pinene

Overview This reaction system produces low vapor pressure reaction products that distribute between gas and particle phases.

Gas Particle Partitioning gas phase products COOH O cis-pinonic acid particle

Equilibrium partitioning between the gas and particle phases is assumed for all products. Kinetically this is represented as forward and backward reactions. Kp = kon/koff

The equilibrium constant Kp can be calculated from [gas] + [surface] [particle]

Overview Gas and particle phase reactions were linked in one mechanism and a chemical kinetics solver was used to simulate the reaction over time Model simulations were compared with aerosol concentrations obtained by reacting -pinene with either O3 or NOx in sunlight in an outdoor chamber.

-pinene-O3 experiments in the UNC 190m3 outdoor chamber 1. added O3 O3 -pine O3 2. added -pinene O3 O3 -pine O3 O3 -pine

-pinene-O3 experiments in the UNC 190m3 outdoor chamber 1. added O3 O3 -pine O3 2. added -pinene O3 O3 -pine 3. immediate burst of particles O3 O3 -pine

Products pinald - pinacid - diacid - oxy-pinald - oxy-acid- pinonaldehyde CHO O nor-pinonaldehyde Pinic acid HOOC COOH COO C8 diacid OH Pinonic acid Norpinonic acid

Mechanism OH Criegee2 Criegee1 + other products + CO, HO a -pinene pinonic acid CHO COOH + CO, HO 2, OH norpinonaldehyde norpinonic acid Mechanism CHO O CH 3 Criegee2 Criegee1 O a -pinene 3 COOH pinic acid + other products

Now you need to know about the reactions of alkenes with O3 C=C +O3 See pages Pitts and Pitts, 2000, pages 179-206

How do we chemically represent his reaction scheme? 1st the reaction of O3 with an alkene generates an aldehyde +a high energy bi-radical called a Criegee bi-radical 2nd a certain fraction of these “hot” Criegee’s stabilize and the rest decomposes. (see page 198 of Pitts and Pitts, Table 6.10) 3rd “Hot” Criegee’s R-(H)C.-00. decompose to OH, CO and an R. group

For the propylene +O3 reaction (page 198 Pitts and Pitts) propylene +O3  two Criegee’s C-C=C +O3  H2C.OO.* + CH3C.HOO.* + what two aldehydes? CH3C.HOO.* 0.15 Stabilized Criegee  0.54 (CH3. + CO +OH.)  CH3. + CO2+ H.  HCO +CH3O 0.17  0.14 (CH4 + CO2)

How do we chemically represent this for the a-pinene system? apine + O3  0.4*crieg1 + 0.6*crieg2 min-1 or ppm-1min-1 1.492 e-732/T More highly substituted Criegee’s are more stable crieg1 = 0.47*pinacid + 0.13*stabcrieg1 1x106 + 0.8*OH + 0.3*HO2 + 0.37*pinald + 0.01*oxypinald + 0.03*O. + 0.19*CO

What would we do for isoprene (see Kamens et al, IJKS, 1982?

OH attack on a-pinene CHO O OH HOO + OH 2 OO a-pinene pinonaldehyde

Each Reaction can be represented as a differential equation a-pinene + ozone --> pinald d[a-pinene]/dt = -krate1 [a-pinene][O3] d[pinald]/dt = -krate2[pinal][OH]

Particle formation-self nucleation

Particle formation-self nucleation Criegee’s can react with aldehydes and carboxylic groups to form secondary ozonides and anhydrides. O=C C=O CH 3 + C . oo. C C=O CH 3 O oo

Estimating rates that gas phase products enter and leave the particle The equilibrium between the gas and particle phases is: Kp = kon/koff

Kp = kon/koff The equilibrium constant Kp can be calculated from [gas] + [surface] [particle] Kp = kon/koff

A general Flux expression for evaporation from a liquid surface is  is the energy barrier for single molecule to evaporate from the surface (Joules) koff = k evap  in koff =  e -Ea/RT is: kbT/h From koff and Kp the rate coefficient kon can now be calculated

Overall Mechanism linked gas and particle phase rate expressions

Where do the rate coefficients come from?? Diacid is generated in the gas phase. How do we get it on and off the particle phase?? diacidgas + pinacidpart --> pinacidpart + diacidpart 68 diacidpart  diacidgas 3.73x1014 e-10285/T Where do the rate coefficients come from??

Kp = kon/koff koff =  e -Ea/RT We need vapor pressure (poL ) to calculate Kp for koff , we need kbT/h for , and an activation energy, Ea To calculate vapor pressures see Chapter 4 of (Schwarzenbach et al, Environmental Organic Chemistry, 2003)

if we substitute DSvap Tb= 88J mol-1 K-1 and R =8.31 Jmol-1 K-1 This means we need Tb or boiling point

Boiling points can be estimated based on chemical structure (Joback, 1984) Tb= 198 + S DTb   DT (oK) -CH3 = 23.58 K -Cl = 38.13 -NH2 = 73.23 C=O = 76.75 CbenzH- = 26.73 C-OH = 93   Joback obs (K) (K) acetonitrile 347 355 acetone 322 329 benzene 358 353 amino benzene 435 457 benzoic acid 532 522 toluene 386 384 pentane 314 309 methyl amine 295 267 trichlorethylene 361 360 phenanthrene 598 613  

Stein, S.E., Brown, R.L. Estimating Normal boiling Points from Group Contributions, J.Chem. Inf Comput. Sci, 34, 581-587, 1994

Chamber Data First look at experiments with different temperatures and gas phase concentrations of -pinene and ozone

A high concentration warm experiment 0.82 ppmV -pinene + 0.60 ppm O3 Temp = ~295K %RH = ~61%

Gas Phase -pinene and O3 data and model 

Particle concentration. Warm high concentration experiment Reacted -pinene mg/m3 Observed model

Other Conditons 0.88 ppmv a-pinene + 0.47 ppm O3(269K)

Lower concentration experiments

0.20 ppm a-pinene + 0.11 ppm O3 model data

How do we start to build an Isoprene + O3 mechanism??

The initail attack of O3 on an olefin (alkene) generates two possible Criegee high energy bi-radicals and two possible aldehydes.

A general rule is that the more highly substituted carbon will form a higher fraction of Criegee’s

C=C-C=C + O3  MACR + H2C.OO.  CI1.OO. + HCHO  MVK + H2C.OO.

What would we do for isoprene (see Kamens et al, IJKS, 1982?

There are 4 general product channels by which high energy Criegee’s (Criegee intermediates) decompose: Stabilized Criegee biradicals an Ester Channel O-atom elimination Hydroperoxide channel

The hydroperoxide channel is a source of dark OH Homework 3: For MVK write a set of Chemical equations to show it’s decomposition

MVK + O3 H2C=C - C-CH3 H O (MVK) MVK + O3 MGLY+ H2C.OO.* .OOC.C(H)-C(=O)-CH3 +HCHO let’s assign splitting ratios 2. MVK + O3 0.4 MGLY+ 0.4 H2C.OO.* 0.6 CI2*+0.6 HCHO

MVK + O3 MVK + O3 0.4 MGLY+ 0.4 H2C.OO.* 0.6 CI2 * +0.6 HCHO how does H2C.OO. decompose?? (look at page 197 of Pitts and Pitts,2000) H2C.OO.*  0.37 Stabcrieg1 +0.12 HCO+ 0.12 OH. +0.38 CO+ 0.38 H2O

Stabilized Criegee’s usually react with water Stabcrieg + H2O  Aldehyde +H2O2 H2C.OO.* + H2O H2C=O + H2O2 Stabcrieg + Aldehyde  secondary ozonide How do we add rate constants??

Adding Rate constants MVK + O3 MGLY+ H2C.OO. .OOC.C(H)-C(=O)-CH3 +HCHO 6X10-3 ppm-1 min-1 H2C.00. + H2O H2C=O + H2O2 5.4x10-2 ppm-1 min-1 look in Pitts and Pitts to convert ppm-1 min-1 to cm3molecule-1sec-1

Does OH attack Isoprene, MACR,MVK,MGLY and HCHO??? isoprene + OH  products MACR+ OH  products MVK + OH  products MGLY +OH  products H2C=O +OH  products NO3+alkenes  products radical +radicals  stable products aldehydes photolyze

Light model for a-pinene + NOx a-pinene + OH Noizoire et al. a-pinene + NO3 Martinez et al., Wangberg et al. a-pinene(OH)-OO + NOx--> products Aschmann et al. pinonaldehyde +OH or NO3 Calogirou et al. pinonaldehyde photolysis Hallquist et al acyl peroxy + NO2 --> PAN analogues Noizoire et al. partition nitrate products

pinonaldehyde

Pinonaldehyde chemistry Pinald +hn = 0.65pinO2 + 1.35 CO + HO2 + 0.35*C8O2 ` # hnpinald pinO2 + NO= .765pinald + .85 HO2 + 0.1*acetone +0.2C2O3 + .865NO2 # 6056 exp 180/T C8O2 + NO = NO2 {+ C8-dicarb } # 6056 exp 180/T pinald + OH = . 8 pinald-oo + 0.1C3O2 + 0.1C8O2 + 0.1 acetone +0.3XO2 # 134417, pinald + NO3 = 0.95*pinald-oo +0.03*pinO2 +0.02*C8O2 + 0.07*CO +NO # 79 2 pinald- oo + NO = pinO2 +CO2 +NO # 7915 exp250/T 2 pinald- oo + NO = pinald-PAN #3885exp380/T 2 pinald-PAN = pinald- oo + NO2 # 1.067e11 exp-8864/T pinald- oo + pinald- oo = 2*pinO2 # 2551 pinald- oo + HO2 = Pinacid # 677 @1040

Pinonaldehyde quantum yields in natural sunlight kphototyis = S ( al fl Il ) By adding pinonaldehyde to the chamber in clear sunlight in the presence of an OH scavenger and measuring its rate of decay fl can be fit to the decay data assuming a shape with wave length similar to other aldehydes

Pinonaldehyde quantum yields in sunlight Normalized to one pinonaldehyde CH3CH2CH2=O CH2=O O pinonaldehyde CH3CH2=O

0.97 ppm a-pinene + 0. 48ppm NOx; October Sunlight

a-pinene data vs. model model data

Gas phase pinonaldehye model pinonaldehyde O data norpinonaldehyde

Particle phase pinonic acid model pinonic acid data norpinonic acid

Measured particle mass vs. model Particle phase model mg/m3 S products filter data

0.95 ppm a-pinene + 0. 44ppm NOx model data NO O3 NO2 NO2

Measured particle mass vs. model reacted a-pinene data model

Gas phase pinonaldehye

particle phase pinonaldehye data model

d-limonene + O3 (Sirakarn Leungsakul, ES&T 2004)

Major particle phase products keto-limononaldehyde limononaldehyde 7OH-limononic acid 7OH-limononaldehyde 7OH-keto-limononaldehyde 7OH-keto-limononic acid keto-limononic acid

d-limonene keto-limald limononaldehyde limonalic acid 0.68 + CH -OO 2 0.15 OOO 0.32 + O 3 O keto-limonene 0.85 OO 0.30 O O O + H O 0.35 O 0.50 2 OH 0.63 O OO OO limononic acid 0.65 Stab-Crieg1 Crieg1* 0.37 + H O O 2 O + OH OO O 0.25 OO 0.20 + H O 2 O O O 0.20 O keto-limald + H O Stab-Crieg2 limononaldehyde 2 Crieg2* OH 0.10 HO O CH -OH + 3 O O limonalic acid O 7OH-limononaldehyde

d-limonene + O3 (Sirakarn Leungsakul, 2004) aerosol (mg/m3)v ppmV aerosol (mg/m3)v Filter data and Model O3

d-limonene + O3 (Sirakarn Leungsakul, 2004) Filter Model O3 .00 .02 .04 .06 .08 .10 18 19 20 21 22 23 24 1:00 LDT (hour) (ppm) 0.00 30 60 90 120 150 aerosol (mg/m3) O3 Filter d-limonene + O3 (Sirakarn Leungsakul, 2004) Model

b-pinene + O3 (Mohammed Jaoui, 2003)

b-pinene + O3

* toluene O2 . . OH oxygen bridge rearrangement butenedial O=CH CH 3 OH + HO 2 + H O o-cresol benzaldehyde CH 3 OH 2 . NO +O H * O2 + toluene CH 3 H OH O . NO 2 +O rearrangement oxygen bridge OH H O . +O 2 CH 3 + methylglyoxal butenedial + HO ring cleavage radical

Experiments that explore heterogeneous carbonyl reactions (Myoseon Jang et al., Science, 2002) Nebulizes NH4(SO4)2 acid coated aerosols into Teflon bags Reacts aldehydes on the surface of the acid coated particles (~2% H2SO4 by weight) Diesel exhaust is 1-5% sulfuric acid Aldehyde products such as pinonaldehyde, norpinonaldehyde, hydroxy pinonaldehyde, and oxo-pinonaldehyde are products from the a-pinene/ozone reaction and Methacrolein and formaldehyde are common products of the ozonation of isoprene In addition, the indigenous acid in many aerosol systems would be able to catalyze these reactions BE CLEAR: These heterogeneous reactions take place in the particle phase and use the acid present in the particle phase as a catalyst Thus we wanted to test how an aldehyde would interact on acidic particles compared to non acidic particles and what we found was that when particle phase acids are present, more SOA mass is observed than in a non acid environment

500 liter Teflon bag nebulizer (NH4)2SO4 (NH4)2SO4+H2SO4 Solution aldehydes alcohols glyoxal

The aldehyde phenomenon can be explained as follows: Aldehyde functional groups can further react in the aerosol phase through heterogeneous reactions via hydration, polymerization, and hemiacetal/acetal formation with alcohols. Aldehyde reactions can be radically accelerated by acid catalysts such as particle sulfuric acid

Acid catalyzing step Hydration Polyimerization OH O H + H O OH + -H 2

Hemiacetal and acetal formation OH + OH OH -H H H + ROH R H O H OR H H H hemiacetal + OH + -H O OR OH H 2 2 H H H OR H H H OR + H O OR R ROH -H acetal

Aerosol yields from aldehydes Notice greater yields for all aldehydes when an acid catalyst is present. Now that we had confirmed that some sort of reaction beyond partitioning was taking place and that the reactions were catalyzed by an acid we can consider a few examples of possible heterogeneous reactions that are taking place *Yield data and method from Jang et al. 2001

Acid seed experiments with O3 + organics Nebulizer Ozone Volatilized organics Ozone (NH4)2SO4 Solution (NH4)2SO4+H2SO4 This is basically the same system as was used in the aldehyde experiments. The only real difference is that ozone is present initially so that when the organics are injected, gas phase oxidation reactions happen immediately. The time scale of these experiments was on the order of about an hour (much longer compared to the flow reactor) and differ in that the seed aerosol is present from the very beginning of SOA production, not added at a late time.

Yields from Teflon bag experiments Again in each case the yield is much higher in the acidic systems. This increase is especially evident for a-pinene and isoprene. Thus heterogeneous reactions are a role player in biogenic SOA systems in which a SOA precursor must react to form the aldehydes which participate in the heterogeneous reactions. These increases are much greater than those observed in the flow reactor indicating that heterogeneous reactions become more important at longer time scales. It would be interesting to look at even longer time scales and judge the extent of heterogeneous reactions.

Aldehyde acid catalyzed heterogeneous reactions Acid catalyzing step Hydration Polymerization H O OH H+ O OH H + H 2 The effect is noticed in the presence of an acid catalyst. So the reactions must at least be aided by an acid. I will demonstrate only a few of the possibilities here. We have targeted carbonyls as the primary participating group. So the catalytic step would be protonation of the carbonyl group. From there a variety of reactions could happen. I’ll mention a few: hydration to the gem diol and from there it can undergo polymerization with other carbonyls. Such a reaction chain could lead to long chain polymers Note that the ultimate result of these reactions is to convert the carbonyl group of the aldehyde into hydroxy groups and C-O bonds. H OH O + Etc...

Particle Phase reactions Gas phase reactions C=O O cis-pinonaldhyde C=O O polymers particle

Particle Phase reactions Gas phase reactions C=O O cis-pinonaldhyde C=O O particle polymers

Particle Phase reactions Gas phase reactions C=O O cis-pinonaldhyde C=O O polymers

MS Analysis of Filter Samples from the reaction of acid seed particles with a-pinene + O3

ESI-QTOF mass spectrum of SOA from reaction of a-pinene + O3 + acid seed aerosol (Tolocka et. al., 2004)

Particle phase pinonaldehyde dimers from a-pinene +O3 on acid particles M Na+ (ESI-QTOF Tolocka et al, 2003) Similar results were obtain by Hartmut Herrmann’s group (Atmos Envir, 2004)

Kalberer and Baltensperger et al Kalberer and Baltensperger et al. (Science, 2004) identified polymers as the main constituents of SOA formed from the photo-oxidation of 1,3,5-trimethylbezene. These account for about 50% of the aerosol mass after 30 hours of aging. Without acid seed injection

LDI-TOFMS Spectrum of SOA from Photo-oxidation of 1,3,5-Trimethylbezene This is a LDI-TOFMS spectrum of SOA resulting from photo-oxidation of 650ppbv 1,3,5-TMB. Aerosol sample was collected on steel plates using impactor 5-7.5hrs after start of the photo-oxidation. So far all the compounds identified in the literature are small and just have mass up to aprroximately 200Da. But in this spectrum, a group of peaks are shown in the mass range 400<m/z<900 and they have highly regular mass differences of m/z 14, 16 and 18. Such a regular structure is typical for polymers, suggesting that polymerization reactions are taking place in the aerosol particles.

Time Evolution of Polymer in SOA Measured by LDI-MS 2.5hrs 3.5hrs 4.5hrs 6.5hrs It’s very obvious that with increasing time, the molecular size distribution shifts to higher masses. In spectrum E MGLY shows oligomers up to the 9-mer with m/z=723. One thing we need to keep in mind is that in their experiment, no acidic seed was injected in to the chamber, which means that the organic acids and nitric acid in particle phase have sufficiently high concentrations to catalyze polymerization reactions. Theses measurements proved that polymerization in atmospheric aerosols could take place also without acidic seed particle and in a wide range of atmospheric conditions. methylglyoxal oligomers mixture of methylglyoxal, formaldehyde, 2,5-dimethylbenzaldehyde, and pyruvic acid

Where do we go from here for isoprene?? Learn what products it makes that go into the particle phase Begin to describe the chemistry Start to collect papers on isoprene and SOA